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Mobilkrane arbeiten regelmäßig in Regionen, in denen Temperaturen bis -60 °C herrschen. In sicherheitstechnisch bedeutsamen Anwendungen wird der Kranbetrieb eingestellt, und zwar nur, weil in den entsprechenden Regelwerken die niedrigste genannte Arbeitstemperatur -40 °C ist. Aber ist dies technisch zwingend? Es wird über Versuche mit Seilen und Seildrähten berichtet, die sowohl bis -95 °C als auch bei Raumtemperatur durchgeführt wurden. Sowohl das Ermüdungsverhalten der Seildrähte als auch die Bruchkraft der Seile sind bei Temperaturen von -60 °C besser als bei Raumtemperatur. Dagegen wird das Ermüdungsverhalten der Seile schlechter. Dies ist aber hauptsächlich verursacht durch das Verhalten des verwendeten Konservierungsstoffs. Im Betrieb sind die Seile zusätzlich mit Endverbindungen versehen. Diese Komponenten müssen ebenfalls solchen tiefen Temperaturen widerstehen. Untersuchungen, ob Seilendverbindungen bei Tieftemperatur geeignet sind, waren allerdings nicht Gegenstand dieses Berichts. Daher ist es ratsam, beim Betrieb bei Tieftemperatur die Intervalle der Seilinspektion zu verkürzen. Konservierungsstoffe können ihre Wirkung verlieren und zu beschleunigter Seilermüdung führen - zum Beispiel bei Auslegerverstellseilen von Mobilkranen - und das Zusammenwirken von Seilen und ihren Endverbindungen bei tiefen Temperaturen ist nicht ausreichend erforscht und dokumentiert. Insgesamt können Seile bei Temperaturen von -60 °C sicher betrieben werden, wenn sowohl die Seile als auch ihre Endverbindungen regelmäßig inspiziert werden.
This paper explores the efficacy of employing local damage models, normally applied to ductile material systems manufactured by subtractive techniques, to additively manufactured laboratory specimens. While these specimens were ductile and metallic, their additive character (i.e. porosity and surface roughness) could have had potential to activate multiple life-limiting failure paths, thus obfuscating failure prediction. Herein, two damage models are considered and compared: the micromechanical Gurson–Tvergaard–Needleman model and a Crack Band model of the strain-based, phenomenological genre. Simulations used to calibrate elastic and plastic material properties and predict damage in a novel, non-standard specimen were quasi-static, explicit. Both damage models proved capable in resolving the experimentally-observed failure path and associated loading conditions. The analyses described herein were made as part of the Third Sandia Fracture Challenge.
Transient surrogate modeling of modally reduced structures with discontinuous loads and damping
(2024)
In this work, a surrogate model for structural, transient and discontinuously excited finite element method simulations is developed. This allows to reduce the computational effort of repeated calculations of identical models under different load cases. The architecture of the surrogate combines fully connected neural network layers with long short-term memory layers. For the reproduction of different damping ratios, a categorical variable is added to the continuous input data. Based on a recursive flow of the predicted data back to the input layer, long-term dependencies do not vanish due to short-input sequences. The system dimension is reduced by applying the model-order reduction technique for modal decomposition. The high accuracy of the surrogate and the reduction of computational costs are shown on an academic example of a cantilever beam and a real-world example of a robot. The advantages of our approach are illustrated in comparison with state-of-the-art surrogates for transient finite element analysis. By using the surrogate proposed in this study, oscillations due to discontinuous excitation of mechanical structures can be reproduced. For this purpose, only short-input sequences are necessary since the excitation of the oscillations does not have to be part of the input sequence during the whole duration of the oscillations. Due to the categorical variable for the damping ratio, the surrogate can account for the influence of different damping in parameter studies.
Fiber-reinforced plastic (FRP) tubes are used in many different industries, such as electrical engineering and pipeline construction. The tubes are frequently subjected to bending loads, depending on the application. In order that the dimensioning of the tubes can be ensured, analytical bending models are used to calculate the resulting stresses, strains and displacements in the individual layers of the laminate. This enables the making of a statement about the failure of the fiber-reinforced tube by choosing an appropriate failure criterion. For the use of these bending models, it is necessary to understand the respective underlying theory. The theory provides the basis for the mathematical description of the mechanical properties for a single-layered tube and using the relationships between the stresses and strains that occur in the Cylindrical coordinate system for this calculation step. For this reason, a redefinition of the compliance matrix from the transformation about the winding angle to the Cylindrical coordinate system and a modification of the stress and strain vectors is necessary, because the defined Cartesian coordinate system of the model cannot be used for wounded FRP tubes. The transformation causes an exchange of entries in the compliance matrix, which remain in the correct relationship between the particular stress and strains. This step is not specified and may lead to incorrect results due to the incorrect entry of compliances. The present publication refers to sketch on this issue and represent a simplification of the changeover to the level required by the bending models notation of vectors in the form of a permutation. In addition, a new name for the pre-acquisition of the redefined compliances is given to prevent confusion when entering the material law of a bending model. Finally, the permuted and redefined compliances are proved in an example to determine their accuracy.
Bisher wurden TPM und Lean Production meist differenziert voneinander betrachtet. Der TPM-Gedanke ist jedoch die konsequente Fortführung des Lean Thinking. Ein effektives Anlagenmanagement ist die Voraussetzung für das Erzeugen eines Produktionsflusses. In der Vergangenheit wurde TPM häufig ohne die Basis eines Produktionssystems eingeführt. Der zweite Schritt erfolgte vor dem ersten. Logistische Themen und die Optimierung von Arbeitsplätzen mitarbeiterintensiver Bereiche wurden ebenfalls nur mit geringer Tiefe behandelt. Die OEE (Overall Equipment Effectiveness) allein ist hierbei kein ausreichender Indikator für ein schlankes Produktionssystem, da eine Rüstzeitoptimierung mit der Reduzierung der Losgröße einen Zielkonflikt hervorrufen kann. Ein Ansatz, bei dem die EPEI-Kennzahl (Every Part Every Intervall) und die OEE gemeinsam betrachtet werden, stellt eine Lösung dar. Durch die verstärkte Fokussierung auf Ganzheitliche Produktionssysteme rückt TPM als ein wichtiger Baustein, oder bei einer entsprechenden Weiterentwicklung zum System, als aufbauender Ansatz in den Blickpunkt der Unternehmen.
The Sandia Fracture Challenges provide a forum for the mechanics community to assess its ability to predict ductile fracture through a blind, round-robin format where mechanicians are challenged to predict the deformation and failure of an arbitrary geometry given experimental calibration data. The Third Challenge (SFC3) required participants to predict fracture in an additively manufactured (AM) 316L stainless steel bar containing through holes and internal cavities that could not have been conventionally machined. The volunteer participants were provided extensive data including tension and notched tensions tests of 316L specimens built on the same build-plate as the Challenge geometry, micro-CT scans of the Challenge specimens and geometric measurements of the feature based on the scans, electron backscatter diffraction (EBSD) information on grain texture, and post-test fractography of the calibration specimens. Surprisingly, the global behavior of the SFC3 geometry specimens had modest variability despite being made of AM metal, with all of the SFC3 geometry specimens failing under the same failure mode. This is attributed to the large stress concentrations from the holes overwhelming the stochastic local influence of the AM voids and surface roughness. The teams were asked to predict a number of quantities of interest in the response based on global and local measures that were compared to experimental data, based partly on Digital Image Correlation (DIC) measurements of surface displacements and strains, including predictions of variability in the resulting fracture response, as the basis for assessment of the predictive capabilities of the modeling and simulation strategies. Twenty-one teams submitted predictions obtained from a variety of methods: the finite element method (FEM) or the mesh-free, peridynamic method; solvers with explicit time integration, implicit time integration, or quasi-statics; fracture methods including element deletion, peridynamics with bond damage, XFEM, damage (stiffness degradation), and adaptive remeshing. These predictions utilized many different material models: plasticity models including J2 plasticity or Hill yield with isotropic hardening, mixed Swift-Voce hardening, kinematic hardening, or custom hardening curves; fracture criteria including GTN model, Hosford-Coulomb, triaxiality-dependent strain, critical fracture energy, damage-based model, critical void volume fraction, and Johnson-Cook model; and damage evolution models including damage accumulation and evolution, crack band model, fracture energy, displacement value threshold, incremental stress triaxiality, Cocks-Ashby void growth, and void nucleation, growth, and coalescence. Teams used various combinations of calibration data from tensile specimens, the notched tensile specimens, and literature data. A detailed comparison of results based of these different methods is presented in this paper to suggest a set of best practices for modeling ductile fracture in situations like the SFC3 AM-material problem. All blind predictions identified the nominal crack path and initiation location correctly. The SFC3 participants generally fared better in their global predictions of deformation and failure than the participants in the previous Challenges, suggesting the relative maturity of the models used and adoption of best practices from previous Challenges. This paper provides detailed analyses of the results, including discussion of the utility of the provided data, challenges of the experimental-numerical comparison, defects in the AM material, and human factors.
Ductile failure of structural metals is relevant to a wide range of engineering scenarios. Computational methods are employed to anticipate the critical conditions of failure, yet they sometimes provide inaccurate and misleading predictions. Challenge scenarios, such as the one presented in the current work, provide an opportunity to assess the blind, quantitative predictive ability of simulation methods against a previously unseen failure problem. Rather than evaluate the predictions of a single simulation approach, the Sandia Fracture Challenge relies on numerous volunteer teams with expertise in computational mechanics to apply a broad range of computational methods, numerical algorithms, and constitutive models to the challenge. This exercise is intended to evaluate the state of health of technologies available for failure prediction. In the first Sandia Fracture Challenge, a wide range of issues were raised in ductile failure modeling, including a lack of consistency in failure models, the importance of shear calibration data, and difficulties in quantifying the uncertainty of prediction [see Boyce et al. (Int J Fract 186:5-68, 2014) for details of these observations]. This second Sandia Fracture Challenge investigated the ductile rupture of a Ti-6Al-4V sheet under both quasi-static and modest-rate dynamic loading (failure in 0.1 s). Like the previous challenge, the sheet had an unusual arrangement of notches and holes that added geometric complexity and fostered a competition between tensile- and shear-dominated failure modes. The teams were asked to predict the fracture path and quantitative far-field failure metrics such as the peak force and displacement to cause crack initiation. Fourteen teams contributed blind predictions, and the experimental outcomes were quantified in three independent test labs. Additional shortcomings were revealed in this second challenge such as inconsistency in the application of appropriate boundary conditions, need for a thermomechanical treatment of the heat generation in the dynamic loading condition, and further difficulties in model calibration based on limited real-world engineering data. As with the prior challenge, this work not only documents the 'state-of-the-art' in computational failure prediction of ductile tearing scenarios, but also provides a detailed dataset for non-blind assessment of alternative methods.
In tension-tension tests the amplitude stress as well as the mean stress can be adjusted to any desired level. For a common evaluation of all tension-tension tests amplitude and mean stresses should be substituted by an equivalent amplitude stress. For determination of these e quivalent stress the so called mean stress influence hast to be known. In the following, suitable models will be presented which allow a common evaluation of all tension-tension tests and also a general description of rope wire fatigue behavior.
In the context of the “InnMag” project, partners from industry and science are co-operating to investigate the issues involved in adapting established production processes to the material Mg. The project's aim is to further the deployment of Mg interior parts in civil aircraft. The project covers every production step, from alloy selection, Mg ingot melting, alloying, direct chill casting, extruding, machining, surface treatment and component assembly. This paper discusses the project's targets and the results arrived at so far, particularly in the areas of direct chill casting and extrusion.
Mg and Mg alloys are becoming more and more of interest for several applications. In the case of biomaterial applications, a special interest exists due to the fact that a predictable degradation should be given. Various investigations were made to characterize and predict the corrosion behavior in vitro and in vivo. Mostly, the simple oxidation of Mg to Mg2+ ions connected with adequate hydrogen development is assumed, and the negative difference effect (NDE) is attributed to various mechanisms and electrochemical results. The aim of this paper is to compare the different views on the corrosion pathway of Mg or Mg alloys and to present a neglected pathway based on thermodynamic data as a guideline for possible reactions combined with experimental observations of a delay of visible hydrogen evolution during cyclic voltammetry. Various reaction pathways are considered and discussed to explain these results, like the stability of the Mg+ intermediate state, the stability of MgH2 and the role of hydrogen overpotential. Finally, the impact of MgH2 formation is shown as an appropriate base for the prediction of the degradation behavior and calculation of the corrosion rate of Mg and Mg alloys.
Purpose: A route to manufacture porous carbon fiber reinforced plastic (CFRP) for study purposes is described. Design/methodology/approach: The porous CFRP is characterized using standard techniques such as matrix digestion as well as the more sophisticated method of high resolution Microfocus X-Ray Tomography (μCT). A comparison of the results of those methods is presented. The mass gains of specimens with a wide range of porosity have been measured both in constant humidity and in alternating environments. Findings: It could be shown that severe temperature changes can temporarily increase the moisture content of porous CFRP. However, after the return to a constant environment, the moisture content returns back to saturation levels. Furthermore, it could be shown by X-Ray Tomography that even under severe climatic conditions no permanent liquid water condensates inside the pores. Research limitations/implications: Using Microfocus Computed Tomography it could be shown that even after nearly a year under hot-wet conditions and more than 150 severe temperature cycles there is no liquid water detectable inside the pores. Originality/value: In this paper the effects of severe temperature changes and high humidity on porous CFRP.
The focus of this paper is the characterization of the influence of the temperature rates on the TMF lives. Therefore static and the dynamic calibrations of the temperature measurement devices were compared by a custom-built calibration specimen, which included five internal mantle thermocouples. Additionally the temperatures were measured on the specimens' surface. The experimental setups used were compared by executing TMF pre-test with the identical single-crystalline specimen. Subsequently TMF tests on coated single-crystalline Nickel-based superalloy PWA 1484 were carried out with temperature rates of 10K/s and 20 K/s. Finally the deviations of the determined TMF lives were evaluated.
Test Setup for Investigating the Impact Behavior of Biaxially Prestressed Composite Laminates
(2024)
Instrumented impact testing and compression-after-impact testing are important to adequately qualify material behavior and safely design composite structures. However, the stresses to which fiber-reinforced plastic components are typically subjected in practice are not considered in the impact test methods recommended in guidelines or standards. In this paper, a test setup for investigating the impact behavior of composite specimens under plane uniaxial and biaxial preloading is presented. For this purpose, a special test setup consisting of a biaxial testing machine and a specially designed drop-weight tower was developed. The design decisions were derived from existing guidelines and standards with the aim of inducing barely visible impact damage in laminated carbon fiber-reinforced plastic specimens. Several measurement systems have been integrated into the setup to allow comprehensive observation of the impact event and specimen behavior. A feasibility test was performed with biaxially prestressed carbon fiber-reinforced plastic specimens in comparison with unstressed reference tests. The compressive-tensile prestressing resulted in lower maximum contact forces, higher maximum deflections, higher residual deflections and a different damage pattern, which was investigated by light microscopic analysis. Finally, the functionality of the experimental setup is discussed, and the results seem to indicate that the test setup and parameters were properly chosen to investigate the effect of prestresses on the impacts behavior of composite structures, in particular for barely visible subsequent damages.
Due to the growing number of applications for Additive Manufacturing (AM), an increasing need for enhanced quality control methods exists. Here optical measurement techniques are often used for in-situ monitoring in AM. There is a great potential to standardize and improve applications of optical measurement devices in accordance to the increasing requirements of measuring tasks. Beside the optical material qualifications, especially process-oriented changes in optical effects are of great relevance for in-situ evaluations. The optical modifications may be attributed to aggregate specific phase transitions coming along with variable emitted wavelengths. A measuring setup with two integrations spheres and a heated process chamber have been developed to analyze the optical interactions of laser radiation and visual illumination with the powder. The process oriented analysis for selective laser sintering lead to improved operating conditions in the field of in-situ measurements in combination with an accurate evaluation of the absorption ratio of the examined powder.
Die Regensburg Robotics Research Unit entwickelt Regelungsarchitekturen für Telerobotiksysteme für den industriellen Einsatz. Der Beitrag beschreibt das lokale und globale Regelungsmodell hinsichtlich Stabilität und Transparenz auf der Basis der von Lawrence und Yokokohji vorgestellten Regelungsarchitektur und zeigt Simulationsergebnisse auf. Die Modellbildung des geregelten Manipulators, die Kopplung des Operators und des Teleoperators und sowie die Übertragungsfunktion werden dargestellt. Die Simulation des vorgestellten Algorithmus in Matlab/Simulink wird durchgeführt. Innerhalb der Simulationsumgebung ist als Regelstrecke unter der Annahme einer idealen, lokalen Regelung eine im Raum bewegliche Punktmasse modelliert. Die vorgestellte Regelungsarchitektur liefert innerhalb der durchgeführten Simulation vor allem im niederfrequenten Bereich sehr gute Ergebnisse. Die nächsten Schritte sind die experimentelle Evaluierung der lokalen Architektur und der globalen Vierkanalarchitektur an den Robotern.
Methanol, and more recently ethanol, have been deeply employed as adsorbate phase (refrigerant) in adsorption chiller and heat pump applications (e.g. refrigerator adsorption ice maker). The use of anhydrous alcohols however can cause several problems related to the corrosiveness of such molecules towards light alloys (from titanium to aluminium). The problem was already highlighted in bio-fuel technology where bio-ethanol was considered as a promise alternative to fossil hydrocarbons. Water content was observed as one of the main factors influencing corrosion rate. In the present works several accelerated corrosion tests on 6061 Aluminium alloy have been carried out in autoclave in a temperature range from 110 to 135 degrees C with different ethanol to aluminium mass ratio. Highly exothermic reactions related to aluminium oxidation, coupled to hydrogen evolution, have been recorded. The main drawback of hydrogen evolution is the formation of a stagnant layer over the heat exchangers surface, which can limit the ethanol vapour diffusion, thus reducing adsorption condensation rate. (C) 2016 Elsevier Ltd. All rights reserved.
Purpose:
A review regarding the acting mechanisms of structural dynamic material damping in fabric reinforced composites is presented. Design/methodology/approach:
Mechanical acting principles identified by different investigations are considered. Aspects of the determination and calculation of structural mechanical material properties of fabric reinforced composites are described. Approaches intending the description and classification of ondulations in fabrics reinforced single layers are demonstrated.
Findings:
The mesomechanic geometry of fabrics is not considered sufficiently by relatively simple homogenization approaches. Yet, it significantly affects its structural dynamic material properties, especially the dynamic ones.
Research limitations/implications:
In each case the different damping mechanisms act coupled and occur at the same time. Therefore a separation procedure is required in any case. Practical implications: Against the background of the comparison and remarks of the presented papers a reasonable further procedure is recommended. Thereby, FE-calculations with a parametrical variation of the mesomechanic geometry in order to identify kinematic correlations due to geometric constraints are suggested.
Originality/value:
The idea of the representation of the geometric conditions in terms of a degree of ondulation is described. Such a non-dimensional specific value representing the intensity of the ondulation would enable the comparability of the results of different kinds of investigations.
Abrasive wear limits the lifetime of many machine components. Most empirical models relate the abrasive wear resistance to material hardness. In reality, however, other material properties are also influencing as scratch abrasion damage follows from a highly complex stress trajectory upon scratching. Numerical (finite element) simulation of scratch abrasion requires the use of a material damage model, which translates this stress trajectory into material degradation and removal. Most damage models include the first two stress invariants. However, fully incorporating the complex stress trajectories that occur during scratch abrasion may require damage models with dependence of the third deviatoric parameter (Lode angle). This paper serves as an a-priori study to evaluate the stress states that may occur during scratch abrasion. Three mechanisms (ploughing, wedging, cutting) are considered. Hereto, the results of an extensive parametric study using elastic-plastic finite element simulations of a scratch indentation process are discussed. Complex, non-proportional variations in stress state values are observed to occur during scratch abrasion. Distinct stress state trajectories are identified for the three abovementioned mechanisms. These variations are critically discussed to motivate a selection of suitable damage models for rigorous finite element analysis of the wear processes associated with scratch abrasion.
Der Beitrag beschreibt den Systemaufbau für die Risikobeurteilung zur Realisierung einer sicheren Mensch-Maschine-Kollaboration und stellt die vorgeschriebene Risikobeurteilung gemäß DIN EN ISO 10218-1:2012-01 in folgende Schritten vor: Beurteilung der Erfahrenswerte und des Nutzerverhaltens, Festlegung der Grenzen des Roboters, Identifikation der Gefährdungen und Risikoeinschätzung in den dimensionen Ausmaß, Exposition, Eintrittswahrscheinlichkeit und Vermeidungsmöglichkeit. Die Umsetzung in eine Steuerung, die Steuerungsarchitektur und die eingesetzten Komponenten zur Realisierung einer sicheren Abstandsüberwachung werden beschrieben und in Blockschaltbildern grafisch dargestellt. Die Validität der Sicherheitsfunktion wird diskutiert.
Filament wound composite structures are widely used in the field of pressure vessels, tubes, pipelines or rocket cases. The mechanical behavior of these structures is typically different from those of flat laminated structures due to an alternating lay-up sequence, winding tension and manufacturing induced imperfections. However, design and analysis issues require the same engineering data as used for laminated structures in general. It has therefore become necessary to establish an accompanying quality assurance procedure following the production process to identify the material properties of the manufactured tubes especially for the single layer. Consequently, there are three different approaches of determining the elastic moduli and tensile strengths of a filament wound laminate. Either specimens are resected from a curved tube, from a tube with plane areas or standardized flat specimens are manufactured under deviating production conditions. All approaches entail disadvantages, whether in terms of manufacturing or testing parameters including geometry, lay-up sequence, porosity, fiber tension and load direction. This study presents the discrepancies in the determination of mechanical properties of a filament wound glass-fiber-reinforced polymer tube on curved or cylindrical specimens and flat specimens produced to meet the specifications of international standards. In order to obtain material properties not only in longitudinal but also in transverse direction of the tubes, the so-called split-disk tensile test modeled after ASTM Standard D 2290, is used with tube segments.The procedures of specimen production and preparation are described in detail. Material properties such as the fiber volume and void content of the composite specimens are conducted in order to consider quality and production differences. Finally tensile tests are performed and the results are compared and discussed.
By simultaneous laser beam melting (SLBM), parts consisting of different polymer powders can be additively manufactured within one building process. Besides the advantages of conventional LBM, e.g., not needing additional tools and being able to realize parts with almost any geometry, different product requirements can be achieved within a single part. Product requirements may be different chemical resistances or haptic material properties. Therefore, SLBM enlarges the application field for additive manufacturing in general. In the process, two different materials are deposited on the building platform and preheated a few degrees below the melting temperature of the lower melting polymer by infrared emitters. Afterward, a CO2 laser (λ = 10.6 μm) provides the energy for the temperature difference between the preheating temperatures of both materials. Finally, a digital light processing chip is used to achieve simultaneous and flexible energy deposition for melting both preheated polymers. By illuminating the chip with a laser, parts of the beam can be flexibly guided onto the powder bed or into a beam trap. As laser, a single mode thulium laser (λ = 1.94 μm) is used. After melting the layer, a new layer is deposited and the process starts anew. In this paper, polypropylene and polyamide 12 are used as materials. After analyzing the material and melting behavior during the process by a high-resolution thermal imaging system, the parts are qualified regarding their material compatibility at the boundary zone and porosity by cross sections.
Thermomechanical shape memory materials have certain disadvantages when it comes to 3D volumetric reproduction intended for rapid prototyping or robotic prehension. The need to constantly supply energy to counteract elastic retraction forces in order to maintain the required geometry, together with the inability to achieve conformal stability at elevated temperatures, limits the application of thermal shape memory polymers. Form removal also presents problems as most viscoelastic materials do not ensure demolding stability. This work demonstrates how magnetoactive boron−organo−silicon oxide polymers under the influence of an applied magnetic field can be used to achieve energy free sustainable volumetric shape memory effects over extended periods. The rheopectic properties of boron−organo−silicon oxide materials sustain form removal without mold distortion.
Die 3D-Daten, die bei der Fertigungsplanung in CAD/CAM-Systemen vorliegen, bilden häufig auch die Spannsituation des Werkstücks ab. Mit einer vom LFW der OTH Regensburg entwickelten Software lassen sich die Konturen direkt auf den Rüstplatz projizieren. Im Rahmen des durch das Bayerische Staatsministerium für Bildung und Kultus, Wissenschaft und Kunst geförderte F&E-Projekt "AutoRüst" entwickelt das LFW Bausteine zum automatisierten Generieren von Rüstinformationen. Im Wesentlichen geht es dabei um zwei Schwerpunkte: erstens das datenbankgestützte Verwalten von Spannsituationen inklusive der Unterstützung und Überprüfung beim Aufbau sowie zweitens die bedarfsgerechte Visualisierung des Programmablaufs für die Einfahrprozedur an der Werkzeugmaschine. Bei beiden Themenkomplexen werden bereits vorhandene Daten (3D-Spannsituation, NC-Programm mit Maschinenraumsimulation) genutzt, um konfigurierbare Rüstdokumente zum Spannen und Einfahren zu erzeugen. Im Idealfall muss der NC-Programmierer also nur wenige bis gar keine zusätzlichen Eingaben tätigen. Neben der reinen Zeitersparnis wird so auch eine deutlich gesteigerte Prozesssicherheit beim Übertragen der virtuellen Welt in die reale Fertigungswelt erreicht. Das vom LFW entwickelte Modul zur Visualisierung der Spannsituation kann flexibel in den Fertigungsbetrieben integriert werden. Gerüstet werden kann sowohl in der Maschine, auf einer zweiten Palette als auch auf einem externen Rüstplatz. Einzige Randbedingung ist, dass der Laserprojektor auf den Tisch projizieren kann, idealerweise senkrecht von oben. Die Software analysiert in einem ersten Schritt die vorhandene 3D-Baugruppe und erzeugt anhand der Lage der Bauteile eine Montagereihenfolge, die natürlich angepasst werden kann. Ebenso können Einzelteile gruppiert werden, sodass diese bei der späteren Projektion auch als Gruppe projiziert werden. Unwichtige Baugruppenteile wie beispielsweise die Stützen der Spannpratzen oder die Muttern mit den Unterlegscheiben können vom weiteren Prozess ausgeschlossen werden. Auf der so geschaffenen Grundlage erzeugt die Software Projektionslinien auf dem zu positionierenden Bauteil mit einem einstellbaren Abstand (hier: 1 mm) zur Bauteilkante. Als Ergebnis wird eine Ausgabedatei im dxf-Format erstellt, die vom Laserprojektor verarbeitet werden kann. Die in der dxf-Datei auf Layern gruppierten Projektionslinien können dann ferngesteuert in der zuvor definierten Reihenfolge durchgeklickt werden, um die Spannelemente zu positionieren. Die Vorteile des Visualisierungsmoduls im Überblick: (1) Senken der Rüstzeit; (2) Erhöhen der Prozesssicherheit beim Rüsten (Positioniergenauigkeit der Spannelemente < 1 mm) und damit Kollisionsvermeidung; (3) Nutzen bereits vorhandener 3D-Informationen entlang der Prozesskette CAD/CAM-Fertigung; (4) Konturerzeugung direkt im CAM-System OPUS oder über unabhängige Software.
Review of elasto-static models for three-dimensional analysis of thick-walled anisotropic tubes
(2023)
Most shell or beam models of anisotropic tubes under bending have no validity for thick-walled structures. As a result, the need to develop three-dimensional formulations which allow a change in the stress, strain and displacement distributions across the radial component arises. Basic formulations on three-dimensional anisotropic elasticity were made either stressor displacement-based by Lekhnitskii or Stroh on plates. Lekhnitskii also was the first to expand these analytical formulations to tubes under various loading conditions. This paper presents a review of the stress and strain analysis of tube models using three-dimensional anisotropic elasticity. The focus lies on layered structures, like fiber-reinforced plastics, under various bending loads, although the basic formulations and models regarding axisymmetric loads are briefly discussed. One section is also dedicated to the determination of an equivalent bending stiffness of tubes.
The development of reconfigurable planar four-bar linkages by applying the tensegrity principle is considered. Conventional quadrilateral linkages enable two operation modes differing in the kinematic behavior. However, a change between these states is not possible due to the geometric constraints. To enable a reconfiguration between the different modes one-sided limited nonholonomic constraints are introduced in this work. This issue is realized by applying ropes that cannot resist compression. However, to guarantee an appropriate load case in operation a prestress within the mechanism is required. Hence, the linkage is extended to a tensegrity-based mechanism. The structural dynamics are derived using the LAGRANGE formalism and the structural behavior is evaluated using numerical simulations. Furthermore, a prototype of an exemplary tensegrity-based mechanism is manufactured and experiments regarding the mechanical properties, in particular the reconfiguration, are performed. The results suggest the potential benefit of applying the tensegrity principle within conventional planar four-bar linkages.
In this paper, first results regarding the realization of multi-material parts by Simultaneous Laser Beam Melting (SLBM) of polymers are presented. This new approach allows the layerwise generation of parts consisting of different polymer materials within one building process. Besides the typical advantages of additive manufacturing technologies, such parts can fulfill different product requirements concomitant and therefore could enlarge the overall field of application. The powder materials used for this paper are polyethylene (PE) and a polyamide based thermoplastic elastomer (TPE). After depositing the powder materials next to each other, infrared-emitters heat the lower melting polymer and a CO2 laser provides the preheating temperature of the higher melting polymer. In the last step, a thulium fibre laser melts the two preheated powders simultaneously. The realized specimens are characterized by cross sections and their tensile strengths are determined. Additionally, the new approach of the simultaneous energy irradiation is investigated using a Finite Element Analysis in order to gain a more profound process understanding. In that sense, the influence of the size of the exposure area on the reachable maximum temperatures inside that area was analyzed by the simulation and compared to experimental studies.
In this paper, first results regarding the realization of multi-material parts by Simultaneous Laser Beam Melting (SLBM) of polymers are presented. This new approach allows the layerwise generation of parts consisting of different polymer materials within one building process. Besides the typical advantages of additive manufacturing technologies, such parts can fulfill different product requirements concomitant and therefore could enlarge the overall field of application. The powder materials used for this paper are polyethylene (PE) and a polyamide based thermoplastic elastomer (TPE). After depositing the powder materials next to each other, infrared-emitters heat the lower melting polymer and a CO2 laser provides the preheating temperature of the higher melting polymer. In the last step, a thulium fibre laser melts the two preheated powders simultaneously.The realized specimens are characterized by cross sections and their tensile strengths are determined. Additionally, the new approach of the simultaneous energy irradiation is investigated using a Finite Element Analysis in order to gain a more profound process understanding. In that sense, the influence of the size of the
exposure area on the reachable maximum temperatures inside that area was analyzed by the simulation and compared to experimental studies.
Im Betrieb von Förderbändern auftretende Phänomene sind das Bandwandern in Achsrichtung der Walzen und die Bandverformung in der Bandebene [1, S. 142]. Das Bandwandern ist bisher detailliert untersucht [2–4], während die Bandverformung Gegenstand weniger Veröffentlichungen ist. Deshalb wird in diesem Artikel eine Methode zur Berechnung der sich im dynamischen Betrieb einstellenden Verformung eines elastischen Förderbandes vorgestellt. Dazu wird ein Mehrkörpersimulations-Modell basierend auf der Lumped-Mass-Modellierung verwendet. Als Untersuchungsbeispiel dient ein Zwei-Walzensystem mit flexiblen und zylindrischen Walzen, sowie ein flexibles Förderband. Es zeigt sich, dass mit der Lumped-Mass-Modellierung eine dynamische Bandverformung, die von der gewählten Diskretisierung abhängt, berechnet werden kann. Aufgrund dieser Abhängigkeit ist es notwendig eine Konvergenzanalyse durchzuführen. Zusätzlich ist darauf zu achten, dass die künstliche Anregung aufgrund der Lumped-Mass-Modellierung nicht mit einer Eigenfrequenz des Modells zusammenfällt.
A pyrometer, integrated into a 3D‐scanner, offers the possibility to measure the weld seam temperature at quasi‐simultaneous laser transmission welding. Experimental studies have shown that gaps located in the joining zone can be identified by a temperature rise even at a high scanning velocity. This enables the implementation of algorithms for observation and control strategies.
An over-the-counter methodology to predict fracture initiation and propagation in the challenge specimen of the Second Sandia Fracture Challenge is detailed herein. This pragmatic approach mimics that of an engineer subjected to real-world time constraints and unquantified uncertainty. First, during the blind prediction phase of the challenge, flow and failure locus curves were calibrated for Ti–6Al–4V with provided tensile and shear test data for slow (0.0254 mm/s) and fast (25.4 mm/s) loading rates. Thereafter, these models were applied to a 3D finite-element mesh of the non-standardized challenge geometry with nominal dimensions to predict, among other items, crack path and specimen response. After the blind predictions were submitted to Sandia National Labs, they were improved upon by addressing anisotropic yielding, damage initiation under shear dominance, and boundary condition selection.
In this report, the dry delivery of polyamide 12 powders by vibrating capillary steel nozzles is investigated and discussed regarding its potential for powder layer preparation in Laser Beam Melting. Therefore, a setup including a steel nozzle assembled on a piezoelectric actuator is presented, which enables the precise control over very small powder quantities by vibration excitation. An analysis reveals that the mass flow through the nozzle can be adjusted by the vibration modes in a certain range depending on the nozzle's specifications, whereas the vibration modes themselves show a complicated behaviour. Using a positioning system in combination with the vibrating nozzle, single-layer patterns consisting of polyamide 12 are produced and characterized regarding surface homogeneity and selectivity using a laser stripe sensor.
Abstract — In this report, the dry delivery of polyamide 12 (PA 12) powder for the preparation of powder layers in laser beam melting (LBM) is investigated. Therefore, an experimental setup was built which consists of a glass nozzle assembled on a piezo-electric actuator. By applying a sinusoidal voltage signal to the actuator, the nozzle is set into vibration mode which enhances the powder delivery through the nozzle. By using this effect, powder mass flow is controlled and a valve-like start and stop function is realized. In order to identify suitable process parameters, a broad range of vibration modes were investigated using two nozzles made from glass with different orifice diameters. Therefore, the vibration frequency and the voltage signal of the actuator were varied and the resulting mass flow was detected by a balance. It was found that both the frequency and the voltage signal affect the mass flow and its stability but with different impact. Moreover, powder lines were deposited with different velocities in order to characterize the setup regarding applicability for highly selective powder deposition for LBM.
This study investigates the vibration reduction of tall wind-excited buildings using a tuned mass damper (TMD) with an inerter (TMDI). The performance of the TMDI is computed as a function of the floor to which the inerter is grounded as this parameter strongly influences the vibration reduction of the building and for the case when the inerter is grounded to the earth whereby the absolute acceleration of the corresponding inerter terminal is zero. Simulations are made for broadband and harmonic excitations of the first three bending modes, and the conventional TMD is used as a benchmark. It is found that the inerter performs best when grounded to the earth because, then, the inerter force is in proportion to the absolute acceleration of only the pendulum mass, but not to the relative acceleration of the two inerter terminals, which is demonstrated by the mass matrix. However, if the inerter is grounded to a floor below the pendulum mass, the TMDI only outperforms the TMD if the inerter is grounded to a floor within approximately the first third of the building’s height. For the most realistic case, where the inerter is grounded to a floor in the vicinity of the pendulum mass, the TMDI performs far worse than the classical TMD.
In recent years, the Tuned Mass Damper with inerter (TMDI) has received significant attention. The inerter is defined to exert a force that is in proportion to the relative acceleration of the two inerter terminals. Here, two TMDI topologies are investigated. The conventional topology is given by the inerter being in parallel to the spring and viscous damper of the TMDI. The other topology is the serial arrangement of spring, inerter and viscous damper being in parallel to the stiffness of the mass spring oscillator of the TMDI. While the first topology intends to increase the inertial force of the TMDI, the second topology aims at producing an additional degree of freedom. The considered TMDI concepts are simulated for harmonic and random excitations, with parameters set according to those described in the literature and with numerically optimized parameters which minimize the primary structure displacement response. The classical TMD is used as a benchmark. The findings are twofold. The conventional TMDI with typical inertance ratio of 1% and the very small value of 0.02% performs significantly worse than the classical TMD with the same mass ratio. In contrast, the TMDI with an additional degree of freedom can improve the mitigation of the primary structure if the inertance ratio is set very small and if the TMDI parameters are numerically optimized.
Purpose:
A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by numerical investigations.
Design/methodology/approach:
Due to the definition of plain representative sequences of balanced plain-weave and twill-weave 2/2 fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation.
Findings:
The mesomechanic kinematic can be observed in the FE analyses for both kinds of fabric constructions.
Research limitations/implications:
The FE analyses consider elasticity and contraction due to Poisson effects, respectively, of the model under selected longitudinal strains. Practical implications: The results are evaluated at relevant positions on the centre-line of the ondulated warp-yarn of the plain representative model. A direct and linear coupling in case of the transversal kinematic behaviour, and thereby a corresponding definite reduction of the evaluated longitudinal strains in terms of the difference of the applied and determined longitudinal strains is identified.
Originality/value:
Both characteristic purely kinematic reactions due to geometric constraints directly depend on the introduced degree of ondulation. This non-dimensional parameter relates amplitude and length of one complete ondulation, and thus represents the intensity of the ondulation of the respective fabric construction.
A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by analytical and numerical investigations. Due to the definition of plain representative sequences of balanced plain-weave fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation. The mesomechanic kinematic can be observed in both the analytic model and the FE-analyses. The analytic model yields hyperbolic correlations due to the strongly simplifying presumptions that neglect elasticity. In contrast the FE-analyses yield linear correlations in much smaller amounts due to the consideration of elastic parts, yet distinctly.
Quality and reliability are of the utmost importance for manufacturing in the optical and medical industries. Absorber-free laser transmission welding enables the precise joining of identical polymers without additives or adhesives and is well-suited to meet the demands of the aforementioned industries. To attain sufficient absorption of laser energy without absorbent additives, thulium fiber lasers, which emit in the polymers’ intrinsic absorption spectrum, are used. Focusing the laser beam with a high numerical aperture provides significant intensity gradients inside the workpiece and enables selective fusing of the internal joining zone without affecting the surface of the device. Because seam size and position are crucial, the high-quality requirements demand internal weld seam monitoring. In this work, we propose a novel method to determine weld seam location and size using optical coherence tomography. Changes in optical material properties because of melting and re-solidification during welding allow for weld seam differentiation from the injection-molded base material. Automatic processing of the optical coherence tomography data enables the identification and measurement of the weld seam geometry. The results from our technique are consistent with microscopic images of microtome sections and demonstrate that weld seam localization in polyamide 6 is possible with an accuracy better than a tenth of a millimeter.
This study increases the basic understanding of optical material properties of polymer powders used in selective laser sintering (SLS). Therefore, different polymer powder materials were analyzed regarding their optical material properties with an integration spheres measurement setup. By the measurements a direct connection between the absorption behavior of the solid material and the overall optical material characteristics of the same material in powdery form could be shown. The results were used to develop an advanced explanation model for the optical material properties of powders. At present, existing explanation models only consider the occurring of multiple reflections in the gaps between the particles to explain the overall optical material properties of powder materials. Thus, by also considering the absorption behavior of the single particles, the basic understanding of the beam-matter interaction and their effect on the optical material properties of powder materials can be expanded.
In-plant milk-run systems are transportation systems, where materials are delivered from a central storage area to several points of use on defined routes and in short intervals. Milk-run systems generally enable frequent deliveries in smaller lot sizes with short lead times and low inventory at the points of use. In real milk-run systems, the number of deliveries per interval varies due to, e.g., variations in the production program. To enable efficient and stable milk-run system operations, these systems therefore must be able to cope with peaks in the number of deliveries. We develop different strategies for handling these delivery peaks and evaluate them with respect to delivery cost, lead time and service level using real material consumption data from two large companies from the automotive industry.
Production of optical and medical devices makes high demands on cleanliness, precision, visual appearance and reliability. Advantages of laser transmission welding – contactless input of energy, high precision, no adhesives and no particle formation – can be fully exploited for this use. For absorber-free welding, lasers emitting in the polymers’ intrinsic absorption spectrum between 1.6 μm and 2 μm are used. Focusing the laser beam with high NA provides large intensity gradients inside the specimen and enables selective fusing of the joining zone without affecting the surface. Since a molten upper surface leads to visible and palpable irregularities and causes warpage, the verticalexpansion of the weld seam is crucial. To meet the high quality and reliability required in the medical and optical industry, online monitoring of the seam is necessary. The aim of this work is the localization and evaluation of the weld seam using pyrometry. First, the emitted thermal radiation is computed, enabling signal analysis regarding origin and spectrum. Thus, assessment of measurement spectrum and forecast of the signal in dependence on seam shape and position is possible. Finally, welding tests with Topas 8007-04 are performed at 200 mm/s feed rate and monitored with 100 kHz. The comparison of tracked data with thin-cuts demonstrates that weld seam localization by pyrometry is possible, enabling online assessment of the process.
Hot pressing of pure Ti and cast iron under vacuum formed a ~15 μm wide TiC-layer through the thermoreactive diffusion process. Nanoindentation testing of the TiC-layer revealed average hardness and elastic
modulus values of ~35 GPa and ~400 GPa, respectively. High-resolution indentation mapping indicated hardness change across the boundary with peak values observed within the TiC-layer. Solid state high temperature diffusion holds significant potential for developing uniform hard coatings on pure Ti/Ti-alloys.
It is well known that mechanical surface treatments, such as deep rolling, shot peening and laser shock peening, can significantly improve the fatigue behavior of highly-stressed metallic components. Deep rolling (DR) is particularly attractive since it is possible to generate, near the surface, deep compressive residual stresses and work hardened layers while retaining a relatively smooth surface finish. In the present investigation, the effect of DR on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) behavior of a Ti–6Al–4V alloy is examined, with particular emphasis on the thermal and mechanical stability of the residual stress states and the near-surface microstructures. Preliminary results on laser shock peened Ti–6Al–4V are also presented for comparison. Particular emphasis is devoted to the question of whether such surface treatments are effective for improving the fatigue properties at elevated temperatures up to ∼450 °C, i.e. at a homologous temperature of ∼0.4T/Tm (where Tm is the melting temperature). Based on cyclic deformation and stress/life (S/N) fatigue behavior, together with the X-ray diffraction and in situ transmission electron microscopy (TEM) observations of the microstructure, it was found that deep rolling can be quite effective in retarding the initiation and initial propagation of fatigue cracks in Ti–6Al–4V at such higher temperatures, despite the almost complete relaxation of the near-surface residual stresses. In the absence of such stresses, it is shown that the near-surface microstructures, which in Ti–6Al–4V consist of a layer of work hardened nanoscale grains, play a critical role in the enhancement of fatigue life by mechanical surface treatment.
For structures made of carbon fiber-reinforced plastics (CFRP), fast, robust, and reliable repair technologies are mandatory for economical usage. In this paper, the authors explain their strategy and experiences. An automated process is proposed to achieve the challenging goals. A general overview on the origin, effects, and analysis of contaminants in CFRP structures and the relationship to the achievable strength of adhesive bonds are given. For the repair of composite structures using adhesive bonding, surface pretreatment is a key factor in terms of reliability and strength. Different surface treatment processes such as grinding, grit blasting, plasma and pulsed lasers treatments are discussed. Furthermore, the possibilities and technical implementation of an automated milling process for the repair of composite structures are presented. This change from manual production to automation tremendously improved the quality and duration of the repair and allows the creation of a uniform surface for adhesive bonding. Further integration of novel technologies is discussed and will further support and enhance the repair in the near future.
The effect of laser-hybrid welds on deformation and failure behaviour of fracture mechanics specimens is investigated in order to provide quantitative prediction of damage tolerance and residual strength. The simulation of crack initiation and crack extension in hybrid welds is performed by applying GTN damage model. The identification of damage parameters requires combined numerical and experimental analyses. The tendency to crack path deviation during crack growth depends strongly on the constraint development at the interface between base and weld metal. In order to quantify the influence of local stress state on the crack path deviation, the initial crack location is varied. Finally, the results from fracture mechanics tests are compared to real component, beam-column-connection, with respect to fracture resistance.
Plastic design allows the exploitation of the full resistance of steel structures by taking advantage of stress–redistributions due to plastic strains exceeding the yield strain. Especially in seismic design the utilization of material reserves and the formation of plastic hinges play an important role. In devastating earthquakes in Northridge (USA) and Kobe (Japan) brittle fracture of welded connections in steel moment frames occurred prior to formation of plastic hinges and utilization of plastic material reserves. The subsequent research works resulted in improved design rules and recommendations for these kinds of failure. But to guarantee sufficient ductile performance of these connections also in the upper shelf region, plastic and earthquake resistant design rules should take into account degradation of strain capacity and toughness properties due to quasi static and especially seismic loading.
In the scope of the current European project “Plastotough”, the main objective is to derive quantified toughness design rules in the upper shelf based on the strain requirements opposed to strain capacities. This paper gives an overview over the research work in performance and shows recent results from experimental and numerical analyses performed within this project for monotonic and cyclic loading.
New calibration method for high and low triaxiality and validation on SENT specimens of API X70
(2013)
The determination of the exact mechanical properties of material is essential for an optimal and safe design of linepipes. It is especially important for the prevention of over-engineering and the reliable assessment of complex accidental loading, such as extreme bending due to loss of buoyancy of support, or abrupt ground movement. Currently, the focus of research in offshore deepwater installations and linepipes is towards pre-cracked structures with high triaxiality stress states and complex loading histories. At the same time, low triaxiality stress states must be correctly studied in order to represent shear dominated failure in pipes. A comprehensive experimental and numerical program was undertaken to determine the mechanical properties of the traditional API X70 grade of steel. The material was characterized for anisotropic plasticity, fracture initiation and uncracked ductility for various states of stress. The same material was also used for pre-cracked fracture toughness assessment. The experimental program included flat and round specimens. The first type of tests on flat butterfly-shaped, central hole, notched and circular disk specimens; were selected to address the low stress triaxiality range. Tests on round notched bar specimens and SENT fracture mechanics tests extended the characterization and verification process to higher stress triaxiality values. This program covered a wide range of stress conditions and demonstrated their effect on the material resistance to crack extension. Each test conducted was numerically simulated using solid finite element models, matching the exact geometric and loading history features. The numerical simulation provided information on the local stress and strain fields around the location of the potential or existing cracks. Based on the above hybrid experimental/numerical technique tailored for pipe applications, the MMC fracture model was calibrated. The model relates the material ductility not only to stress triaxiality but also to the Lode parameter. The predictive capabilities of the MMC were then evaluated in the case of SENT testing, used extensively in the pipeline industry. It was shown that the present fracture model calibration can describe fracture behavior of SENT experiments.
Conventional Selective Laser Sintering of polymers is restricted to the processing of single materials. The fabrication of components consisting of different material regions is a challenge which cannot be realized by standard coating devices basing on blades or rollers. Thus, advanced coating and deposition techniques are needed which enable the precise and reliable control over very small powder quantities in order to prepare arbitrary powder patterns with high accuracy and repeatability. In this report, the delivery of polymer powder by vibrating nozzles inside laser sintering machines is investigated. Therefore, a steel nozzle attached to a piezo actuator is integrated into a machine, whereas the nozzle itself features internal channels which allow the precise control over the powder temperature using heat transfer oil. The setup is used to study the influence of different system configurations on the powder deposition characteristics as resolution and layer surface roughness. The results show that temperature influences the mass flow depending on the material used and that a precise deposition of powder pattern with microscale resolution is possible with optimized parameters. Finally, the multimaterial powder pattern is fused by a new illumination strategy of laser sintering which is called Simultaneous Intensity-Selective Laser Sintering in order to demonstrate the potential of this new approach.
The focus of this paper is the simulation of fatigue crack growth of the coated single crystalline nickel-based superalloy PWA 1484 under thermal mechanical loading. Thus, two physical models are superimposed in terms to firstly calculate the deformation behavior under instationary thermal and mechanical loading (TMF) and secondly to model crack propagation after initial brittle cracking of the coating layer on the basis of cyclic crack tip opening displacement (CTOD). All material parameters implemented in the models were evaluated from monotonic isothermal tensile and creep tests as well as from isothermal low cycle fatigue (LCF) experiments. The calculated fatigue crack growth was validated by in situ crack growth measurements using the beachmark technique. Hence, crack propagation initiated by the brittle coating system closely to the experimental results using rectangular flat specimen geometry instead of corner-crack (CC) specimens. The comparison of the simulated lifetimes to the experimental results provides remarkable accuracy of the physically-based lifetime model.
In diesem Beitrag wird eine Theorie zur taktorientierten Fertigungssteuerung entwickelt. Es wird der kleinste Repräsentant einer taktorientiert gesteuerten Werkstatt ermittelt - das Ein-Ressourcen- Modell. Durch die Modifikation des Trichtermodells kann ein allgemeingültiges Beschreibungsmodell des Produktionsprozesses bei taktorientierter Fertigungssteuerung erarbeitet werden - das taktorientierte Trichtermodell. Es ermöglicht die Darstellung der Arbeitsbestände im aktuellen Bearbeitungstakt und der des nachfolgenden Taktes. Weiter wird das taktbasierte Trichtermodell in ein taktbasiertes Durchlaufdiagramm überführt. Hiermit kann das Bestandsverhalten des Ein-Ressourcen-Modells über der Zeit dargestellt werden. Das optimale Bestandsverhalten pro Takt kann durch ein idealisiertes Durchlaufdiagramm beschrieben werden. Bei realer Auslastung der Ressource entstehen schwankende Arbeitsbestände pro Takt. Hierbei werden durch zu geringe Bestände pro Takt Auslastungsverluste an der Ressource erzeugt. Durch zu hohe Bestände pro Takt entstehen ohne Kapazitätsanpassungen Verspätungen.
Machine allocation planning in job-shop production is challenging due to the high variability of machining times. The tact-time based production control reduces planning effort also the flow of orders in the shop floor is more predictable. This article takes a deeper look at a single production unit controlled tact based. By enhancing the funnel model and looking at the stock behaviour of production units, a deeper understanding of tact-time based production control is gained.
The focus of this paper is the simulation of the thermal-mechanical fatigue behavior (TMF) of two single crystalline Nickel-based superalloys in a temperature range between 400 degrees C and 980 degrees C. The newly developed rhenium-free alloy Astra-3OptW and the rhenium-free alloy CMSX-6 are analyzed concerning the basic deformation mechanisms, i.e. elasticity, time-independent and time-dependent plasticity contributing to hardening. In detail, the relevant parameters for high temperature deformation are identified from isothermal creep experiments and used in a numerical model to simulate the deformation behavior under instationary thermal and mechanical loading. Special attention is focused on the determination of the hardening by the second phase (gamma'-precipitates) and their influence on time-dependent deformation and relaxation mechanisms. Therefore, the parameters describing the stress and temperature dependence of the creep rate (i.e. stress exponent n and activation energy Q) are interpreted in terms of a threshold stress taking into account the hardening contribution of the gamma'-phase. Thus, only a reduced effective stress is active for plastic deformation. Particular attention is focused on the accurate determination of the threshold stress as a function of temperature and applied stress from the Langeborg-Bergmann-plot. The comparison of the simulated TMF-deformation to the experimental TMF-data clearly indicates the accuracy of the model in predicting the resulting stresses induced by instationary thermal and mechanical loading. (C) 2016 Elsevier Ltd. All rights reserved.
In order to understand the absorption characteristic, a ray trace model is developed by taking into account the reflection, absorption and refraction. The ray paths are resolved on a sub-powder grid. For validation, the simulation results are compared to analytic solutions of the irradiation of the laser beam onto a plain surface. In addition, the absorptance, reflectance and transmittance of PA12 powder layers measured by an integration sphere setup are compared with the numerical results of our model. It is shown that the effective penetration depth can be lower than the penetration depth in bulk material for polymer powders and, therefore, can increase the energy density at the powder bed surface. The implications for modeling of the selective laser sintering (SLS) process and the processability of fine powder distributions and high powder bed densities are discussed.
finite element simulation of sheet metal forming, shell elements are widely used. The limits of applicability of the shell elements are sometimes disregarded, which leads to an error in predictions of important values such as springback geometry. The underlying kinematic assumptions of the shell elements do not hold where the thickness of In the metal sheet approaches the value of the radius of curvature. Complex three-dimensional material behavior effects cannot be represented precisely as the result of the simplified kinematics. Here we present a model adaptivity scheme based on a model error indicator. The model-adaptive technique presented in this paper aides to resolve only the critical areas of the structure with a three-dimensional discretization while keeping reasonable computational cost by utilizing shell elements for the rest of the structure. The model error indicator serves as a guide for subsequent automatic adaptive re-meshing of the work-piece followed by a model-adaptive finite element analysis. The accuracy of the approximation obtained by the model-adaptive technique coincides well with that of a more expensive solution obtained with solid elements only.
We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.
The morphology and microstructure of an Al2O3 glass composite (trade name In-Ceram, Vita Zahnfabrik) were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite was produced by infiltration of a lanthanum-based glass throughout a porous Al2O3 body. This alumina body was formed by three classes of particles differing in size and shape: faceted particles typically ≤4 μm in diameter, platelets of average diameter 8 μm, 1.5 μm thickness, and small spheres 0.4 μm in diameter. The outstanding strength properties of the composite (600 MPa, ball-on-ring test) are a result of the high wetting capability of the glass phase on the Al2O3 surface. In addition, plastic strain relaxation in the faceted particles by dislocation formation compensates partially for residual stresses and impedes crack formation at the glass/Al2O3 interface.
In Mensch-Roboter-Arbeitszellen werden Teile eines Produktionsablaufs von einemv Menschen, andere von einem kollaborativen Roboter und wieder andere kooperativvin einem gemeinsamen Arbeitsbereich durchgeführt. Bisher werden das Potenzialvund der Mehrwert dieser Systeme noch nicht ausgeschöpft, weshalb ein systematischer Ansatz zur Definition der Arbeitsabläufe unerlässlich ist. Der Beitrag präsentiert einen iterativen, menschzentrierten Entwicklungszyklus für interaktive Mensch-Roboter-Anwendungen. Dieser Zyklus ergänzt die bisher verwendeten Ansätze der Automatisierung. Er beinhaltet Methoden der virtuellen Realität, um die Arbeitsabläufe iterativ evaluieren und dadurch den Entwicklungsprozess effizient gestalten zu können.
Experimental investigations are conducted to quantify the influence of specimen thickness and orientation on the mechanical properties of selective laser melted stainless steel 316 L. The results indicate that the mechanical strength and ductility increase with increasing specimen thickness until a saturation value is reached from a specimen thickness of about 2 mm. Specimen orientation dependency is pronounced for thin specimens (<1.5 mm), whereas only small deviations in strength are observed for thicker specimens with orientations of 30°, 45° and 90° to build direction. The mechanical properties of the specimen orientation of 0° to build direction shows great deviation to the other orientations and the smallest overall strength. A reliable design of selective laser melted components should account for specimen thickness and orientation, e. g. by a correction factor. Furthermore, it is recommended to avoid loads vertical (90°) and parallel (0°) to build direction to guarantee higher ductility and strength.
We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.
Basalt fabric composite, with different twill wave reinforcements, i.e. twill 2/2 and twill 1/3, have been studied in this work by means of experimental tests and numerical finite element (FE) simulations. As fabric reinforcements show repeating undulations of warp and fill yarn, simple mixtures law cannot be applied.
As a consequence, the mesoscopic scale, lying between the microscopic and the macroscopic one, has to be taken into account to mechanically characterize a fabric reinforced composite. The aim of this work is to evaluate the stiffness of a fabric reinforced composite in warp and fill direction. In particular a numerical FE
model, assuming elliptical sections and sinusoidal shape of the yarns, has been implemented and experimental tests have been carried out in order to validate the proposed model. Finally, the strength and the failure modes le orientation, have been experimentally investigated.
Predicting the core temperature during welding is an ambitious aim in many research works. In this work, a 3D-scanner with integrated pyrometer is characterized and used to measure the temperature during quasi-simultaneous laser transmission welding of polyamide 6. However, due to welding in an overlap configuration, the heat radiation emitted from the joining zone of a laser transmission weld has to pass through the upper polymer, which is itself a semi-transparent emitter. Therefore, the spectral filtering of the heat radiation in the upper polymer is taken into account by calibrating the pyrometer for the measurement task. Thermal process simulations are performed to compare the temperature field with the measured temperature signal. The absorption coefficients of the polymers are measured, in order to get precise results from the computation. The temperature signals during welding are in good agreement with the computed mean temperature inside the detection spot, located in the joining area. This is also true for varying laser power, laser beam diameter and the carbon black content in the lower polymer. Both, the computed mean temperature and the temperature signal are representing the core temperature. In order to evaluate the spatial sensitivity of the measurement system, the emitted heat radiation from both polymers is calculated on basis of the computed temperature field. Hereby it is found, that more than 90 percent of the detected heat radiation comes from the joining area, which is a crucial information for contact-free temperature measurement tasks on semi-transparent polymers.
The generation of multi-material components by laser beam melting (LBM) is a challenge which requires the invention of new coating devices for preparation of arbitrary powder patterns. One solution is the usage of vibration-controlled nozzles for selective deposition of polymer powders. Powder flow can be initiated by vibration enabling a start-stop function without using any mechanical shutter. In this report, the delivery of polymer powder by vibrating nozzles is investigated with respect to their application in LBM machines. Therefore, a steel nozzle attached to a piezo actor and a weighing cell is used in order to measure the stability and time-dependence of the powder mass flow upon vibration excitation with the usage of different kind of powder formulations. The results show that precompression of the powder inside the nozzle by vibration excitation is essential to realize a reliable start-stop function with reproducible discharge cyles and to prevent a initial flush of powder flow. Moreover, the use of different powder materials showed that mass flow is even possible with powders which are not optimized regarding flowability, but is readily enhanced with a factor of 2 to 3 by admixing Aerosil® fumed silica.
LuGre or not LuGre
(2023)
The LuGre model is widely used in the analysis and control of systems with friction. Recently, it has even been made available in the commercial multibody dynamics simulation software system Adams. However, the LuGre model exhibits well-known drawbacks like too low and force rate-dependent break-away forces, drift problems during sticking periods, and significant differences in non-stationary situations between the pre-defined friction law and the one produced by the LuGre model. In the present literature, these problems are supposed to come from the model dynamics or its nonlinear nature. However, most of these drawbacks are not simple side effects of a dynamic friction model but are caused in the LuGre approach, as shown here, by a too simple and inconsistent model of the bristle dynamics. Standard examples and a more practical application demonstrate that the LuGre model is not a “what you see is what you get” approach. A dynamic friction model with accurate bristle dynamics and consistent friction force is set up here. It provides insight into the physical basis of the LuGre model dynamics. However, it results in a nonlinear and implicit differential equation, whose solution will not be easy because of the ambiguity of the friction characteristics. The standard workaround, a static model based on simple regularized characteristics, produces reliable and generally satisfactory results but definitely cannot maintain a stick. The paper presents a second-order dynamic friction model, which may serve as an alternative. It can maintain a stick and produces realistic and reliable results.
Although many composite structures are inconsistently curved, such as the leading edges of aircraft wings, the variety of research in impact engineering is almost limited to the impact performance of plates or cylindrically curved specimens. It is not known whether the findings obtained from standardized tests can be transferred to curved structures or which adaptions are required. Therefore, a deeper understanding of the deformation and damage behavior of inconsistently curved structures is essential to transfer the observed impact behavior of flat specimens to general curved structures and therefore to utilize the full lightweight potential of a load-specific design. An accurate description of the procedure as well as the results of the experimental and numerical study of the low-velocity impact behavior of differently single-curved elliptic specimens is presented. To close the research gap of the impact behavior of geometries with curvatures between the plates and simplified leading edges, novel specimens geometries have been derived from established impact test standards. Glassfiber-reinforced specimens are subjected to an instrumented impact test at constant impact energy. This is numerically investigated by a stacked-layer model, which used cohesive zone modeling to enable the simulation of matrix cracking, fiber fracture and delamination. The resulting projected damage areas, as well as the force and deflection histories, were evaluated and section cuts were examined to discuss the damage morphology, formation and propagation process. Significant effects on maximum deflection, compliance and dynamic behavior on the size and morphology of damage were found.
Die Digitalisierung ist im produzierenden Gewerbe in vielen KMU immer noch schwach ausgeprägt. Viele Unternehmen verfügen nicht über die notwendigen Ressourcen, um das Thema Digitalisierung voranzutreiben. Es dominieren weiterhin die konventionellen Methoden zum Informationsaustausch in der Produktion. Mit dem Low-Cost-Digitalisierungsansatz soll genau für diese Unternehmen die Chance zum Einstieg in die Digitalisierung mit einfachen, aber dennoch effizienten Mitteln ermöglicht werden.
First results regarding the realisation of multi-material components manufactured by Laser Beam Melting of polymers and metals are published. For realising composite structures from polymer powders by additive manufacturing, at first relevant material properties regarding compatibility have to be analysed. The paper shows the main requirements for compatibility between different materials and offers first results in form of a compatibility matrix of possible combinations for composite structures.For achieving gradient properties of additively manufactured metal parts by using composite materials the composition of alloying components in the powder and adapted process strategies are varied. As an alternative to atomizing pre-alloyed materials, mixtures of different powders are investigated.
Obwohl das Laserdurchstrahlschweißen sehr reproduzierbar arbeitet, können Fehler aus den Vorprozessen Compoundieren, Spritzgießen etc. das Schweißergebnis negativ beeinflussen. Dem Anwender steht inzwischen eine breite Palette an Prozessüberwachungsmethoden zur Verfügung, um eine gleich bleibende Produktqualität zu erzielen.
In modernen Produktionen ist Lean Manufacturing einer der wichtigsten Treiber für Produktivitätssteigerungen. Durch neue Entwicklungen im Bereich Industrie 4.0 können Impulse im Lean Manufacturing gegeben werden. An der OTH Regensburg wird getestet, wie kostengünstige Kamerasysteme helfen können, Verschwendungen sichtbar zu machen und zu minimieren. Es zeigt sich, dass auch mit geringen Investitionskosten neue Potentiale zur Verschwendungsreduktion aufgedeckt werden können.
The low-cycle and high-cycle fatigue behavior of the Mg-base wrought alloy AZ31 is investigated in the temperature range 20– 300 °C using total-strain-controlled push – pull tests. It is shown that the mechanical properties of the material are substantially influenced by the direction dependent formation of deformation twins and resulting deformation asymmetry. As a consequence tensile mean stresses develop during total-strain-controlled fatigue tests without mean strain.
Fluctuations of material properties are one reason for the occurrence of cracks and waviness in series production of car body parts. Especially fluctuating tribological conditions have an effect on the friction behavior and thus on the material flow. So far fluctuating material properties are not considered in the standard FE-simulation and consequently not in the tool design. In order to enhance the accuracy of the simulation result and thus improve the tool design regarding a robust process, the appearance of batch fluctuations has to be consistently understood. Therefore, the impact of varying lubricant quantities and roughness have been investigated. Several batches have been analyzed to identify the main influencing parameter regarding the friction behavior. Flat strip-drawing tests have been performed to determine the friction coefficient. The investigations have been performed by using material from the series production, as delivered. Since the amount of lubricant turns out to be the main influencing factor, the characteristics and appearance of the lubricant distribution has been analyzed in a further step. The analysis has shown that the distribution of the lubricant changes within one coil over the coil width and length. In addition, the time of storage has been identified as one main influencing factor on the homogeneity of the lubricant distribution over the coil width. Based on these findings, a method has been developed to map the series production conditions regarding the friction conditions in the simulation. Hence, simulations were performed using a side frame blank with different friction conditions, to investigate the impact on the forming result. The results reveal that by considering realistically existing tribological conditions, more scrap is to be expected compared to the conventional simulation. This leads to the conclusion that previous simulation results are too optimistic. Consequently, the introduced method offers the potential to optimize the tool design by considering fluctuating tribological conditions already in the process of development. Thus, it is possible to reduce scrap and increase productivity.
The movement of a meniscus inside a capillary tube has been extensively studied in the context of displacing one fluid with another immiscible one. This phenomenon exists in many applications including pharmaceutical, oil production, filtration and separation processes, and others. When one of the phases is entrapped inside a capillary tube, it forms what is called a ganglion with two menisci between the two fluids. In a straight uniform capillary tube, a stagnant entrapped ganglion is symmetric. The situation is different if the capillary tube is tapered in which case the two menisci assume different curvatures. Such inhomogeneity of the capillary pressure self-propels the ganglion to move. The fate of the ganglion inside the tapered tube depends on whether it is wetting or nonwetting to the tube wall. That is, after the initial movement, a wetting ganglion accelerates towards the tapered end of the tube while a nonwetting one decelerates towards the wider end before reaching a terminal configuration. Such fates are linked to the variations of the capillary pressure, which continuously increases for a wetting ganglion and decreases for the nonwetting one. In this work, a generalized model is developed that not only describes capillary-driven dynamics over a wide range of viscosity and density contrasts but also pressure-driven scenarios with/without gravity. The model, however, neglects the inertial effect of the two fluids on account of the fact that it is confined to the very early time of the movement process. A first-order nonlinear ordinary differential equation is developed that describes the dynamic behavior of both the wetting and nonwetting ganglions. A fourth-order Runge-Kutta algorithm is developed to solve the model equations. Furthermore, a computational fluid dynamics (CFD) analysis was used to provide a comparison and verification framework.
Maintaining dimensional accuracy is a major challenge of laser powder bed fusion (L-PBF) preventing its application for more complex and filigree L-PBF structures in industrial practice. Previous studies have shown that residual stresses and distortion of benchmark L-PBF components may be predicted by sequential thermo-mechanical analyses. However, the reliability of these analyses for more complex structures must be critically questioned, as comprehensive validation and sensitivity analyses are scarce. In this paper, we present a calibrated and validated low-fidelity sequential thermo-mechanical finite element analysis (FEA) of a tubular L-PBF lattice structure, i.e., an aortic stent, where pronounced local deformation is expected. As a first step, the finite element model was extensively calibrated using experimental data to ensure reproducibility of the simulation results. Thereupon, geometric features critical to the distortion of L-PBF lattice structures and measures to compensate for the distortion, such as inversion of the distorted L-PBF structure, were investigated. It was found that the distortion of the L-PBF lattice structures can be reduced, but not completely prevented, by increasing the strut angles, increasing the strut thickness, and decreasing the transition radius in the area of merging struts. FEA-based inversion of the numerically predicted deformed structure minimized distortion, resulting in the L-PBF aortic stent approximating the intended CAD geometry even with a small strut thickness. This work shows that low-fidelity sequential thermo-mechanical FEA can be used not only for the analysis and deformation compensation of reference structures, but also for the analysis of more complex filigree structures with pronounced local deformation.
One major goal of production system design is to decide on space requirements in the plant. In this phase, detailed information about the supply chain network (e.g. which suppliers deliver which parts) is often unavailable. Nevertheless, typical decisions in supply chain management, like the definition of replenishment processes and quantities or make-or-buy decisions, impact space requirements and the capital investment in raw materials. Therefore, it should be considered in factory and production planning. This research article proposes a simulation approach for a production simulation in which raw material replenishment is integrated to evaluate the capital investment and space requirements for raw materials.
Purpose:
A prepreg production device in laboratory scale is used to develop the production process of unidirectionally reinforced prepregs.
Design/methodology/approach:
The aim of the prepreg production device is to impregnate different types of reinforcement fibers with an arbitrarily selectable thermoset matrix system that completely satisfies the requirements for autoclave processing. As the prepreg production device is designed and built up modularly every module corresponds one step in the process.
Findings:
To identify the parameters of the production process and investigate its sensitivity on the material quality of both the prepreg as an uncured semi-finished product and the composite as the cured material experimental investigations regarding the resin flow, fiber volume content, mass per unit area and void content are carried out. Overall four material combinations have been investigated, where in each case the selected impregnation temperature and the width of the impregnation gap has been reproducibly varied in selected steps.
Research limitations/implications:
The experimental characterization of the prepregs and of the composite material is carried out according to German standards.
The pandemic caused by the SARS-CoV-2 virus has claimed more than 6.5 million lives worldwide. This global challenge has led to accelerated development of highly effective vaccines tied to their ability to elicit a sustained immune response. While numerous studies have focused primarily on the spike (S) protein, less is known about the interior of the virus. Here we propose a methodology that combines several experimental and simulation techniques to elucidate the internal structure and mechanical properties of the SARS-CoV-2 virus. The mechanical response of the virus was analyzed by nanoindentation tests using a novel flat indenter and evaluated in comparison to a conventional sharp tip indentation. The elastic properties of the viral membrane were estimated by analytical solutions, molecular dynamics (MD) simulations on a membrane patch and by a 3D Finite Element (FE)-beam model of the virion's spike protein and membrane molecular structure. The FE-based inverse engineering approach provided a reasonable reproduction of the mechanical response of the virus from the sharp tip indentation and was successfully verified against the flat tip indentation results. The elastic modulus of the viral membrane was estimated in the range of 7-20 MPa. MD simulations showed that the presence of proteins significantly reduces the fracture strength of the membrane patch. However, FE simulations revealed an overall high fracture strength of the virus, with a mechanical behavior similar to the highly ductile behavior of engineering metallic materials. The failure mechanics of the membrane during sharp tip indentation includes progressive damage combined with localized collapse of the membrane due to severe bending. Furthermore, the results support the hypothesis of a close association of the long membrane proteins (M) with membrane-bound hexagonally packed ribonucleoproteins (RNPs). Beyond improved understanding of coronavirus structure, the present findings offer a knowledge base for the development of novel prevention and treatment methods that are independent of the immune system.
Purpose – The purpose of this paper is to demonstrate the processability of cohesive PE-HD particles in laser beam melting processes (LBM) of polymers. Furthermore, we present a characterization method for polymer particles, which can predict the quality of the powder deposition via LBM processes. Design/methodology/approach – This study focuses on the application of dry particle coating processes to increase flowability and bulk density of PE-HD particles. Both has been measured and afterwards validated via powder deposition of PE-HD particles in a LBM machine. Findings – For efficient coating in a dry particle coating process, the PE-HD particles and the attached nanoparticles need to show similar surface chemistry, i.e. both need to behave either hydrophobic or hydrophilic. It is demonstrated that dry particle coating is appropriate to enhance flowability and bulk density of PE-HD particles and hence considerably improves LBM processes and the resulting product quality. Originality/value – At present, in LBM processes mainly polyamide (PA), 12 particles are used, which are so far quite expensive in comparison to, for example, PE-HD particles. This work provides a unique and versatile method for nanoparticulate surface modification which may be applied to a wide variety of materials. After the coating, the particles are applicable for the LBM process. Our results provide a correlation between flowability and bulk density and the resulting product quality.
The Park–Paulino–Roesler (PPR) potential-based model is a cohesive constitutive model formulated to be consistent under a high degree of mode-mixity. Herein, the PPR’s generalization to three-dimensions is detailed, its implementation in a finite element framework is discussed, and its use in single-core and high performance computing (HPC) applications is demonstrated. The PPR model is shown to be an effective constitutive model to account for crack nucleation and propagation in a variety of applications including adhesives, composites, linepipe steel, and microstructures.
Heat staking is a joining technology by which thermoplastic pins are formed by force and temperature to create a form- and force-fitting connection between components. This paper examines the characteristics of 3D printed pins in comparison to conventionally turned pins for heat staking applications. The 3D printed pins are created using fused layer modeling, with variations in horizontal and vertical building directions, as well as different layer thicknesses. The study investigates the impact of significant factors on the heat staking process, including the forming force and temperature. Tensile tests, micrographs, and micro-CT measurements were conducted to determine the properties of the heat-staked joints. Additionally, a stage plan was developed to enhance the understanding of the forming process of both printed and conventionally turned materials. The findings suggest that, under specific process parameters, 3D printed pins exhibit comparable strength to conventionally manufactured pins. The research also demonstrates that the anisotropy resulting from the layer-by-layer construction of the pins significantly influences the strength of the connection. Furthermore, the study reveals that 3D printed pins exhibit good forming accuracy during the heat staking process, and the cavities formed during printing can be substantially reduced.
Kombinationen aus kraft- und formschlüssigen Verbindungen erhöhen die Leistung bei im Hybridguss verbundenen Gussteilen mit Anbau- oder Einlegeteilen und machen separate Fügeprozesse überflüssig. Simulations-Methoden unterstützen das Design kraft- und formschlüssiger Verbindungen. Ergebnisse eines Ausdrückversuchs zeigen eine relativ gute Übereinstimmung zwischen gemessenen und mittels Simulation ermittelten Kraft-Weg-Kurven.
By selective laser sintering (SLS), polymer powders are molten layer by layer to build conventional prototypes or parts in small series with geometrical freedom that cannot be achieved by other manufacturing technologies. The SLS process is mainly defined by the beam–matter interaction between powder material, laser radiation and different material characteristics by itself. However the determination of these different material characteristics is problematic because powder material imposes certain requirements that cannot sufficiently be provided by conventional measurement methods. Hence new fundamental investigation methods to determine the optical and thermal material characteristics like the thermal diffusivity, thermal conductivity, or the influence of different heating rates on the melting behavior are presented in this paper. The different analysis methods altogether improve the process of understanding to allow recommendations for the future process controlling.
AbstractRegularized static friction models have been used successfully for many years. However, they are unable to maintain static friction in detail. For this reason, dynamic friction models have been developed and published in the literature. However, commercial multibody simulation packages such as Adams, RecurDyn, and Simpack have developed their own specific stick-slip models instead of adopting one of the public domain approaches. This article introduces the fundamentals of these commercial models and their behavior from a practical point of view. The stick-slip models were applied to a simple test model and a more sophisticated model of a festoon cable system using their standard parameters.
This paper presents experimental fatigue tests on specially shaped specimens made from quenched and tempered steel 42CrMoS4 and nodular cast iron EN-GJS-600-3. The specimens are geometrically designed to resemble actual subcomponents of forming and cutting dies for sheet metal manufacturing. These subcomponents have failed in the past.Experiments are carried out using a fictive load-time function, which is a modification of an actually measured load curve and has variable mean and amplitude values. This first test series serves as a general validation of a subsequent fatigue analysis. A second test series is carried out with constant mean and amplitude values with a load ratio 𝑅≈0. Here, the load frequencies in the individual test runs are varied between f = 5 Hz and f = 45 Hz in order to investigate the influence of the frequency. Both series are performed on a servo-hydraulic testing machine.The experimental data is then statistically evaluated. The values for the scatter correlate with data from the literature. The data from the test series with the fictive load-time function can thus be used for subsequent validation of a fatigue calculation, which will be addressed in a future publication. Most significant are the findings from the second series of experiments with varied load frequencies, as a significant frequency influence could be detected. Furthermore, the hardening and softening behavior under cyclic loading and the fracture behavior of the materials are analyzed and compared with data from the literature.
Flame sprayed Al-12Si coatings for the improvement of the adhesion of composite casting profiles
(2008)
In this study, flame sprayed Al-12Si coatings were produced on the surface of inlays (aluminum profiles) of composite castings parts. The aim was to enhance the strength between the joining partners inlay and cast. Due to the high surface roughness and the presence of pores in the coatings, combined with the formation of an intermetallic phase at the interface, the adhesion of flame sprayed inlays could be enhanced by a factor of 2 compared to blank inlays and by a factor of 1.3 when compared to sand-blasted inlays. However, results also show that gaps are present, mostly at the interface between the inlays and the flame sprayed coatings, and these gaps have a negative effect on the joining strength of the composite casting parts. Therefore, optimizing the adhesion of the coating on the Al profiles via an improvement in both the sand-blasting and the flame spraying parameters would be beneficial for further enhancement of the adhesion of composite casting parts.
In this paper, the idea of fiber-oriented repair geometries for carbon fiber reinforced plastics (CFRP) is investigated. It considers the differing mechanical properties of unidirectional fiber reinforced material by excluding overlapping regions perpendicular to the fiber direction of the particular layer.
A mechanical and numerical comparison of tensile strength of stepped joints with continuous step lengths per ply and stepped joints with reduced step lengths in plies with fiber orientation differing from load direction is performed.
Finite element simulations show similar shear stresses. Mechanical tests of CFRP laminates with stepped joints show no significant deviation in tensile strength, in spite of a joint length reduction of nearly 40%. This leads to the possibility of a significant reduction of repair area.
Fehlstellen sicher erkennen
(2015)
Manuelle Kommissioniersysteme sind aufgrund ihrer Flexibilität weit verbreitet, jedoch treten bei diesen auch vermehrt Kommissionierfehler auf, die weitreichende Folgen haben können. Deshalb werden zu Beginn des Beitrags die Auswirkungen und Ursachen von Kommissionierfehlern betrachtet. Der Fokus des Beitrags liegt auf der Darlegung von Möglichkeiten zur Fehlervermeidung. Dabei wird ein ganzheitlicher Ansatz verfolgt, der Maßnahmen aus den Handlungsfeldern Technik, Prozess, Organisation und Motivation umfasst. Als Ausblick auf zukünftige technische Hilfsmittel zur Fehlervermeidung wird das Augmented-Reality-unterstützte System Pick-by-Vision aus der Forschung vorgestellt, das wesentliche Vorteile existierender Techniken der Informationsbereitstellung vereinigt.