Fakultät Maschinenbau
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Modelling and simulation of safety relevant Driver Assistance Systems (DAS) and Vehicle Dynamics Controllers (VDC) which act in standard and limit situations lead to increasing accuracy demands in the description of dynamic reactions of tyre contact forces, e.g. For that purpose, first-order approaches are widely applied in this field of vehicle dynamics and handling, which originate from Schlippe & Dietrich, were modified by Pacejka and later on refined by Rill.
The present paper deals with the experimental validation of tyre dynamics approaches as it is widely applied in tyre models for vehicle dynamics and handling. Firstly it gives a brief derivation of two modelling principles regarding the deflection velocity in the considered direction of the tyre’s deformation. This is than followed by a brief description of the performed measurement procedure. From the measurements, a set of model parameters of the considered tyre, depending on different manoeuvre speeds and frequencies, is identified, where no particular fitting parameters for the tyre dynamics are needed. Based on these model parameters, the related dynamic simulations are carried out. The comparisons show that the applied first-order model describes the behaviour quite well within a certain operation range, whereas the second-order approach cannot deliver better results in spite of the longer computational time. However, for investigations within an enlarged frequency range of the steer input and at high slip angles, a more detailed model is recommended.
For the dynamic simulation of on-road vehicles, the model-element "tire/road" is of special importance, according to its influence on the achievable results. Sufficient description of the interaction between tire and road is one of the most challenging tasks of vehicle modeling. Two groups of tire models can be classified: handling models and structural or high-frequency models. Usually, various assumptions are made in modeling vehicles as multibody systems. Therefore, in the interest of balanced modeling, the precision of the complete vehicle model should stand in reasonable relation to the performance of the applied tire model. Handling tire models are characterized by a useful compromise between user friendliness, model complexity, and efficiency in computation time on the one hand, and precision in representation on the other hand. The present paper describes the general approach of the semi-physical tire model TMeasy for vehicle dynamics and handling simulation and its enhancement for bore torque simulation in Version TMeasy 5. A parameter fitting process realized by TESIS DYNAware and the validation of real tire behavior by simulation with DYNA4 is presented. Even with first guess parameters, the TMeasy tire model behaves in a realistic and plausible manner. Parameter estimation is intuitive and datasets from previous model versions can be easily migrated. After parameter fitting, the simulation results correlate well with both the tire test rig and full vehicle measurements. The enhancement of a three-dimensional slip calculation in the latest version does not modify the model behavior for high slip conditions, but improves the results not only for highly dynamic situations but also for low speed maneuvers such as parking.
Effiziente Methode zur Bestimmung von dynamischen strukturellen Belastungen in Großpresswerkzeugen
(2016)
In the forming tools for pressing car body parts, heavy blankholders are used to prevent buckling and wrinkling of the blank. During each press cycle, those large masses need to be lifted, raising thereby the structural dynamic load on the forming tool and on the press. Therefore a detailed knowledge about the forming tool dynamics is essential for an accurate and robust design of forming tools. In this paper, a dynamic finite element method (FEM) simulation of selected automotive forming tool is presented enabling identification of regions of critical stresses. For validation of the simulation results, the kinematic responses of the tool's components are compared with the measurements obtained in an experiment.
Simultaneous Laser Beam Melting of polymers (SLBM) allows the generation of multi-material components,consisting of different thermoplastic polymers, within one additive building process. Besides the common advantagesof conventional Laser Beam Melting (LBM), multi-material components built by SLBM can fulfill different productrequirements like different chemical resistances or haptic material properties within a single part. To achieve suchparts, different powder materials are deposited next to each other and preheated a few degrees below their meltingtemperatures by infrared emitters and laser radiation (λ = 10.60 μm), before in the last step the preheated powdersare molten simultaneously by an additional laser source (λ = 1.94 μm). In this paper, different polymer powders likepolypropylene (PP) and polyamide 12 (PA12) are used for the generation of multi-material specimens. By varyingdifferent building parameters according to a specified design of experiments, their influence on the part properties isanalyzed. Important building parameters are the intensity and the irradiation time of the laser beam used for meltingthe preheated powders. Besides using tensile tests to determine the tensile strength and the elongation at break, theaverage part height in dependence of the energy input is analyzed. The overall aim is to specify the correlationbetween different building parameters regarding the energy deposition on the resulting part properties.
The generation of multi-material components using Laser beam melting (LBM) is a challenge which requires the invention of new coating devices for the 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 even when using powders with low flowability. In this report, the selective deposition 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 is applied, whereas the nozzle itself features internal channels which allow the precise control of the powder temperature using heat transfer oil. The setup is used to study the influence of temperature on the powder mass flow. The results show that, next to the vibration mode, the temperature strongly influences the powder mass flow which is done by affecting the moisture and thus the particle-particle adhesion forces. This shows that a precise control of the powder temperature inside the nozzle is required in order to achieve a constant mass flow and thus a successful application of vibrating nozzles inside LBM machines.
Simultaneous laser beam melting (SLBM) allows the direct realization of multi-material components consisting of different polymer materials by a single Additive Manufacturing (AM) process. To achieve a high compound strength between different materials by adhesive bonding, a common boundary zone based on diffusion of the macromolecules is necessary and thus, both materials needs to be compatible regarding their specific adhesion compatibility. However, by SLBM also incompatible polymers can be processed to multi-material parts. If two incompatible polymers are processed, a positive locking between the different materials is necessary to achieve a connection between the materials. The positive locking results of a random mixture process of the different powder materials during the powder deposition process by a two chamber recoater system, which leads to the forming of undercuts of one material in the other during the melting and recrystallization. In this paper, thermoplastic elastomer (TPE) and polypropylene (PP) powders, which are incompatible, are processed to multi-material specimens. By qualifying basic material properties, their influence on the process and especially on the forming of undercuts in the boundary zone is analyzed. To also allow the analysis of the influence of both material and process parameters on the resulting part properties, tensile test specimens are built and their tensile strength is determined. Additionally, cross sections of the boundary zone are prepared and analyzed by microscope images.
Biomechanik des Alterns
(2016)
Quasi-simultaneous laser transmission welding is a well-known joining technique for thermoplastics and mainly used in the automotive as well as in the medical industry. For process control usually the so called set-path monitoring is used, where the weld is specified as "good" if the irradiation time is inside a defined confidence interval. However, the detection of small-sized gaps or thermal damaged zones is not possible with this technique. The analyzation of the weld seam temperature during welding offers the possibility to overcome this problem. In this approach a 3D-scanner is used instead of a scanner with flat-field optic. By using a pyrometer in combination with a 3D-scanner no color-corrected optic is needed in order to provide that laser- and detection-spot are concentric. Experimental studies on polyethylene T-joints have shown that the quality of the signal is adequate, despite the use of an optical setup with a long working distance and a small optical aperture. The effects on temperature are studied for defects like a gap in the joining zone. Therefore a notch was milled into the absorbent polymer. In case of producing housings for electronic parts the effect of an electrical wire between the joining partners is also investigated. Both defects can be identified by a local temperature deviation even at a feed rate of four meters per second. Furthermore a strategy for signal-processing is demonstrated. By this, remaining defects can be identified. Consequently an online detection of local defects is possible, which makes a dynamic process control feasible.
Tightness is often the main requirement for quasi-simultaneous laser transmission welds. However, remaining gaps cannot be detected by the used set-path monitoring. By using a pyrometer in combination with a 3D-scanner, weld seam interruptions can be localized precisely while welding, due to temperature deviations along the weld contour. To analyze the temperature signal in correlation to the progress of gap-bridging, T-joint samples with predefined gaps are welded. The set-path is measured synchronously. Additionally, the temperature distribution and the influence of the thermal expansion of the polymers are studied by a thermo-mechanical FEM-process simulation. On top of that, the melt blow-out of the welded samples is analyzed using μCT-measurements. The experiments have shown that closing of a gap can be identified reliably by the temperature signal and that the squeezed melt flow into the gap and the thermal expansion in the gap zone accelerates gap-bridging. Furthermore the inserted heat can be adapted in the fault zone, in order to avoid thermal damage.
For the dynamic simulation of on-road vehicles, the model-element “tire/road” is of special importance, according to its influence on the achievable results. Sufficient description of the interaction between tire and road is one of the most challenging tasks of vehicle modeling. Two groups of tire models can be classified: handling models and structural or high-frequency models. Usually, various assumptions are made in modeling vehicles as multibody systems. Therefore, in the interest of balanced modeling, the precision of the complete vehicle model should stand in reasonable relation to the performance of the applied tire model. Handling tire models are characterized by a useful compromise between user friendliness, model complexity, and efficiency in computation time on the one hand, and precision in representation on the other hand.
Um die Lebensqualität und Einsatzfähigkeit von Menschen mit Behinderung oder älteren Menschen zu verbessern, wurde untersucht, inwiefern Gamification-Anwendungen beim Anlernen einer Gestensteuerung geeignet sind. Grundlage des Experiments stellt ein intelligenter Arbeitsplatz (Smart Workbench, SWoB) dar, der Personen bei manuellen Handhabungsaufgaben unterstützt sowie bestimmte Produktionsprozesse teilautomatisiert ausführt. Um die Anlage bedienen zu können, muss im Vorfeld eine Einweisung erfolgen, welche von Menschen oder durch ein Lerntutorial mit Gamification-Elementen zur Motivationssteigerung durchgeführt werden kann. In der Studie wurde untersucht, welche Form des Anleitens aus welchen Gründen von unterschiedlichen Personen eher akzeptiert oder abgelehnt wird.