TY - JOUR A1 - Serrano Munoz, Itziar A1 - Rapontchombo, J. A1 - Magnier, V. A1 - Brunel, F. A1 - Kossman, S. A1 - Dufrénoy, P. T1 - Evolution in microstructure and compression behaviour of a metallic sintered friction material after braking N2 - Due to the complexity of friction materials, the characterization of the tribological properties is prioritised over the bulk material properties even though the tribology is expected to be influenced by the material behaviour. The extent of this relationship is still unknown and further knowledge is required to account for the load history and evolution of the bulk properties. With this view, the compression behaviour and microstructure of a semi-metallic friction material with reduced formulation were investigated before and after a braking program. The thermal loading was monitored with inserted thermocouples. Uniaxial compression tests coupled with Digital Image Correlation (DIC) show significant changes in the worn material, which develops a compression behaviour similar to that of a tri-layered material. The microstructural analysis indicates microcracking of the metallic matrix and carbon diffusion in the Fe-phase. The thermal loading was found to be the key parameter controlling both the friction behaviour and evolution of the material properties. The expected effects of material evolution on the contact uniformity, durability and tribology are discussed. KW - Semi-metallic sintered material KW - Braking load history KW - Uniaxial compression tests KW - Digital image correlation KW - Scanning electron microscopy KW - Evolution of bulk properties PY - 2019 UR - http://www.sciencedirect.com/science/article/pii/S0043164819301735 U6 - https://doi.org/10.1016/j.wear.2019.202947 SN - 0043-1648 VL - 436-437 SP - 202947 PB - Elsevier B.V. AN - OPUS4-48961 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Miccoli, Lorenzo A1 - Silva, R. A. A1 - Oliveira, D. V. A1 - Müller, U. T1 - Static behavior of cob: Experimental testing and finite-element modeling N2 - The aim of this paper is to implement a numerical model to reproduce the nonlinear behavior of cob walls under shear loading. Axial compression, pull-off, and diagonal compression tests were carried out to derive the mechanical parameters. In addition, the stressstrain relationships, the nonlinear behavior, and the failure modes were defined. The experimental results were then used to calibrate a finiteelement model. The material behavior was simulated through a macromodeling approach adopting the total strain rotating crack model. A sensitivity analysis was conducted to assess the effects of varying the parameters with higher uncertainty on the structural behavior. The numerical model achieved good correspondence with the experimental results in terms of simulation of the shear stress–shear strain relationship and of damage pattern. KW - Cob KW - Compression behavior KW - Shear behavior KW - Digital image correlation KW - Finite-element method PY - 2019 U6 - https://doi.org/10.1061/(ASCE)MT.1943-5533.0002638 SN - 0899-1561 SN - 1943-5533 VL - 31 IS - 4 SP - 04019021-1 EP - 04019021-13 PB - ASCE American Society of Civil Engineers AN - OPUS4-47316 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Biegler, P. ED - Marko, A. ED - Graf, B. ED - Rethmeier, Michael T1 - Finite element analysis of in-situ distortion and bulging for an arbitrarily curved additive manufacturing directed energy deposition geometry N2 - With the recent rise in the demand for additive manufacturing (AM), the need for reliable simulation tools to support experimental efforts grows steadily. Computational welding mechanics approaches can simulate the AM processes but are generally not validated for AM-specific effects originating from multiple heating and cooling cycles. To increase confidence in the outcomes and to use numerical simulation reliably, the result quality Needs to be validated against experiments for in-situ and post-process cases. In this article, a validation is demonstrated for a structural thermomechanical simulation model on an arbitrarily curved Directed Energy Deposition (DED)part: at first, the validity of the heat input is ensured and subsequently, the model’s predictive quality for in-situ deformation and the bulging behaviour is investigated. For the in-situ deformations, 3D-Digital Image Correlation measurements are conducted that quantify periodic expansion and shrinkage as they occur. The results show a strong dependency of the local stiffness of the surrounding geometry. The numerical Simulation model is set up in accordance with the experiment and can reproduce the measured 3-dimensional in-situ displacements. Furthermore, the deformations due to removal from the substrate are quantified via 3D-scanning, exhibiting considerable distortions due to stress relaxation. Finally, the prediction of the deformed shape is discussed in regards to bulging simulation: to improve the accuracy of the calculated final shape, a novel Extension of the model relying on the modified stiffness of inactive upper layers is proposed and the experimentally observed bulging could be reproduced in the finite element model. KW - DED KW - Welding simulation KW - Additive manufacturing KW - Dimensional accuracy KW - Digital image correlation PY - 2018 U6 - https://doi.org/10.1016/j.addma.2018.10.006 SN - 2214-8604 SN - 2214-7810 VL - 24 SP - 264 EP - 272 PB - Elsevier AN - OPUS4-47226 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sonntag, Nadja A1 - Skrotzki, Birgit A1 - Stegemann, Robert A1 - Löwe, Peter A1 - Kreutzbruck, M. T1 - The role of surface topography on deformation-induced magnetization under inhomogeneous elastic-plastic deformation N2 - It is widely accepted that the magnetic state of a ferromagnetic material may be irreversibly altered by mechanical loading due to magnetoelastic effects. A novel standardized nondestructive testing (NDT) technique uses weak magnetic stray fields, which are assumed to arise from inhomogeneous deformation, for structural health monitoring (i.e., for detection and assessment of damage). However, the mechanical and microstructural complexity of damage has hitherto only been insufficiently considered. The aim of this study is to discuss the phenomenon of inhomogeneous “self-magnetization” of a polycrystalline ferromagnetic material under inhomogeneous deformation experimentally and with stronger material-mechanical focus. To this end, notched specimens were elastically and plastically deformed. Surface magnetic states were measured by a three-axis giant magnetoresistant (GMR) sensor and were compared with strain field (digital image correlation) and optical topography measurements. It is demonstrated that the stray fields do not solely form due to magnetoelastic effects. Instead, inhomogeneous plastic deformation causes topography, which is one of the main origins for the magnetic stray field formation. Additionally, if not considered, topography may falsify the magnetic signals due to variable lift-off values. The correlation of magnetic vector components with mechanical tensors, particularly for multiaxial stress/strain states and inhomogeneous elastic-plastic deformations remains an issue. KW - Magnetic stray fields KW - Magnetomechanical effect KW - Damage KW - Topography KW - Multiaxial deformation KW - Notch KW - Plastic deformation KW - Metal magnetic memory KW - Digital image correlation KW - Structural steel PY - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-457878 SN - 1996-1944 VL - 11 IS - 9 SP - 1518, 1 EP - 26 PB - MDPI CY - Basel, Switzerland AN - OPUS4-45787 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Daum, Werner A1 - Gründer, Klaus-Peter T1 - VDI/VDE Standardization Activities of DIC Measurement Techniques N2 - With more than 180.000 engineers and scientists VDI Association of German Engineers and VDE Association for Electrical, Electronic & Information Technologies are belonging to the major technical and scientific associations in Europe. Both organizations promote the advancement of technology and among other things by developing recognized technical regulations as national and international standards. Since 2011 Technical Committee 2.15 Optical Measuring Methods for Structure Analysis and Monitoring as a common committee of both organizations is working among other things on the development of standards for optical measuring and testing methods. The committee consists of 27 members representing industrial users, system manufacturers, research institutes and universities. Currently the committee is drafting the new standard VDI/VDE 2626 Part 1 - Optical measuring procedures – Image correlation methods – Basics and equipment, which will be introduced in this presentation. Draft VDI/VDE 2626 Part 1 describes practical acceptance and reverification procedures for the evaluation of the accuracy of optical measuring systems based on digital image correlation (DIC) methods. The document applies to DIC measurement systems used a) for full-field determination of two- or three-dimensional displacement of surfaces, and b) for full-field determination of the elongation or strain of surfaces. The standard describes quality parameters as well as methods and reference objects for their determination. The quality parameters serve to specify DIC systems, and to compare different systems. They are equally suitable a) for acceptance tests as well as b) for reverification of DIC systems within the framework of a quality management system. The acceptance test is used to determine whether the DIC system complies with the quality parameter limits specified by the manufacturer, or with contractually agreed limits by the manufacturer and user, respectively. For this test the quality parameters zero-displacement error, zero-strain error, and displacement error are defined and used. Zero-displacement error and zero-strain error describe minimum measurement uncertainties of the DIC system a user has to reckon with. They are influenced by different uncertainty contributions. The quality parameter displacement error is used to check the ability of the DIC system to determine absolute displacements within the measurement volume and to confirm the traceability of this measurement to the SI system. Reverification of DIC systems serves to ensure long-term compliance with specified limits for the quality parameters. By comparing the results of successive reverification measurements of the quality parameters used for the acceptance test, it is possible to analyze trends with respect to changes in DIC system characteristics. T2 - Annual International DIC Society Conference 2017 CY - Barcelona, Spain DA - 06.11.2017 KW - Digital image correlation KW - Standardization PY - 2017 AN - OPUS4-43373 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pirskawetz, Stephan A1 - Hüsken, Götz A1 - Curosu, I. A1 - Mechtcherine, V. ED - Mechtcherine, V. ED - Slowik, V. ED - Kabele, P. T1 - Combination of Digital Image Correlation and Acoustic Emission for Characterizing Failure Modes in Strain-Hardening Cement-Based Composites (SHCC) N2 - The tensile behavior of strain-hardening cement-based composites (SHCC) is usually investigated on macroscopic scale by means of direct tension tests or bending tests. Additionally, the micromechanical properties of the composites are often described based on single fiber tension and pull-out tests. Such investigations, performed both on macroscopic and microscopic scales, are based on ‘classical’ force and displacement measuring techniques. Advanced test methods such as digital image correlation (DIC) and acoustic emission analysis (AE) may facilitate the identification and the analysis of the failure mechanisms in SHCC, which is important for both monitoring loaded SHCC elements and further material development and optimization. In this study, these two techniques are combined to characterize the failure mechanisms of three different types of SHCC in direct tension tests. The results are related to data of stress and strain measurements. It is shown that DIC provides detailed spatially resolved and stress related strain measurements. Furthermore, it is demonstrated that AE allows for the localization of active cracks, quantification of the damage accumulation under increasing stresses, and characterization of the dominant crack bridging mechanisms and failure modes observed in the different types of SHCC. T2 - 4th International RILEM Conference on Strain-Hardening Cement-Based Composites (SHCC4) CY - Technische Universität Dresden, Germany DA - 18.09.2017 KW - Cementitious composites KW - Strain-hardening KW - Fiber reinforcement KW - Tension KW - Multiple cracking KW - Acoustic emission analysis KW - Digital image correlation PY - 2017 SN - 978-94-024-1194-2 U6 - https://doi.org/10.1007/978-94-024-1194-2 VL - 15 SP - 300 EP - 307 PB - Springer Science+Business Media B.V. CY - Dordrecht, The Netherlands AN - OPUS4-42129 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pirskawetz, Stephan A1 - Hüsken, Götz A1 - Curosu, I. A1 - Mechtcherine, V. T1 - Combination of Digital Image Correlation and Acoustic Emission for Characterizing Failure Modes in SHCC N2 - The tensile behavior of strain-hardening cement-based composites (SHCC) is usually investigated on macroscopic scale by means of direct tension tests or bending tests. Additionally, the micromechanical properties of the composites are often described based on single fiber tension and pull-out tests. Such investigations, performed both on macroscopic and microscopic scales, are based on ‘classical’ force and displacement measuring techniques. Advanced test methods such as digital image correlation (DIC) and acoustic emission analysis (AE) may facilitate the identification and the analysis of the failure mechanisms in SHCC, which is important for both monitoring loaded SHCC elements and further material development and optimization. In this study, these two techniques are combined to characterize the failure mechanisms of three different types of SHCC in direct tension tests. The results are related to data of stress and strain measurements. It is shown that DIC provides detailed spatially resolved and stress related strain measurements. Furthermore, it is demonstrated that AE allows for the localization of active cracks, quantification of the damage accumulation under increasing stresses, and characterization of the dominant crack bridging mechanisms and failure modes observed in the different types of SHCC. T2 - 4th International RILEM Conference on Strain-Hardening Cement-Based Composites (SHCC4) CY - Technische Universität Dresden, Germany DA - 18.09.2017 KW - Cementitious composites KW - Strain-hardening KW - Fiber reinforcement KW - Tension KW - Multiple cracking KW - Acoustic emission analysis KW - Digital image correlation PY - 2017 AN - OPUS4-42132 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Miccoli, Lorenzo A1 - Silva, R. A. A1 - Garofano, A. A1 - Oliveira, D. V. T1 - In-plane behaviour of earthen materials: a numerical comparison between adobe masonry, rammed earth and cob N2 - The paper presents a comparison between different numerical modelling approaches aiming to simulate the in-plain behaviour of three types of earthen materials, namely adobe masonry, rammed earth and cob. For this purpose, uniaxial and diagonal compression tests were carried out, which allowed determining important mechanical parameters, such as compressive strength, Young’s modulus, Poisson’s ratio, shear strength and shear modulus. Furthermore, the tests allowed assessing the level of non-linear behaviour of the respective stress strain relationships as well as the failure modes. The experimental results were then used for the calibration of numerical models (based on the finite element method) for simulating the non-linear behaviour of the earth materials under in-plane shear loading. Both macro- and micro-modelling approaches were considered for this purpose. The procedures adopted for model calibration established the reliability of various modelling strategies for the different loading conditions. The simplified Approach based on macromodelling shows a satisfactory accuracy and low computational costs. The results reproducing the uniaxial compression are in good correspondence with the post-elastic behaviour observed in the experimental campaign. The micro-modelling approach adopted to reproduce the shear behaviour, even with higher computational cost, represents a suitable tool to predict the adobe masonry and rammed earth collapse mechanisms. T2 - COMPDYN 2017 - 6th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering CY - Rhodes Island, Greece DA - 15.06.2017 KW - Earthen materials KW - Compression behaviour KW - Shear behaviour KW - Digital image correlation KW - Finite element method PY - 2017 AN - OPUS4-41002 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Hüsken, Götz A1 - Shamsuddoha, Md A1 - Pirskawetz, Stephan A1 - Baeßler, Matthias A1 - Kühne, Hans-Carsten A1 - Thiele, Marc T1 - Identification of failure pattern in cylindrical grouted connection for wind structures – a pilot study N2 - At present, Wind Turbine Generators (WTGs) operating in onshore and offshore wind farms are primary sources of renewable energy around the world. Cylindrical grouted sleeve connections are usually adopted in these WTG structures to connect the upper structure and foundation for ease of installation. These structures including grouted connections experience considerable adverse loading during their lifetimes. Settlements were reported inside similar connections used in energy structures especially oil and gas platforms, which were installed in last three decades. Thus, repair and rehabilitation of such connections in existing wind structures should also be planned ahead to keep them operating in the future. The nature of failure and crack generation in grouted connections are crucial prior to adopt a strengthening strategy. This pilot study is carried out to actualize the failure mechanism in the grouted connection, when subjected to axial loading. A novel reusable scaled cylindrical grouted connection with shear keys was designed and tested for its load bearing behaviour. The mechanical test was accompanied by classical measuring techniques (e.g. displacement transducer) as well as non-destructive measuring techniques (e.g. digital image correlation (DIC), acoustic emission analysis (AE)). The failure mechanism incorporating slippage of the shear keys and cracking of the grout was investigated. The capacity and applicability of such test mould were also discussed. The knowledge is expected to pave way towards repair of deteriorated grouted connections with similar geometry and failure pattern. T2 - 1st International Conference on Construction Materials for Sustainable Future (CoMS_2017) CY - Zadar, Croatia DA - 19.04.2017 KW - Grouted connections KW - Cracks KW - Failure KW - Strengthening strategy KW - Digital image correlation KW - Acoustic emission analysis PY - 2017 AN - OPUS4-39915 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Shamsuddoha, Md A1 - Baeßler, Matthias A1 - Hüsken, Götz A1 - Pirskawetz, Stephan A1 - Kühne, Hans-Carsten A1 - Thiele, Marc ED - Banjad Pecur, Ivana ED - Baricevic, Ana ED - Stirmer, Nina ED - Bjegovic, Dubravka T1 - Identification of failure pattern in cylindrical grouted connection for wind structures - a pilot study N2 - At present, Wind Turbine Generators (WTGs) operating in onshore and offshore wind farms are primary sources of renewable energy around the world. Cylindrical grouted sleeve connections are usually adopted in these WTG structures to connect the upper structure and foundation for ease of installation. These structures including grouted connections experience considerable adverse loading during their lifetimes. Settlements were reported inside similar connections used in energy structures especially oil and gas platforms, which were installed in last three decades. Thus, repair and rehabilitation of such connections in existing wind structures should also be planned ahead to keep them operating in the future. The nature of failure and crack generation in grouted connections are crucial prior to adopt a strengthening strategy. This pilot study is carried out to actualize the failure mechanism in the grouted connection, when subjected to axial loading. A novel reusable scaled cylindrical grouted connection with shear keys was designed and tested for its load bearing behaviour. The mechanical test was accompanied by classical measuring techniques (e.g. displacement transducer) as well as non-destructive measuring techniques (e.g. digital image correlation (DIC), acoustic emission analysis (AE)). The failure mechanism incorporating slippage of the shear keys and cracking of the grout was investigated. The capacity and applicability of such test mould were also discussed. The knowledge is expected to pave way towards repair of deteriorated grouted connections with similar geometry and failure pattern. T2 - 1st International Conference on Construction Materials for Sustainable Future (CoMS_2017) CY - Zadar, Croatia DA - 19.04.2017 KW - Grouted connections KW - Cracks KW - Failure KW - Strengthening strategy KW - Digital image correlation KW - Acoustic emission analysis PY - 2017 SN - 978-953-8168-04-8 SP - 544 EP - 551 AN - OPUS4-39914 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -