@article{HansenWagnerPurretal., author = {Hansen, B. and Wagner, P. and Purr, S. and Merklein, M.}, title = {Investigations of batch fluctuation regarding tribological conditions in series production of car body parts}, series = {International Journal of Material Forming}, volume = {14}, journal = {International Journal of Material Forming}, number = {5}, publisher = {Springer Nature}, doi = {10.1007/s12289-020-01600-w}, pages = {871 -- 884}, abstract = {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.}, language = {en} } @article{HansenHoeblerPurretal., author = {Hansen, B. and Hoebler, Michael and Purr, S. and Meinhardt, J. and Merklein, M.}, title = {Basics for inline measurement of tribological conditions in series production of car body parts}, series = {IOP Conference Series: Materials Science and Engineering}, volume = {651}, journal = {IOP Conference Series: Materials Science and Engineering}, publisher = {IOP Publishing}, doi = {10.1088/1757-899x/651/1/012050}, abstract = {The quality of car body parts in series production is strongly dependent on the tribological behavior. Fluctuating material properties such as the sheet roughness and the amount of lubricant have an influence on the forming process. On the basis of large amounts of data it is possible to investigate the friction behavior in series production and to make process adjustments if required. Therefore, inline measurement systems have a great potential to detect the sheet roughness during the cutting process of blanks in the coil line. Furthermore, contactless systems are advantageous as they do not damage the surface. Nevertheless, the optical measuring is influenced by the lubricant layer on top of the surface. Therefore, the previously unknown impact of the lubricant on the measuring result is investigated. Within this study, stationary optical roughness measurements have been conducted using different amounts of lubricant on hot-dip galvanized EDT steel. The results demonstrate the influence of different amounts of lubricant on the sheet roughness measurement. Hence, it is possible to correct the inline measuring results and gain knowledge of fluctuating surface roughness. In addition, strip drawing test has been carried out to investigate the effect of fluctuating tribological conditions.}, language = {en} } @article{WongRasmussenSimonsenetal., author = {Wong, Christian and Rasmussen, John and Simonsen, Erik B. and Hansen, Lone and de Zee, Mark and Dendorfer, Sebastian}, title = {The Influence of Muscle Forces on the Stress Distribution in the Lumbar Spine}, series = {The Open Spine Journal}, volume = {3}, journal = {The Open Spine Journal}, number = {1}, doi = {10.2174/1876532701103010021}, pages = {21 -- 26}, abstract = {Introduction: Previous studies of bone stresses in the human lumbar spine have relied on simplified models when modeling the spinal musculature, even though muscle forces are likely major contributors to the stresses in the vertebral bones. Detailed musculoskeletal spine models have recently become available and show good correlation with experimental findings. A combined inverse dynamics and finite element analysis study was conducted in the lumbar spine to investigate the effects of muscle forces on a detailed musculoskeletal finite element model of the 4th lumbar vertebral body. Materials and Methodology: The muscle forces were computed with a detailed and validated inverse dynamics musculoskeletal spine model in a lifting situation, and were then applied to an orthotropic finite element model of the 4th lumbar vertebra. The results were compared with those from a simplified load case without muscles. Results: In general the von Mises stress was larger by 30\%, and even higher when looking at the von Mises stress distribution in the superio-anterior and central part of the vertebral body and in the pedicles. Conclusion: The application of spine muscles to a finite element model showed markedly larger von Mises stress responses in the central and anterior part of the vertebral body, which can be tolerated in the young and healthy spine, but it would increase the risk of compression fractures in the elderly, osteoporotic spine.}, subject = {Lendenwirbels{\"a}ule}, language = {en} }