Failure Orientation in Stretch Forming and Its Correlation with a Polycrystal Plasticity-Based Material Model for a Coll
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NTRODUCTION
SHEET metal forming is an important manufacturing process. It is widely used to produce complex stamped parts from flat blank sheets in the automotive industry. In the last two decades, finite element (FE) simulation has become a powerful technique for the modeling of sheet forming. This reduces the number of trials required for stamping before a model goes into production, which is often quite expensive and time-consuming, and allows the development time for new car models to be shortened. FE simulations have also been used for optimization purposes during the design of sheet metal forming processes. The optimization is achieved using typical constant parameter values, called deterministic optimization. Because the deterministically optimized designs are often highly sensitive to stochastic
YUGUO AN, Principal Researcher, ROMKE BOTERMAN, Researcher, EISSO ATZEMA, Principal Scientist, and MICHAEL ABSPOEL and MARC SCHOLTING, Principal Researchers, are with Application and Engineering, Research and Development, Tata Steel, 1970 CA IJmuiden, The Netherlands. Contact e-mail: [email protected] Manuscript submitted September 28, 2015. Article published online April 25, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
variations in material properties and process conditions, engineers have to introduce certain safety margins that fall below the forming limit diagram.[1,2] However, this approach does not provide any information about the variability of the output results to guarantee a reliable process. In addition, an arbitrary safety margin can lead to either a high scrap rate or expensive material cost. Recently the robust optimization technique has been developed to incorporate process variations and material scatters in the analysis. Based on multiple simulations, the influence and sensitivity of various process parameters and material properties on the forming process can be identified. The resulting output is the identification of the process window and process capability. So the engineers can recognize and anticipate possible problems due to the influence of scatter in an early design stage.[3] Regarding the source of scatter in forming processes, material properties is one of the five dominant factors.[4] The remaining four are loading conditions, boundary and initial conditions, geometry, and uncertainty in the numerical simulation. De Souza and Rolfe discussed a multivariate modeling approach and concluded that the scatter in material properties could have a remarkable effect on spring-back behavior in the stamping processes.[5] Sigvant demonstrated a significant effect of material thickness and strength variation on product VOLUME 47A, JULY 2016—3435
failure of a front side member of a car body.[6] Atzema et al. and Abspoel et al. discussed the characterization and modeling of the stochastic behavior of deep drawing steels. They concluded that engineers were often forced to choose rather simple material models and work with a limited number of material scatter parameters due to the lack of material inf
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