Development New MAT Applied Yoshida 6th Order Yield Function and its Verification

Sheet metal forming simulation has become an indispensable tool for design of automobile parts and process design of its die. As for automobile parts, high strength steel and aluminum alloy are applied for them in progress. On the other hand, these lightweight materials are well known as difficult formability, and many problems have occurred in stamping process. In elasto-plastic FEA, there are many factors that determine the analysis accuracy, the material model is especially important. In case of applying associated flow rule, the yield function is key, and the reproductive capability of the material properties are very significant and influential. In LS-DYNA, there are many material models, and various yield function can be applied. MAT36(Barlet’89), MAT37(Hill’48), MAT242(Ylld2000-2D) [1] are commonly used in sheet metal forming. And this time, the MAT model that uses Yoshida 6th order yield function [2] are developed by using USER MATERIAL function in order to improve the accuracy. This MAT model take Yoshida-Uemori kinematic hardening model which is well known to be able to properly reproduce Bauschinger effect into account. And it can also strain dependency of Young’s modulus into account. This yield function is applicable with 16 parameters both to shell elements as well as solid elements, therefore this model is user-friendly for users from this point of view. In addition, it is easy to consider anisotropic hardening which is important factor for accuracy. This model was implemented as MAT_289. In order to verify the analysis accuracy of this material model, the benchmarks of NUMISHEET 2018 [3] are calculated and the calculation results are compared with experimental data. Good results are also obtaine when shell elements are used and another case where application of solid elements are necessary. In this paper, the analysis results of MAT289 or the other MAT models are compared with experimental results.