Article ID: TETSU-2021-066
To enhance the accuracy of sheet forming simulation, applying a material model based on a physical understanding that enables the description of material behavior under multi-axis stress is beneficial. To achieve this, it is necessary to clarify the work hardening behavior of the material under multi-axis stress and its mechanism. It is especially known that steel sheets for deep drawing with an increased r value have different degrees of work hardening under uniaxial and biaxial stresses, which is called anisotropic work hardening. Anisotropic work hardening is considered to be brought about mainly by a texture or dislocation cell structure, but details are unknown. This study thus discusses the physical mechanism using the crystal plasticity finite element method.
The crystal plasticity finite element method was executed with the model that Hoc et al. developed by modeling the accumulation of dislocation. In the analysis, the anisotropic work hardening was reproduced where the equal plastic work surface stuck out around the equal biaxial stress. It is presumed that the anisotropic work hardening occurred because the equal biaxial stress had more slip systems than the uniaxial stress, and eventually had more latent hardening. It was confirmed by changing the crystal orientation virtually that anisotropic work hardening behavior depends strongly on texture. From this, it is concluded that ferrite steel materials have different numbers of active slip systems depending on the texture, and the amount of latent hardening varies accordingly, resulting in anisotropic work hardening.