Accounting for Microstructure in Large Deformation Models of Polycrystalline Metallic Materials

Microstructures of metallic polycrystalline materials are varied and evolve with mechanical deformation. The influence of microstructure on mechanical behavior is discussed in the context of material model development. Several modeling approaches have been developed over the past 80years which have acknowledged the importance of accounting for microstructural details and these are discussed. Examples of two approaches to the large deformation coupled thermomechanical modeling of metallic materials are presented and their differences are compared. First, a macroscale continuum internal state variable-based model is presented for tantalum, which also allows for damage evolution. Next, a multiscale polycrystal plasticity approach is presented, which explicitly represents the polycrystal aggregate. Experiments necessary for both material parameter evaluation (simple compression tests at different strain rates and temperatures) and model validation (dynamic forced shear) are given and discussed. Results from both modeling approaches are compared against results from the forced shear experiments. Both models predict a temperature increase in the shear zone of the sample of 400K due to plastic work and assuming adiabatic conditions. The continuum model performs better than the mesoscale crystal plasticity approach at predicting the load-displacement responses. Although the single crystal model is 3D, the numerical model is 2D and is believed to be restrictive to the deformation response of the polycrystal. This point-of-view is also supported by comparisons between experimental and predicted crystallographic texture in the shear region. Distributions of vonMises stress, temperature, equivalent plastic strain, and equivalent plastic strain rate in the shear region of the sample as predicted by the polycrystal plasticity model are presented. Simulations like this can assist in our understanding of how materials behave and allow us to develop more physically realistic internal state variable theories for use in engineering applications.