Atomistic-informed Finite Temperature Crystal Plasticity Finite Element Modeling of Body-centered Cubic Single Crystals

Crystal plasticity is a long-standing problem in computational materials. Understandingdeep mechanism of plasticity, such as dislocation, multiplication, interaction, has been a great challenge of major scientific significance since there exist many physical and technical difficulties. It is believed that plasticity in a crystal is strongly influenced by the aggregated dislocations. The aggregated dislocations usually form definite dislocation networks or substrates when plastic loading happens and the networks or substrates are usually called as dislocation patterns. It is commonly known that dislocation patterns and their interactions determine plasticity of crystalline material. Based on lots of experimental observations, it is found that under the same loading and boundary conditions, the specific type of atomic crystal structures usually generates very similar dislocation patterns. Therefore, it is believed that the dislocation patterns emerged in crystalline materials are strongly related to the atomic crystal structures of crystalline materials at the beginning stage of plastic deformation. On the other hand, for metallic materials, especially Body-centered Cubic (BCC) crystal materials, the thermally-activated dislocation glide has a tight link to crystal plasticity, such as constitutive relation (stress-strain curve), screw dislocation glide and temperature-induced Peierls-stress. Because the thermally-activated screw dislocation glide results to thermallyinduced Peierls-stress and yield stress decreasing. In this dissertation, it is developed that a temperature-dependent higher-order Cauchy- Born (THCB) rule for Multiscale Crystal Defects Dynamics (MCDD) of crystalline solids based on harmonic approximation. The THCB rule is employed to develop an atomistic-informed constitutive model and the corresponding higher order stress are used to model crystal plasticity of single crystals. It is shown in the dissertation that the developed finite temperature atomistic-informed crystal plasticity finite element method is able to capture the temperature-dependent dislocation substructure and hence crystal plastic deformation. The main contributions and novelties of the present work are highlighted by following findings: (1) A temperature-dependent higher-order Cauchy-Born rule and an atomistic-informed strain gradient theory have been developed, and the corresponding temperature-related higherorder stress and elastic tensor formulations are derived; (2) The finite temperature MCDD provides an atomistic-informed crystal plasticity finite element method that can simulate anisotropic crystal plasticity in any orientation within the stereographic triangle at micron scale and above; (3) The developed multiscale crystal defect dynamics (MCDD) is able to capture the non-Schmid effects of BCC single crystals; (4) The developed multiscale crystal defects dynamics (MCDD) is able to capture the size effect of single crystal plasticity, and (5) The finite temperature MCDD can simulate the temperature dependent dislocation substructure, and it captures cross-slip in single crystal at low temperature (~ 20K) and captures dislocation cell structures at high temperature (~ 500K).

Advisor: Li, Shaofan