Abstract
Accurate modeling of plastic deformation in metals is crucial for improving metal-forming processes and predicting material behavior under complex loading conditions. Traditional continuum plasticity models often struggle to capture key phenomena such as material response during strain-path changes, flow instabilities, and microscale mechanisms governing plasticity. This thesis addresses these challenges by leveraging the Crystal Plasticity Finite Element Method (CPFEM) to bridge the gap between microstructural effects and macroscopic material response. With this goal in mind, this study investigates the development of computational tools and methodologies for crystal plasticity simulations, with a primary focus on enhancing our understanding of plastic flow during abrupt strain path changes.
A versatile computational framework was developed to integrate CPFEM simulations with Abaqus, enabling efficient virtual experiments. This framework includes automated model generation, advanced post-processing tools, and systematic approaches to study yield surface evolution and plastic flow behavior. The research encompasses three main areas: (1) Comparison and improving the of efficiency of implicit and explicit CPFEM implementation (2) development of tools for modeling polycrystalline models with complex geometry, with an emphasis on lattice structures, and (3) systematic investigation of elasto-plastic transitions and plastic flow during strain-path changes.
First, the study presents and compares two state-of-the-art implementations of the ratedependent CPFEM for Abaqus/Explicit and Abaqus/Standard. These implementations leverage adaptive substepping and line-search stabilization techniques to enable fast and stable calculations.
Second, the research introduces an open-source Python tool for facilitating CPFEM simulations of polycrystalline complex 3D geometries, while controlling microstructural attributes including grain size and shape. Applied to lattice structures designed for additive manufacturing, the study reveals that the crystallographic texture of the base material significantly influences mechanical behavior, highlighting the interaction between geometric and texture-induced anisotropy in determining overall mechanical performance.
Third, the research develops a framework for analyzing elasto-plastic transitions and plastic flow during strain path changes. Using full-field CPFEM simulations with a stable rate independent crystal plasticity model, the study provides insights into yield surface vertex formation and evolution during deformation. The findings demonstrate that plastic flow direction aligns with the normal to an instantaneous yield surface probed at very small plastic strains, rather than with the conventional yield surface. The research also reveals a nonlinear complex relationship between strain rate and plastic flow direction, contradicting assumptions in current pseudo-corner models. These insights can be valuable for enhancing future continuum plasticity models.
By combining computational advancements with fundamental plasticity theory, this work contributes to the development of more accurate and predictive material models for engineering applications, while providing practical tools for both fundamental research and engineering applications. The open-source nature of the implementations promotes reproducibility and accessibility for the broader materials science and engineering community.
A versatile computational framework was developed to integrate CPFEM simulations with Abaqus, enabling efficient virtual experiments. This framework includes automated model generation, advanced post-processing tools, and systematic approaches to study yield surface evolution and plastic flow behavior. The research encompasses three main areas: (1) Comparison and improving the of efficiency of implicit and explicit CPFEM implementation (2) development of tools for modeling polycrystalline models with complex geometry, with an emphasis on lattice structures, and (3) systematic investigation of elasto-plastic transitions and plastic flow during strain-path changes.
First, the study presents and compares two state-of-the-art implementations of the ratedependent CPFEM for Abaqus/Explicit and Abaqus/Standard. These implementations leverage adaptive substepping and line-search stabilization techniques to enable fast and stable calculations.
Second, the research introduces an open-source Python tool for facilitating CPFEM simulations of polycrystalline complex 3D geometries, while controlling microstructural attributes including grain size and shape. Applied to lattice structures designed for additive manufacturing, the study reveals that the crystallographic texture of the base material significantly influences mechanical behavior, highlighting the interaction between geometric and texture-induced anisotropy in determining overall mechanical performance.
Third, the research develops a framework for analyzing elasto-plastic transitions and plastic flow during strain path changes. Using full-field CPFEM simulations with a stable rate independent crystal plasticity model, the study provides insights into yield surface vertex formation and evolution during deformation. The findings demonstrate that plastic flow direction aligns with the normal to an instantaneous yield surface probed at very small plastic strains, rather than with the conventional yield surface. The research also reveals a nonlinear complex relationship between strain rate and plastic flow direction, contradicting assumptions in current pseudo-corner models. These insights can be valuable for enhancing future continuum plasticity models.
By combining computational advancements with fundamental plasticity theory, this work contributes to the development of more accurate and predictive material models for engineering applications, while providing practical tools for both fundamental research and engineering applications. The open-source nature of the implementations promotes reproducibility and accessibility for the broader materials science and engineering community.