Summary — Lesson 7

In this course, we discussed the crystal plasticity material model and how to set up and conduct a crystal plasticity analysis from an input microstructure. Let us summarize the key takeaways from each lesson.

Overview of Microstructures and Crystal Plasticity Theory – Lesson 1

• A microstructure contains many grains with different crystal orientations, the interfaces between different grains are known as grain boundaries.
• The size, shape, and preferred crystal orientations of the microstructure affect the mechanical behavior of the material.
• Slip systems are sets of slip planes and slip directions along which dislocation motion can easily occur, and it changes depending on the crystal structure of the material.
• The current crystal plasticity model considers plastic strain induced by mesoscopic crystalline slip on different slip systems of the material.

Problem Specification and Assumptions – Lesson 2

• A microstructure characterization workflow involves producing the stress-strain curve given an input microstructure, relevant material properties, and loading conditions.
• Since the microstructure is oligocrystalline, plane strain condition is assumed.

Microstructure Generation and Meshing – Lesson 3

• Two pieces of information are needed in the voxelated microstructure input file: Grain IDs and Euler angles (for each voxel in the domain).
• Two meshing methods are available for converting the microstructure to a finite element mesh:

1. 1. Convert each voxel to a hexahedral element, robust but with stair-step grain boundaries.
   2. Smooth the grain boundaries and mesh with tetrahedral elements through meshing workflow, beta feature but with smoothed grain boundaries.

• Python scripts are provided to reduce manual preparation effort.
• Linear and quadratic elements are possible during meshing.

Material Assignment for Microstructures – Lesson 4

• Material assignment for both types of meshes is handled automatically by the preprocessing Python script.
• Material properties for Aluminum 2024 T3 were used in this course, and the material properties for Copper were provided.
• The Python script produces a .dat file containing APDL commands for crystal plasticity material assignment later used by the solver.

Crystal Plasticity Analysis in Ansys Mechanical – Lesson 5

• Meshes are introduced to the Static Structural block as External Models.
• Dummy material assignment needs to be assigned to all imported bodies.
• Large deflection needs to be turned on for crystal plasticity.
• Insert an APDL command snippet in the Solution module for crystal plasticity material assignment.
• The process of adding boundary conditions and post-processing the results are identical to regular structural analyses in Mechanical.
• The stress-strain curves from both meshes differ as plastic strain develops, but can be attributed to the coarse mesh and linear tetrahedral elements used in this course, which lead to an overly stiff solution with the linear tetrahedral mesh.

Crystal Plasticity Analysis in PyMAPDL – Lesson 6

• The crystal plasticity analysis shown in Lesson 5 can be completed within Python without opening any GUIs.
• The Python-based solution is suitable for automated parametric study or being a part of a larger automated simulation workflow.
• Post-processing and visualization can also be done in Python.