Pattern Formation in Concurrent Multiscale Simulation: A Breakthrough in Understanding Metal Behavior

Project Overview

Dislocation patterns or cell wall formation are key to understanding the mechanical properties of the materials in which they spontaneously arise, and yet the processing and self-assembly mechanisms leading to their formation continue to baffle experts. Tantalum subjected to shock loading has radical changes to its microstructures as function of grain orientation: cell walls are found in grains oriented in <001> but are suppressed in grains with <011> orientation. Here we use transmission electron microscopy (TEM) and discrete dislocation dynamics (DDD) to demonstrate a new mechanism that is key to the pattern-formation process: a coupling reaction between coplanar dislocations. We present the first large scale DDD simulations exhibiting self-organization of dislocation networks into cell walls in deformed BCC (body centered cubic) metal (tantalum) persisting at strain ɛ=20%. The simulation analysis captures several important features of the dislocation cell pattern effect observed in experiments.

Mission Impact

This project is well aligned to Lawrence Livermore National Laboratory's strategic vision and mission, specifically, its core competencies of advanced materials and manufacturing, high-performance computing, simulation and data science, and high-energy-density science. Results of the project will be useful to understand how to control the manufacturing process to achieve desired microstructures, and eventually improve manufacturing processes to meet NNSA's needs and broader national needs for advanced materials. Lastly, understanding the underlying mechanisms (e.g., formation of defect patterns) of material strengthening effects will be useful to control and design matter subjected to high pressure or temperature.