2012 Volume 6 Issue 1 Pages 48-60
We utilize the relationship between the shape matrix and strain tensor of calculation cell in Parrinello-Rahman's algorithm, which is used in molecular dynamics (MD) methods, and formulate a strain-controlled MD algorithm based on the finite deformation theory of continuum mechanics. We simulate the atomic behavior in a nano-sized polycrystalline aluminum specimen under two different loading conditions. The first loading condition is a simple shear, and the other is a simple shear after compression, which mimics the loading conditions of actual ECAP processing. Atomic strain measure (ASM) is introduced to investigate the distribution of strain at the atomic scale within the specimen. In both cases, it is observed that grain boundary-structured atoms bordering the dislocation emitted from existing grain boundaries (GB) expand onto the slip plane and develop into a new GB plane, accommodating the rotation of adjacent grains. We propose a possible mechanism for grain refinement under severe plastic deformation. Common neighbor analysis indicates that precompression restricts dislocation emission from the GB. ASM results indicate that this deterioration of dislocation emission is caused by configurational change in the GB region that acts as a dislocation source. That is, preferential accumulation of compressive strain is observed near the GB under compression. In addition, precompression promotes GB sliding.
