Study of rotational defects and failure of plastically deformed nanocrystals

• Main Author: Muhammad Irfan Jupri
• Other Authors: Wu Mao See
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/78512
• Institution: Nanyang Technological University

This paper aims to study crack nucleation in nanocrystals due to a twist disclination dipole. Additionally, the critcal twist disclination strength and critical equilibrium crack length upon crack nucleation were also observed. Crack nucleation was predicted by comparing the energy states of uncracked and cracked solids. On the other hand, the critical equilibrium crack length could also be determined. This happens when the equilibrium stable and the equilibrium unstable crack lengths are equal to each other. Computational methods for energy analysis and a Zener crack model were used to conduct this study. According to the energy analysis conducted, cracks can only be nucleated in favourable energy conditions. Furthermore, it was proven in the that both stable and unstable cracks exist. It was hypothesised that crack nucleation, critical twist disclination strength and critical equilibrium crack length are dictated by material, geometrical and loading parameters. The findings of this study suggest that the critical twisting strength decreases with the increasing grain size. On the other hand, the critical equilibrium crack length increases with the grain size. It was also observed that the critical twisting strength increases with the disclination core size. However, the critical equilibrium crack length decreases as the disclination core size increases. It can be argued that the grain size of the crack solid and the disclination core size are inversely proportionate to one another since they have opposing effects on critical twist disclination strength and critical equilibrium crack length.