Geometrically Necessary Dislocation Density and Nanoindentation Size Effects: An Atomistic Study
Chi-Hua Yu (National Taiwan University), Yi-Pin Chen (National Taiwan University), Chuin-Shan Chen (National Taiwan University)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium A
Wed 3:10 - 4:30
CIT 227
We studied the correlation between geometrically necessary dislocation (GND) density and nanoindentation size effects using atomistic simulations. Spherical indenters with their radius from 20Å to 100Å and a Berkovich indenter were exploited to model indentation process in Nickel. Hardness and the total length of geometrically necessary dislocation loops were directly obtained from the atomistic simulations. For spherical indenters, we found that the calculated hardness and the square root of calculated GND density are inversely proportional to the square root of indenter radius. For the Berkovich indenter, the calculated hardness and the square root of calculated GND density are inversely proportional to the square root of indentation depth. Both size effects and correlation between GND density and hardness agreed with the trend predicted by the theory of strain gradient plasticity. We concluded that the well-known indentation size effects based on correlation between GND density and hardness at the micron scale are also valid at the scale of a few nanometers.