Quasicontinuum simulation of the effect of lotus-type nanocavity on the onset plasticity of single crystal Al during nanoindentation

Stress concentration around nanosized defects such as cavities always leads to plastic deformation and failure of solids. We investigate the effects of depth, size, and shape of a lotus-type nanocavity on onset plasticity of single crystal Al during nanoindentation on a (001) surface using a quasicontinuum method. The results show that the presence of a nanocavity can greatly affect the contact stiffness (S_c) and yield stress (σ_y) of the matrix during nanoindentation. For a circular cavity, the S_c and σ_y gradually increase with the cavity depth. A critical depth can be identified, over which the S_c and σ_y are insensitive to the cavity depth and it is firstly observed that the nucleated dislocations extend into the matrix and form a y-shaped structure. Moreover, the critical depth varies approximately linearly with the indenter size, regarding the same cavity. The S_c almost linearly decreases with the cavity diameter, while the σ_y is slightly affected. For an ellipsoidal cavity, the S_c and σ_y increase with the aspect ratio (AR), while they are less affected when the AR is over 1. Our results shed light in the mechanical behavior of metals with cavities and could also be helpful in designing porous materials and structures.