Theoretical Investigation of the Displacement Burst Observed in Nanoindentation by Collective Dislocation Loops Nucleation Model

Abrupt growth of displacement observed in the relationship between indent load and indent depth in nanoindentation of crystalline materials, so-called displacement burst, has been recognized as one of the representative examples for the nanoplastic behavior. This behavior corresponds to the early stage of the plastic deformation and has greatly been influenced by the collective dislocation emission. In the present paper, we construct the simplified model of the first displacement burst by using the elastic theory based on both the Hertzian contact theory and the classical theory of dislocations to evaluate displacement burst under nanoindentation. As the result of this energetic model, it is found that there is strong correlation between burst width and critical indent depth where dislocation emission occur. Finally, it is shown that more than one hundred high-density dislocations are emitted simultaneously and surface step corresponding to each dislocation causes significant displacement burst.