Nanoscale incipient plastic deformation in crystalline metals occurs as the result of the collective motion of dislocations. It was known as “nanoplasticity” and was recognized as the elementary process of the macroscopic deformation. Abrupt increases in indent displacements called displacement bursts were observed in recent nano-indentation experiments; that is, the specific behavior for nanoplasticity. In the present study, experimental tests were first conducted to reduce the unique nature of the nanoscale deformation. Subsequently, large-scale atomistic simulations were performed to predict the incipient plastic deformation and a new discrete dislocation model combined with the boundary element analysis was constructed to capture the collective motion of the dislocations. The present results suggested that the incipient plastic deformation required much higher critical shear stress than the theoretical shear strength due to high compressive stress distribution beneath the indenter, and that the displacement burst was induced by surface rearrangement corresponding to hundreds of dislocation dipoles.

Nanoscale Contact Plasticity of Crystalline Metal: Experiment and Analytical Investigation via Atomistic and Discrete Dislocation Models. T.Tsuru, Y.Shibutani, Y.Kaji: Acta Materialia, 2010, 58[8], 3096-102