A study was made of the effect, of a very small surface step, upon the mechanics of contact in indentation using linear continuum elasticity. Surface steps were shown to lead to a loss of contact in the vicinity of the surface steps as well as a singular contact pressure distribution. This singularity existed for any finite surface step height and led to shear stress concentration in the bulk material that declines in proportion to the inverse of distance from the surface step. This concentration facilitates the nucleation of dislocations and lowered the threshold for onset of plasticity in nano-indentation.

Surface Steps Lead to Heterogeneous Contact Mechanics and Facilitate Dislocation Nucleation in Nanoindentation. M.R.Shankar: Applied Physics Letters, 2007, 90[17], 171924