Strain rate sensitivity in nanoindentation creep of hard materials

This paper examines the strain rate sensitivity of the hardness v(H) in relation to the strain rate sensitivity of the flow stress (v,) in hard solids when there is friction between the indenter and specimen. Finite element analysis is used to simulate indentation creep of von Mises solids with a range of hardness/modulus ratios (H/E*) and coefficients of friction, mu, for indenter-specimen contact. We find that, although the level of H is affected by friction, the ratio v(H)/v(sigma) as a function of H/E* remains nearly unchanged. Measurements indicate that v(H) = 0.015 +/- 0.02 for fused silica, from which, based on the present analysis, v(sigma) approximate to 0.022 and from which an activation volume of 0.13 nm(3) can be estimated for plastic deformation.