The strain-rate sensitivity of the hardness in indentation creep

Finite element analysis is used to simulate indentation creep experiments with a cone-shaped indenter. The purpose of the work is to help identify the relationship between the strain-rate sensitivity of the hardness, nu(H), and that of the flow stress, nu(sigma) in materials for which elastic deformations are significant. In general, nu(H) differs from v, but the ratio nu(H)/nu(sigma) is found to be a unique function of H/E* where H is the hardness and E* is the modulus relevant to Hertzian contact. nu(H)/nu(sigma) approaches 1 for small H/E*, 0 for large H/E*, and is insensitive to work hardening. The trend in nu(H)/nu(sigma) as a function of H/E* can be explained based on a generalized analysis of Tabor's relation in which hardness is proportional to the flow stress H = kx sigma(eff) and in which the proportionality factor k is a function of sigma(eff)/E*.