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, ν_H, and that of the flow stress, ν_σ in materials for which elastic deformations are significant. In general, ν_H differs from ν_σ, but the ratio ν_H/ν_σ is found to be a unique function of H/E* where H is the hardness and E* is the modulus relevant to Hertzian contact. ν_H/ν_σ approaches 1 for small H/E*, 0 for large H/E*, and is insensitive to work hardening. The trend in ν_H/ν_σ 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 = k × σ^eff and in which the proportionality factor k is a function of σ^eff/E*.