An improved correlation between impression and uniaxial creep

A semiempirical correlation between impression and uniaxial creep has been established by Hyde [Int. J. Mech. Sci. 35, 451 (1993)] using finite element results for materials exhibiting general power-law creep with the stress exponent n in the range 2 ?n? 15. Here, we derive the closed-form solution for a special case of viscoelastic materials, i.e., n=1, subjected to impression creep and obtain the exact correlation between impression and uniaxial creep. This analytical solution serves as a checkpoint for the finite element results. We then perform finite element analyses for the general case to derive a semiempirical correlation, which agrees well with both analytical viscoelastic results and the existing experimental data. Our improved correlation agrees with the correlation of Hyde for n4, and the difference increases with decreasing n for n<4. ? 2006 American Institute of Physics.