Effect of primary creep on the relationship between indentation and uniaxial creep: A theoretical model

Abstract In this work, a theoretical model is developed to address the effect of primary creep on the relationship between indentation and uniaxial creep tests. By considering the expansion of a spherical cavity in the materials following the primary creeping law, a general expression of the conversion factor is deduced during the primary creep stage. For creep tests with spherical and flat punch indenters, a closed-form formula is specified for the conversion factor that is determined by the stress exponent and hardening exponent. By further considering the difference of the critical time at the onset of steady-state creep deformation between uniaxial and indentation creep tests, it becomes available to convert the indentation creep data into uniaxial creep results during the steady-state creep stage. The rationality and accuracy of the proposed model are verified by comparing with the experimental data of Sn37Pb solder, AZ31 Mg alloy and Succinonitrile. Furthermore, the comparison with previous theoretical models indicates that the ignoring of primary creep effect could lead to the deviation of converted indentation creep data from uniaxial creep results.