Creep characterization of power-law materials through pseudo-steady indentation tests and numerical simulations

Abstract

A constant-indentation creep rate test (CICRT) has been carried out for an Al-Mg solid-solution alloy using a microindenter in the temperature range of 636–773 K. When a conical indenter is pressed into the specimen surface under a load condition of F=F0 exp(γt) (F the indentation load, F0 the initial load, γ the loading rate parameter, t the loading time), the indentation pressure and indentation creep rate approach constant values of ps and ϵ̇in(s), respectively. The representative points of the deformation in the underlying material are defined on a contour line of the equivalent stress σr = C1ps, where C1 is the so-called constraint coefficient of 1/3 reported by Tabor. The finite element simulation of a power-law material subjected to the CICRT shows that the relationship between the equivalent plastic strain rate ϵ̇r at these points and ϵ̇in(s) is ϵ̇r=C2ϵ̇in(s) and that C2 ≊ 1/3.6 in the case of a creep stress exponent of 3.0. The constitutive equation of ϵ̇r versus σr obtained from experimental data and the computed value of C2 is in good agreement with that evaluated from conventional uniaxial creep tests.