Set of conversion coefficients for extracting uniaxial creep data from pseudo-steady indentation creep test results

Abstract

In the present paper, we show that the uniaxial creep data (i.e., applied stress, σ, and creep rate, ε̇c) can be extracted using a set of conversion coefficients (C1 and C2) obtained from indentation data (i.e., the constant indentation pressure, ps, and constant indentation creep rate, ε̇s) which results in a pseudo-steady deformation state. Finite element simulations showed that sinking-in occurs around an impression for 2≤n<3, whereas piling-up occurs for 3<n≤7, where n is the stress exponent for creep. The change in the surface profile depends only on n. This observation was in agreement with dimensional analysis. Taking into account the altered surface profile, C2(=ε¯̇r/ε̇s), the conversion coefficient for ε¯̇r and ε̇s was found to be constant at 0.20. This value did not depend on n for n=2−7. Here, ε¯̇r is the equivalent plastic strain rate at representative points under the indenter, determined using C1=0.33. ε̇s is the indentation creep rate. The indentation results showed that n=3.3 at T=640K for an Al–1.0mol% Mg solid-solution alloy, and n=4.9 at T=613K and n=6.9 at T=533K for pure Al. For the three cases, values of σ¯r(=C1pc) and ε¯̇r(=C2ε̇s) were extracted from the indentation data using C1=0.33 and C2=0.20. The extracted values were similar to the tensile creep data reported by other researchers. These results support the idea that uniaxial creep data can be extracted from indentation data that exhibits various stress exponents for creep using C1=0.33 and C2=0.20.