Prediction of the Constitutive Equation for Uniaxial Creep of a Power-Law Material through Microindentation Testing and Modeling

Indentation creep tests and finite element simulations were performed on a model material to show that a constitutive equation for conventional uniaxial creep can be derived using the instrumented indentation testing technique. When the indentation pressure and the indentation creep rate maintain constant values of ps and · ein(s), respectively, the contours of the equivalent stress and the equivalent plastic strain rate in the region beneath the conical indenter expand according to the increase in the indenter displacement while maintaining the geometrical selfsimilarity. These findings indicate that a pseudosteady state deformation takes place around the indenter tip. The representative point exhibiting the creep behavior within the limited region, which actually determines the indenter velocity, is defined as the location where the equivalent stress š sr is equal to ps/3. The equivalent plastic strain rate š_ er at this point is found to be · ein(s)/3.6 in the case that the creep stress exponent is 3. The stress exponent and the activation energy for creep extracted from the results of Al5.3 molMg solidsolution alloy indentation tests are in close agreement with those of tensile creep tests reported in the literature. In addition, the values for š sr and š_ er agree well with the values for the applied stress and the corresponding creep rate in tensile creep tests at the same temperature. The above results show not only that the creep characteristics of advanced materials, which are often available in minute quantities or as smallvolume specimens, can be obtained from carefully designed indentation creep tests, but also that the constitutive equation for tensile creep can be predicted with sufficient precision through indentation creep test results.