Estimation of creep constitutive equation by creep indentation test using cylindrical indenter

The creep exponent, n, and creep coefficient, k, in Norton's law characterizes the creep deformation of a high-temperature material. For identifying the creep constants, the uniaxial creep test is generally conducted. However, it is required to prepare many round-type cylindrical specimens. As an alternative to the uniaxial creep test, we proposed the indentation creep test using a spherical ball. However, this creep test has to be interrupted to evaluate the progression of impression size with dwelling time. To prevent the need for such complicated procedure, a simple estimation method based on the indentation creep test using a cylindrical indenter was developed in this study. This method allows us to directly estimate the creep constants from the relationship between impression pressure and penetration rate, which can be continuously measured during testing. A fundamental formula was derived in this study based on a cavity model introduced by Johnson, and it was subsequently corrected using finite element analysis. To check verification of this method, the creep indentation test was conducted on pure aluminum A1050 plates using a cylindrical alumina indenter. It was confirmed that the creep constants estimated from the developed method perfectly coincide with those estimated by conventional methods such as the uniaxial creep and ball indentation tests. Furthermore, it was inferred that the testing procedure of the developed method is simpler than those of the other methods, which is an advantage of usage of this method.