Experimental and numerical study of the method to determine the creep parameters from the indentation creep testing

Abstract

Indentation creep testing and uniaxial creep testing were carried out in this paper in order to set up the relationship between them. The aim of this work is to present a experimental validated method to determine the material creep parameters ( n m, creep stress exponent; c m, creep factor, ε ˙ = c m σ n m , ε ˙ , tensile creep strain rate at the steady state; σ, creep stress, usually from the uniaxial tensile testing) from the indentation creep testing. Aluminum alloy 2A12 was tested in this paper. Firstly, a set of indentation creep testing was carried out at 200 °C with a flat cylindrical indenter. The net indentation creep stresses were between 905.4 and 1414.8 MPa. The steady indentation creep rates in different indentation stresses were obtained, from which the indention creep parameters ( d ˙ = c I σ N n I , d ˙ , the indentation creep depth rate at the steady state; σ N, the net section stress; n I, indentation stress exponent; c I, indentation factor) can be derived. The indentation creep testing was simulated by the finite element method. In order to validate the method, a set of uniaxial tensile creep testing was carried out at the same temperature, i.e. 200 °C. From the uniaxial tensile creep results, the material creep parameters ( ε ˙ = c m σ n m ) were also derived. It is shown that the stress exponent determined from indentation and uniaxial creep testing is same, respectively, at a same temperature. A method has been presented to set up the relationship between the indentation creep parameters ( d ˙ = c I σ N n I ) and uniaxial creep parameters ( ε ˙ = c m σ n m ) based on a conversion factor. With the indentation creep testing results in conjunction with finite element creep analysis, the material creep parameters ( n mI-FEM and c mI-FEM) have also been derived. It can be concluded that the indentation creep testing can been used to determine the creep parameters ( n m and c m). The most important conclusion is that the indentation creep exponent is equal to the material creep exponent, n m = n I.