An Effective Area Considering the Principal Stress to Evaluate Creep Strain Measured by Indentation Test

A method to estimate the creep properties by measuring the micro size deformation is required for the FEM analysis considering the creep deformation of the solder joint in-situ. An indentation creep test is one of the effective methods to directly evaluate the creep deformation of solder joint. However, the indentation test does not give the same creep properties as those obtained by the uniaxial creep tests using a bulk specimen. The authors have proposed an indentation test conducted under the constant depth to determine a suitable reference area, which leads to the same creep characteristics as those obtained by the uniaxial creep test. One of the remaining problems of the indentation test is that the reference area cannot be determined without the creep data obtained by the uniaxial creep test using bulk specimens. In this paper, a series of numerical indentation tests under a constant depth were conducted to construct a method to determine a new reference area without creep data obtained from the uniaxial creep test using bulk specimens. The numerical tests were conducted using finite element method (FEM). The numerical tests showed that the distribution of the principal stress plays an important role to determine the reference area of the indentation tests. Finally, it was found that the reference area obtained considering the distribution of the principal stress gives almost the same creep characteristic as those obtained by the uniaxial creep using bulk specimens.