Deviations in yield and ultimate tensile strength estimation with the Small Punch Test: Numerical analysis of pre-straining and Bauschinger effect influence

Abstract

There is a growing interest on the Small Punch Test (SPT) and its many applications in a broad range of industries and sectors. The miniature volume of the SPT specimen eases the mechanical characterization of components and structures when standard tests are impracticable. But this miniature test is limited for one of its more constraining requirements: the material isotropy. Since this test subjects the material to triaxial stress and strain fields, isotropy is necessary to compare the resulted data from SPT with the standard tests, which generally show uniaxial stress fields. Another key element of this question is that initially, isotropic material can lose this property due to a cold pre-straining process and the existence of the Bauschinger effect. In this investigation, a numerical study with the finite element method was performed to understand the influence of pre-straining and the Bauschinger effect in yield strength and ultimate tensile strength estimation with the SPT. This study concludes that in the absence of isotropy, generated by a pre-straining, the SPT estimated a mean value of the principal yield strength components of the yield surface. It is also verified that presence of pre-straining in the SPT specimens invalidated their use to calculate the coefficients of the correlation equations for yield strength estimation.