Variations of effective length of the hot torsion test specimen with deformation

Determination of the effective length for the hot torsion test specimen is of great importance to both numerical and closed form solutions and post-processing of the test. Existing methods for calculation of the effective length need much improvement. Based on a concept of equivalent strain energy, a numerical method is presented in this article for determination of the specimenʹs effective length. A priori known/assumed mathematical expression for the constitutive equation is not needed for this method and therefore it can be applied for a wide range of materials with different constitutive behaviors. Linear parametric modeling of the data is used here to estimate instantaneous changes of hardening indices with deformation. The method is applied to the hot torsion test data of X65 micro-alloyed steel. It is shown that the effective length depends on deformation path and changes significantly at the beginning of deformation.