Theoretical and experimental standardization of strain hardening index in tensile deformation

Based on the state equation that stress is a function of strain and strain-rate, the differential constitutive equation during superplastic tensile deformation is deduced, and then the mechanical meaning of the strain hardening index in the equation is interpreted. The constraint equation of strain hardening index is deduced, the strain hardening indexes in typical deformation paths are defined, and their interrelations are obtained. The formulae for measuring, indexes in typical deformation paths and precise measuring methods combined with numerical simulation are deduced. According to them, strain hardening indexes are experimentally measured, and measuring methods & results are elaborately analyzed. The results proved that the strain hardening index is non-constant, and has close relations to the changing rule of strain and deformation path; strain hardening index has also close relations to the also with adopted measuring formula in the given deformation path. Therefore, as strain hardening index is quoted, the corresponding deformation path should be shown clearly; when measuring strain hardening index, the adopted formula should correspond to deformation path.