It was found that the stress-based FLSD differs from the conventional strain-based FLD,and the reasons for the disagreement between them were discussed,the influence of strain hardening index and wall thickness on FLSD was also analyzed.

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 physical meaning and several determination methods of strain hardening index and thick anisotropy index r are introduced.

For the steel containing high content martensite,strain hardening exponent n and strain hardening rate significantly increase in the stage of uniform deformation with the increase of martensite.

The results showed that the strain hardening exponent,determined by the Crussard-Jaoul analysis,was affected by dislocation density and twin volume fraction,especially,it was increased greatly with twin.

With the indication ball indentation technique ( IBIT),the indentation hardness,young\'s modulus,yield strength,ultimate tensile strength,strain hardening exponent and surface residual stress of the tested joint were simultaneously measured.

Through the simulation,the influences of strain hardening exponent n,coefficient of normal anisotropy r and flanging coefficient K on hole-flanging formability were analyzed.