Coupled modeling of anisotropy variation and damage evolution for high strength steel tubular materials

• Coupling models of anisotropy variation and damage evolution are implemented.
• DSCM is used to characterize piecewise hardening and R variation with large strain.
• Stepwise inverse method is used to calibrate GTN/Lemaitre criteria parameters.
• Significance of coupled models on overall prediction of HSST forming is recognized.

High strength stainless steel tube (HSST) presents promising applications in many clusters as one of key lightweight materials. While, over thinning and further crack in plastic deformation are prone to occur due to limited strain hardening and high yield-strength ratio. To avoid this phenomenon, the accurate prediction of forming limit of HSST needs to be achieved considering uneven deformation induced fracture. Via the digital speckle correlation method (DSCM) based tension, both the diffuse necking limited hardening and the variation of Lankford coefficient R along tube deformation are studied, modeled and coupled into the Hill׳48 anisotropic yield framework; then by replacing the Mises effective stress with the extended Hill׳s anisotropic one and using a stepwise inverse method for damage parameter calibration, both the GTN and Lemaitre ductile fracture criteria (DFCs) coupled with anisotropy evolution are established and numerically implemented; thus, regarding several indexes in cases of uniaxial tension, flaring and mandrel bending of HSST, four individual anisotropic plasticity models and two coupled models are compared and evaluated. Due to considering the interplay between inhomogeneous deformation and damage evolution, the coupling model with the improved anisotropic plasticity provides the most accurate prediction of overall performance in all cases. The significance of the coupling DFCs with the anisotropic plasticity on overall simulation of complex forming processes of tubular materials is thus recognized.