The formation of shear bands in polymers is almost inevitable. Shear banding inpolymers has a dual meaning: a precursor to failure and a mechanism for further plastic deformation. Polymers have two major characteristics: softening following yieldingand orientational hardening accompanying the rotation of molecular chains. The former causes the initiation and propagation of shear bands, and the latter causes the lateral growth of shear bands. Constitutive models describing large plastic deformations of polymers are relatively mature, and FE based on such constitutive models successfully simulated the entire process of shear band evolution. Twinning is a plastic deformation mechanism that is as important as slip in hexahedral metals such as Mg and Ti alloys.Early experiments clearly observed the entire process of twinning, namely the three stages of nucleation, propagation and growth. Further studies revealed that nucleation and propagation are inevitably accompanied by stress relaxation (softening). Almost all twinning models have neglected stress relaxation for a long time. This results in the inability to simulate the propagation process of twinning. Inspired by experimental observations and comparisons of shear banding in polymers and twinning in HCPmetals, especially the analysis of the formation mechanisms of the two, we established a constitutive model TNPG that describes the entire process of twin nucleation.propagation and growth. The FE based on the TNPG model numerically reproduced the entire process of twinning. Our recent works focus on the morphology of shear bandsand the interaction between shear bands in polymers under different loading conditions,including plane strain compression, torsion, bending, and tube under internal pressure.The results of these works inspired us to propose a new experimental method forstudying twin interactions.