Shear band development under simple shear and the intrinsicality of strain softening of amorphous glassy polymers

The development of shear bands that induced by localized strain inhomogeneity is a characteristic deformation mechanism and determines ductility of amorphous glassy polymers. To investigate the essence of intrinsic strain softening and its influence on shear band evolution under shearing and reverse shearing, a full-network constitutive model based on the micro-mechanism is implemented into the material point method and finite element method respectively. The results show that the shear band nucleates and propagates in forward shearing, and gradually fades until disappears in following reverse shearing when the specimen regains its original geometry. As reverse shearing proceeds or there is a second forward shearing, the homogeneous plastic deformation occurs preferentially in the previously deformed band but it doesn't display any shear band like the initial forward shearing. It means the glassy polymers undergoing plastic deformation cannot be recovered by reverse straining. In further shearing, new shear bands tend to be initiated outside the existing band and then propagates to merge with the previous band. The initiation and propagation of shear band along the shearing direction is caused by the intrinsic strain softening, independent of loading histories and boundary conditions. The widening of shear band is related to the strain hardening.