Molecular chain plasticity model considering poly-entangled points of molecular chain in glassy polymer and large deformation FE analysis on deformation-induced anisotropy

In the previous paper, a concept of "molecular chain slip system" was newly proposed for glassy polymer by analogy with the crystal plasticity theory for metals. An inelastic response law based on a probabilistic theory considering change of local free volume was adopted as a hardening law. An FE simulation was carried out for PMMA under plane strain tension. Macroscopic neck propagation with high strain rate shear band and directions of molecular chains in the oriented region were computationally visualized. Moreover, a nonlinear viscoelastic behavior was accurately predicted. However, amorphous state in which molecular chains were entangled at random was not expressed appropriately because same initial directions of molecular chains were given to each material point. In addition, elastic isotropy was assumed and change of elastic modulus due to orientation of molecular chains was not considered. In this paper, the extended Taylor model, in which many slip systems are given to a material point and their initial directions are random, is applied to the present theory in order to represent more realistic amorphous state of glassy polymer. Furthermore, anisotropy parameter is defined from dispersion of slip system directions and it is attempted to express an elastic anisotropy induced by molecular chain orientation with plastic deformation, introducing anisotropy parameter into the elastic constitutive equation.