Unstable necking due to deformation softening of polybutylene succinate

Self-oscillating neck propagation of amorphous polybutylene succinate was studied. The neck propagated by regular neck front jumps at the stretching speeds from 0.05 to 1000 mm/min. Self-oscillations at extremely low stretching speeds contradicts to the theory of this phenomenon. The instability of the neck propagation was explained by the deformation softening of the polymer.

Fracture Prediction Simulation for Crystalline Polymer Using Homogenized Molecular Chain Plasticity and Craze Evolution Models

The fracture of ductile polymers occurs on the boundary between the molecular chain-oriented and non-oriented regions after the neck propagation. This behavior is caused by the concentration of craze that is a microscopic damage typically observed in polymers. In addition, it is known that the ductility of polymers decreases both at a high and a low strain rates in comparison with that at a middle one. In this paper, FE simulations are carried out for a crystalline polymer subjected to the tensile load at some strain rates by use of a homogenized molecular chain plasticity model and a craze evolution equation based on the chemical kinetics. Furthermore, failure criteria are proposed from an experiment on fibril strength. A fracture prediction based on the craze accumulation and the failure of fibrils is demonstrated applying the criteria to the numerical results. It is indicated that the fracture occurs at a smaller strain under a high and a low strain rate conditions than under a middle one.