Modeling and analyzing the complex deformation of thermoplastic polymers

Existing constitutive models rarely considered the effect of transition point from the strain-softening phase to the strain-hardening phase. In this paper, a new phenomenological model is proposed. The model introduces a transition optimization factor to take the effect of the transition point into consideration. The tensile and compressive deformations under different loading conditions are analyzed separately and compared with the results of the DSGZ (Duan-Saigal-Greif-Zimmerman) model. The results indicate that the proposed model is more accurate than the DSGZ model in analyzing the post-yield deformation that possesses a significant transition section. Based on the new stress-strain updating algorithm, a VUMAT subroutine was written for cyclic compression simulations. Comparing with the simulation data of DSGZ model, the proposed model effectively describes the hysteresis loop in the cyclic process. This indicates that the proposed model is more capable of analyzing complex deformations of thermoplastic polymers. Meanwhile, compared with the primal algorithm, the new stress-strain updating algorithm improves the analytical accuracy of the proposed model for the unloading and reloading phases.