Analysis for Neck Propagation of Plastic Molding (2): Necking Behavior of Poly (butylene telephthalate) under Uniaxial Drawing

摘要

The load displacement and deformation behavior along with the accompanying changes in surface temperature during neck formation and propagation under tensile loading were investigated for poly (butylenes terephthalate (PBT). A numerical model for PBT molding was developed and the neck deformation behavior under tensile loadings was analyzed by the finite element method (FEM). Numerical results were compared with experimental ones.The experimental results showed that neck formation did not occur immediately after the yield, but instead a homogeneous plastic deformation throughout the test piece proceeded the neck formation and propagation. It was observed that an increase in temperature did not occur before the start of the neck formation. The load-displacement behavior obtained by numerical models could well describe the experimental results when an elastic-plastic model under stable temperature conditions was adopted to describe the necking behavior of the PBT sample. Furthermore, the dependency of strain rate on the neck formation was shown to be affected by the instability of plasticity from the numerical results.