Abstract
In this work, the initiation and stabilization of the Plastic Instability of High-Density Polyethylene have been experimentally investigated and analyzed. Tensile tests using several complex loading paths involving large deformation have been carried out in order to determine the effect of different constant strain rates and various specimen orientations of extruded HDPE sheet on the elasto-viscoplastic behavior during necking. This work also examines the evolution of Poisson's ratio and Modulus of elasticity of semicrystalline polymers due to phenomenon of damage during instability stage. Based on the Considère criterion, a modified instability criterion is proposed taking into account the significant effect of volume variation due to damage under large deformation. The ability of the modified criterion to predict 1st and 2nd Considère strain of this polymer is examined. A good agreement between the modified criterion and the available experimental data is attained. This criterion is also discussed in relation to the orientation behavior and strain rate