3D Analysis of Amorphous Polymers Deformation under Mode I

Abstract Fracture in ductile glassy polymers is usually preceded by noticeable and extensive plastic deformation, as shear yielding takes place in the form of shear bands that are limited by progressive hardening of materials at continuous deformation. In the case of a notched specimen, this induces a noticeable crack blunting before the failure. We use a constitutive law that captures realistically the stress-strain fields of solid glassy polymers. In particular, we account for a rate dependent yield stress followed by intrinsic softening and progressive hardening at continued deformation. We analyzed the 3D crack tip fields around a blunted notch loaded under mode I. With an increasing ratio between thickness versus notch tip radius, the shape of crack tip area evolves from a flame like zone characteristic of plane stress conditions to slip lines when plan strain conditions prevail. For a constitutive law representing the response of polycarbonate, we identified a critical thickness vs notch radius value that indicates the transition between plane stress to plane strain dominant loading conditions. The implication for the geometry necessary to derive material toughness experimentally is pointed out and an examination of the mean stress constraint related to the onset of failure by crazing is reported