DETERMINATION OF FRACTURE-TOUGHNESS IN RUBBER-MODIFIED GLASSY-POLYMERS UNDER IMPACT CONDITIONS

This paper analyzes the applicability of simple indirect methods for determining the impact fracture toughness of ductile polymers. Commercial rubber-modified thermoplastics were assayed. Tests were carried out in a Charpy impact pendulum on sharp notched samples at room temperature and at 80 degrees C. Specimens of different geometric relationship, were considered. Thickness, side grooving and span effects were investigated. Results appear to be geometrically and strain rate independent ABS and high impact polystyrene samples exhibited a whitening effect due to craze formation through the whole fracture surface, indicating that stable crack propagation was occurring. Medium impact polystyrene, however, exhibited com bined stable and unstable crack propagation mode, displaying shiny and dull zones on the surfaces of the broken samples. Data were analyzed following the corrected elastic and the J(c) methods. The fit quality was evaluated by statistical analysis. In addition, two new methods were tried: the methods proposed by Vu-Khanh and De Charentenay for semiductile behavior and by Vu-Khanh for ductile behavior. The equivalencies between the different critical parameters that arose from the methods are compared and analyzed.