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

This paper analyzes the applicability of simple indirect methods for d etermining the impact fracture toughness of ductile polymers. Commerci al rubber-modified thermoplastics were assayed. Tests were carried out in a Charpy impact pendulum on sharp notched samples at room temperat ure and at 80 degrees C. Specimens of different geometric relationship , were considered. Thickness, side grooving and span effects were inve stigated. Results appear to be geometrically and strain rate independe nt ABS and high impact polystyrene samples exhibited a whitening effec t due to craze formation through the whole fracture surface, indicatin g that stable crack propagation was occurring. Medium impact polystyre ne, however, exhibited com bined stable and unstable crack propagation mode, displaying shiny and dull zones on the surfaces of the broken s amples. Data were analyzed following the corrected elastic and the J(c ) methods. The fit quality was evaluated by statistical analysis. In a ddition, two new methods were tried: the methods proposed by Vu-Khanh and De Charentenay for semiductile behavior and by Vu-Khanh for ductil e behavior. The equivalencies between the different critical parameter s that arose from the methods are compared and analyzed.