Environmental stress cracking in uniaxial tension of urethane methacrylate based resins

Constant strain rate tensile tests have been employed to examine the ESC behaviour of cross-linked U/MMA resins in air and two different liquid environments, namely ethanol and petrol. When tested in air at room temperature, the highly cross-linked U/MMA1 resin showed typical brittle behaviour, while U/MMA2 resin, with a lower cross-link density, exhibited some ductility. Both resins failed in a brittle manner when tested in ethanol and petrol, with much lower strengths and strains to failure being recorded in the liquid environments than in air. The severity of ESC attack depended on the relative rate of environmental diffusion into the specimen. Craze-like defects were found only to occur on some samples tested in liquid environments at low strain rate. No samples of either resin showed any evidence of crazing when tested in air. The main effect of cross-linking on ESC behaviour appeared to be restriction of the environmental liquid diffusion into the material.