Evaluation of the Stress Intensity Factor of Brittle Polymers Based on the Crack Arrest Concept

One of the commonly used criteria for characterizing the fracture resistance of brittle glassy polymers or their composites is the critical stress intensity factor or crack resistance. Specimen geometries such as single edge notch (SEN), compact tension, and three-point bend etc., are conventionally used for this purpose. On this basis, the critical stress intensity factor is evaluated at the onset of crack propagation by using the length of the initial notch. Plastics in general experience a slow crack growth regime before the avalanche-like fracture, which is not taken into consideration in the calculation of the critical stress intensity factor. Hence, serious errors are encountered in the evaluation of the resistance of plastics to crack propagation based on the critical stress intensity factor concept, when standard test geometries are employed.