The application of fracture mechanics to the impact behaviour of rubber‐toughened polyamides

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Abstract
Rubber‐modification of polyamide is a widely‐applied method of improving material resistance under high strain rate loading. The processing conditions used for preparing such two‐phase blends strongly influence their structure and thus their subsequent impact properties. In the present work the relationships between production parameters, phase structure and impact resistance have been studied, and the rǒle of the rubber phase in promoting energy absorption investigated. It has been found that improved impact resistance, defined as a combination of high resistance to crack initiation and to crack propagation, is achieved by decreasing the polyamide phase viscosity while increasing the extrusion and injection temperatures, the mixing shear rate and the rubber phase volume fraction; an EPR modifier offers superior performance to a polybutadiene modifier; the dominant mechanisms of energy‐absorption are shearing and void formation, there being no clear evidence of crazing; the J‐integral technique of plastic fracture mechanics can be applied to Charpy impact testing; TEM allied with image analysis techniques provides quantitative morphological information on polymer blends.

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