INSTRUMENTED CHARPY IMPACT TESTING OF POLYETHYLENE

The impact fracture toughness of a tough high density polyethylene has been studied using both pendulum and instrumented driven ram machines. Load-time traces from the latter have been used to derive a fundamental understanding of the Charpy test, building on results from pendulum tests over a broad range of temperature. The measured G value at peak load was found to be independent of specimen thickness, and characterised the breakdown of a fully developed damage zone at the crack tip. This value could also be derived from G values based on total energy via extrapolation of a plane stress-plane strain sandwich model. A unique relationship was found between G to peak and extent of crack tip damage, from which a lower bound brittle toughness could be derived. Overall, instrumentation of the Charpy test is seen to provide a powerful tool in the understanding of impact behaviour.