Transition from Brittle to Ductile Failure in Polyethylenes

摘要

The focus of this thesis is to study the evolution of notch-tip damage to failure of two polyethylenes associated with pipe manufacture, at various stress levels characterizing the competition between brittle and ductile modes of failure. This thesis investigates the failure behavior of polyethylene as the stress is increased, approaching the yield point where failure is in the ductile mode. The mechanical behavior of polyethylene is explored as the transition from brittle failure to ductile failure occurs. This project provides for a continuation of earlier research by studying the characteristics of the failure of polyethylene exposed to stress levels from about one half and up to the yield point. In order to provide a continuity in results, experiments were conducted on Marlex 6006, the same material used in previous research. Also studied was TR 418, a branched polyethylene, typical of the material used in the actual manufacture of gas pipe. The experimental parameters that were varied were stress, notch depth, temperature, and material. Quantitative measurements were made with an optical microscope fitted with a filar objective, a strain guage extensometer, a thermocouple, timer, and a digital data collector.