An Evaluation of the Critical Nature of Flaws in Plastic Pipeline Gas Distribution Systems

摘要

This grant is advancing the fracture mechanics methodology for describing crack growth. A model is used in which a small area around the crack tip is assumed to act as an ideally plastic solid and the rest of the material as a viscoelastic solid. Two analytical models have been developed and are being compared with experimental results. The strain rate dependency of basic mechanical properties of a polyethylene material typical of that used in gas distribution pipelines has been completed. Creep compliance has been defined using the time-temperature superposition principal. The rate of crack growth as a function of the intensity of the loading has been measured for a high-density, high-molecular-weight polyethylene. The mechanism of fracture in this material has been identified as successive rupturing of the lamellae in the highly deformed region ahead of the crack tip. With the fracture process zone attending the crack tip modeled as an ideally plastic solid and the bulk material modeled as a viscoelastic material, two analytical fracture models for slow stable crack growth in polymers have been developed.