Essential Work of Fracture Testing Method Applied to Medium Density Polyethylene

Abstract

Thermoplastic polyethylene has been increasingly used in important structural applications, e.g., in the production of pipelines for water and natural gas distribution systems, leading to the growing interest in the characterization of the material's fracture toughness. By virtue of its high ductility at room temperature, elastic-plastic fracture toughness concepts are most convenient for this purpose. In this work, a systematic study about the suitability of Essential Work of Fracture (EWF) test protocol to a medium density polyethylene (MDPE) resin designed for water pipelines extrusion is carried out. The influence of test piece preparation and geometry, along with different pre-cracking methods are investigated and their effects on the obtained results are assessed. It has been concluded that EWF methodology is well applicable for the characterization of MDPE resin and the test parameters allow, for instance, the evaluation of process induced anisotropy effects in the sample and the ranking of in-service mechanical performance of different resin grades. It has also been shown that pre-cracking method, test coupon thickness and processing technology impact the obtained results within 5% statistical significance level and that ‘rougher’ pre-cracking methods affect negatively the test results by increasing data dispersion.