Studies of Creep and Fatigue Crack Growth in HD-PE pipe materials

摘要

An experimental observation and an approach to thermodynamic modeling of creep and fatigue crack growth (CCG and FCG) in High Density Polyethylene (HDPE) is reported in this work. The experimental investigation was carried out at elevated temperatures (80℃) using the Tapered Double Cantilever Beam (TDCB) test specimen allowing the observation of crack growth at constant stress intensity factors (SIF). Both, stepwise and continuous crack growth was recorded with a regular and highly reproducible pattern of crack growth after initiation. The continuous vs. discontinuous crack growth is observed to be dependent on R-ratio. The observations provide the basic data for thermodynamic analysis and application of crack layer (CL) approach to modeling of the fracture propagation process. The thermodynamic forces responsible for process zone (PZ) formation and crack growth are computed as the derivative from Gibbs potential of loaded TDCB specimen with respect to PZ and crack characteristic sizes respectively. A comparative analysis of CCG and FCG suggests a rather complex relation between the two that is not as simple as commonly assumed.