Characterisation of Rapid Crack Propagation of PE [PE]

A fracture mechanics based method to characterise rapid crack propagation properties of HDPE pipe resins has been developed. The new method is based on quasi-static finite element analysis solutions of energy release rate and displacement, of a modified single-endnotched bend specimen that minimizes dynamic effects associated with impact testing. Dynamic fracture toughness as a function of crack speed and temperature is measured with a procedure that calculates instantaneous crack length from the experimentally measured increase in specimen compliance during rapid crack propagation. Three HDPE pipe materials were tested with this method. Dynamic fracture toughness increases with crack speed until it reaches a maximum at approximately 150 m/s, but decreases rapidly at faster speeds. Maximum crack speeds measured were in the order of 250 m/s. As expected, dynamic fracture toughness decreases with temperature. Modulus, yield strength, and initiation and propagation impact energies are also calculated. Relationships between the properties and parameters measured are illustrated, which provide a comprehensive understanding of RCP in HDPE, useful for material improvement/development, ranking, screening, quality control, and pressurized pipe performance predictions.