An η‐compliance method to estimate the J‐Δa curve for pipes with a circumferential surface crack

Abstract

AbstractThis paper presents an η‐compliance method to measure the J‐Δa curve for pipes with a circumferential surface crack, using the experimentally recorded load versus the crack mouth opening displacement (CMOD) relationship. This study modifies the η method commonly practiced for standard through‐thickness fracture specimens to measure the energy release rate, J, from P‐CMOD curve for pipes with a circumferential surface crack. The non‐dimensional parameter η for the surface‐cracked pipes derives from elastic–plastic finite element analyses. The relationship between the crack size and the CMOD‐based compliance, coupled with crack profiles interpolated linearly between the fatigue crack profile and the crack profile after ductile tearing, allows determining the crack depth corresponding to the measured CMOD compliance. The measured location‐specific J‐Δa curves indicate consistency with the fracture resistance curve measured from through‐thickness fracture specimens at small crack extension levels. The difference between the fracture resistances becomes significantly larger as the crack extends beyond 0.5 mm.