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

Abstract

This 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.

Measuring J‐R curve under dynamic loading conditions using digital image correlation

“…The standard method requires unloading and reloading to derive the elastic compliance of the specimen, which yields accurate prediction of the crack size and facilitates the J-integral calculation under an η approach. 35,36 However, the elastic compliance measurement is not possible under dynamic conditions as the impact loadings are irreversible. Recent development in digital image correlation (DIC) 37 allows non-contact approaches to evaluate the J-integrals through remote cameras.…”

A node release approach to estimate J‐R curve for single‐edge‐notched tension specimen under reversed loading

“…Ruggieri proposes a η function for the SE(T) specimen made of a homogeneous material, and Parades and Ruggieri evaluate the η factor for the SE(T) with a weld centreline crack. Parool et al calculate the η value for SE(T) specimens and compare the J value based on this η with that from the hybrid method. Cravero and Ruggieri calculate the η and γ factors for clamped and pin‐loaded SE(T) specimens.…”

“…The single specimen technique measures the crack extension through the compliance. Parool et al propose a CMOD‐based compliance versus crack size relationship for the SE(T) specimen. Wang and Omiya suggest a CMOD‐based compliance equation with an effective elastic modulus.…”