Transferability of specimen J–R curve to straight pipes with throughwall circumferential flaws

Abstract

The stress triaxiality is an important parameter in explaining the geometry dependence of J–R curves. By comparing the stress triaxiality across the ligament of a specimen and a cracked component, it is possible to assess whether the cracked component exhibits similar fracture behaviour to the specimen. In the present investigation, fracture experiments have been carried out on throughwall circumferentially cracked 8-in. diameter pipes under four point bending load and three point bend bar (TPBB) specimens machined from the same pipe. Subsequently, 3-D elastic–plastic finite element analyses have been carried out on cracked pipes and TPBB specimens to determine the stress triaxiality across the ligament. It is found that the stress triaxiality conditions across the ligament are similar for the specimen and the cracked pipes. Therefore, the specimen fracture parameters can be transferred to these cracked components. It is also verified from the experimental results that the specimen J–R curves also fall within the acceptable band of component J–R curves. These investigations emphasise the role of stress triaxiality in selecting the specimen type for transferring fracture parameters under large scale yielding.