Fracture toughness estimates based on crack opening displacement for circumferential through-wall cracked pipes under combined tension and bending

In order to apply the Leak-Before-Break (LBB) concept to nuclear piping, accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to complex loading, such as combined tension and bending is crucial. In this case, one important element is determination of relevant J-resistance curve for pipes under combined loading. In this respect, this paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and four-point bending, based on the load-Crack Opening Displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic Finite Element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks