Assessment of finite element analyses of load mode (bending vs. tension) effects for mitigation of judgment on pop-ins caused by splits

•Pop-ins can be simulated by finite element analyses using the nodal release method.•When a pop-in is caused by a split, the load mode bending is severer than or equal to tension.•In the case of a split and a load-drop not exceeding 8%, the pop-in can be regarded as insignificant. During a fracture toughness test on a welded joint, a pop-in accompanied by a load drop may occur prior to final rupture. The currently used standards for conditions to determine whether pop-ins are insignificant vary, and are not prescribed based on adequate physical grounds. Moreover, these standards can be too severe in considering the occurrence of pop-ins as equivalent to a fatal rupture in welded structures. Research to formulate reasonable conditions to assess pop-ins is important to determine whether it is necessary to remake or repair the relevant welded structure. This study reports fracture toughness tests on specimens with pop-ins caused by brittle cracks featuring arrest behavior. The results were simulated through finite element analysis by using a nodal release method, which was implemented when a pop-in occurred owing to split formation, to determine whether the pop-in was significant. From analytical results based on a load mode featuring bending and tension, it was found that the crack opening stress distribution under the bending mode at a load drop of 8% or less was larger than or almost equal to that under the tensile mode. Therefore, if the opening of a brittle crack is arrested during three-point bending fracture toughness tests, it would also be arrested in the welded structures under tensile load. In other words, the results showed that such a pop-in could be regarded as insignificant.