Fracture mechanics investigation of crack coalescence in a steel tubular T-joint specimen

Fatigue test of steel tubular T-joint specimens was performed. A beach mark (BM) technique was employed to measure the crack size. Some rare fracture patterns were found. One of the specimens generated two major surface cracks around the weld toe. They were independently propagating at the initial stages and were coalesced into a single surface crack at a certain amount of cyclic loads. Subsequently, the crack was enlarged and became a doubly curved surface crack. Crack propagation (CP) simulation is performed to investigate the fracture behaviors. Extended finite element method (X-FEM) option in an open-source software Code_Aster is used. FEM CP simulation is also performed to validate the X-FEM results. The CP phenomena are carefully examined using the fracture mechanics parameters and crack front trajectories.