Fracture behavior of mismatching welded joint with surface crack

The surface crack fracture toughness of the base metal,weld seam and HAZ of undermatching welded joint of two kinds of ultra-high strength steel were tested.The fracture toughness probability distribution of base metal and HAZ was compared.At the same time,the finite element method(FEM) was used to analyze the effects of strength matching factor and the crack location on stress field of crack tip and stress triaxiality.The result shows that,while the crack locates in the HAZ,the fracture toughness of HAZ is better than that of the base metal,because the low strength seam reduces stress triaxiality of HAZ.On the other hand,while the crack locate in weld seam,the higher the strength matching factor is and the farther it is to the fusion line,the lower the stress triaxiality,so the better the fracture toughness.When the crack locate in the weld seam center,the fracture toughness of the two matching is quite.