Biaxial Fatigue Crack Propagation Research Of Welded Joint Of High Strength Steel

When the pressure shell structure of high strength steel is applied to the submarine, it is subjected to cyclic compression load because of the submergence and floating upward of submarine. The pressure hull structure of high strength steel is a large welding structure of plate and shell, but it is easy to produce fatigue crack in the weld toe under cyclic load because of many reasons. In the early study of fatigue life of structure, the calculation of fatigue life left out the compression part of cyclic load. But some researchers find that the cyclic compression load can make the structure cause fatigue failure and fatigue crack. So the study on the fatigue crack propagation of pressure hull structure of high strength steel under cyclic compression load is very significance.We mainly uses ABAQUS’s secondary development language, Python, to compile the biaxial fatigue crack propagation software in this paper and analyzes the biaxial fatigue crack propagation of two common welding structures, T-welded specimen and butt-welded specimen, in pressure hull structure of high-strength steel. Through the analysis of the fatigue experiment results and stress features of the two welding structures and the calculation of finite element, we predict the orientation of fatigue crack initiation of two welding structures. Meantime, we analyze the biaxial and uniaxial cyclic compression fatigue crack propagations about the two welding structures.Finally, we can admit that the initial crack of welding structure will be produced in weld toe under biaxial cyclic compression load and its orientation will be along the maximum shear stress orientation. Welding structure with initial crack under biaxial cyclic compression load will have the residual tensile stress near the crack tip. The residual tensile stress makes the crack expand. The crack propagation rate is fast in the early, and then with the increase of the fatigue cycle, the residual tensile stress decreases gradually, which makes the crack propagation rate decrease, and tend to level. Finally, the crack propagation stops.