The research on the method of compound mode crack propagation is mainly through numerical simulation and experimental research. For the numerical simulation of the propagation path of compound mode crack, Smith and Cooper 1541 initially used the finite element method to simulate the propagation of mode I plane fatigue crack. Sumi and Yang 1551 studied the propagation of two-dimensional composite mode cracks by the finite element method with highly automatic mesh generation. Sumi and Wang obtained the smooth crack growth trajectory by automatic mesh generation technology. Portera1571 analyzed the numerical simulation of two-dimensional and three-dimensional composite crack propagation by dual boundary integral equation. Reimers simulated the calculation of fatigue growth of I-II composite mode crack. Yuan Zhen et al. Arranged meshless elements near the crack tip, and simulated the crack propagation path in other areas by finite element method.
Wang Minge et al. Studied the crack propagation behavior of stainless steel under composite loading. The results show that the crack only changes the propagation direction at the corner or branch of the crack and under the condition of two-way load in the same direction; When the bidirectional load is reversed, the crack only branches. Dong Shiming et al. Studied and analyzed the fracture behavior of PMMA under composite mode loading. The results show that the crack propagates self similarly under pure mode I loading, and the crack propagates non self similarly under pure mode II and composite loading, and the crack begins at the corner of the notch edge.
Ma Shixiang et al. Also carried out crack experimental research under composite mode load. The results show that the closer the load is to mode II and the faster the crack growth is under the condition of equal initial stress field at the crack tip. The results of this experiment are similar to those obtained by Lida and kobayashils. Lebrand and Jean Baptiste studied the crack propagation path under I + III and I + II + III combined mode loads respectively, and obtained that when the crack end extends to the crack propagation direction, the crack gradually twists and reaches the pure opening state.
Qian Shiqiang and others’ influence conditions on the initial cracking angle and crack trend of the composite crack. Since the beginning of the crack propagates in a multi-source manner, several steps at a certain angle to the crack surface are formed first, and the subsequent expansion of the crack mainly depends on the connection of steps and steps. The crack will turn to mode I propagation direction with the decrease of step. Kim analyzed the fatigue crack propagation behavior under I + III composite mode load through experiments. During the fatigue test, it was 0 degrees, 15 degrees, 30 degrees and 45 degrees perpendicular to the unidirectional loading direction respectively. During the experiment, branch cracks and coplanar cracks were observed. It was concluded that coplanar cracks become the main cracks when the mode I stress intensity factor is large.