Abstract: Based on the energy density equivalent method, a semi-analytical model of equivalent stress intensity factor for semi-elliptical surface cracked plate under bending was proposed, and the stress intensity factor distributions at different positions on the crack front were obtained by finite element analysis. By assuming the fatigue crack propagation path of semi-elliptic surface crack, a method for predicting surface crack shape was established by the compliance technique. The accuracy of the compliance method was verified by changing the loading ratio to outline the crack front in the fatigue crack propagation test. SA-508 steel was used to test the fatigue growth rate of semi-elliptic surface crack with different initial crack geometric configurations. The results show that the semi-elliptic surface crack shape tends to evolve along a preferred path under fatigue bending load and the path is a/t=1-a/c, the shape of the surface crack shows a fixed evolution trend as crack grows and is not affected by the initial crack size and shape. The crack growth rate at different positions of the surface crack front is significantly different, the growth rate at the surface point is greater than that at the deepest point. When the crack propagates along the preferred path, the difference of initial crack shape and size has little effect on the fatigue crack growth rate of semi-elliptical surface crack, the crack growth rate at the same position is approximately the same.

Key words: semi-elliptical surface cracks, fatigue crack growth rate, stress intensity factor, energy density equivalent, compliance method