The theoretical Mises stress nephogram distribution law of the numerical simulation model of compact tensile specimen under macro state is shown in Figure 1. It can be seen from Figure 1 that except for the crack tip, other areas of the model are outside the stress display range. The stress on the edge and crack surface of the model is small, and there is stress concentration at the crack tip with the maximum stress. The smaller the stress gradient from the crack tip to the outside, the greater the stress gradient at the crack tip than that at both sides of the crack tip. The Mises stress distribution along the fatigue crack is symmetrical.
Under the above conditions, the Mises equivalent stress nephogram of 42CrMo steel compact tensile specimen with crack length of a = 10.02 mm, 14.49 mm, 18.76 mm and 23.24 mm is obtained by simulation when the stress ratio r = 0.1, as shown in Figure 2 below.
When the stress ratio r = 0.6, the Mises equivalent stress nephogram under the condition of crack length a = 10.02 mm, 14.48 mm, 18.71 mm and 26.16 mm is shown in Figure 3.
According to Fig. 2 and Fig. 3, the shape of Mises equivalent stress cloud at the crack tip obtained by numerical simulation is similar to the theoretical value, which preliminarily proves the correctness of solving the stress intensity factor at the crack tip of compact tensile specimen by numerical simulation method.
The Mises equivalent stress nephogram of different crack lengths was obtained by numerical simulation, and the stress concentration appeared at the crack tip. With the increase of the fatigue crack length, the area of Mises equivalent stress cloud at the crack tip is increasing. Under the same crack length, when the stress ratio r = 0.1, the stress at the crack tip is always larger than the stress ratio r = 0.6, which is the same as the conclusion that the stress intensity factor at the crack tip is larger under the condition of small stress ratio.