In order to verify the accuracy of the fatigue crack growth test of the compact tensile specimen, the data of crack length and stress intensity factor at the crack tip obtained by numerical simulation and test are plotted and fitted in origin software. It can be seen that when the stress ratio r = 0.6, the process of fatigue crack growth test is relatively stable, and the extensometer collects more test data, Through the processing and analysis of the data, more accurate conclusions can be obtained. Therefore, in the numerical simulation of the stress intensity factor at the crack tip, the relevant data with stress ratio r = 0.6 is selected for setting and analysis. Figure 1 shows the relationship between the crack length and the stress intensity factor at the crack tip in the numerical simulation and experiment when r = 0.6.
It can be seen from the figure that for the stress intensity factor at the crack tip under the condition of the same fatigue crack length, the development trend of the numerical simulation value is the same as that of the experimental value, which increases with the increase of the crack length. However, the stress intensity factor at the crack tip obtained by numerical simulation is always smaller than the experimental value. When the fatigue crack length is in the range of 9-25 mm, the two curves are basically parallel, and the difference is not big, and roughly meet the linear growth. With the increase of the fatigue crack length, the stress intensity factor curve of the crack tip obtained by numerical simulation continues to maintain a nearly linear growth, while the experimental value shows a nonlinear growth. With the growth of the crack length, the stress intensity factor value of the crack tip increases rapidly, and the distance between the two curves gradually increases.
It can be seen that the compact tensile specimen in the test is more sensitive to the change of crack length, and the crack length has a greater influence on the change gradient of stress-strain field at the crack tip, which leads to a larger change in the range of measured stress intensity factor at the crack tip, especially in the later stage of stable growth and rapid growth stage. This is because the steel plate in the actual rolling process does not rule out the inclusion, porosity and other processing defects. The numerical simulation is the ideal state of the experiment, and the material properties set are uniform, stable and isotropic. Therefore, the force of the model in the simulation process is uniform and stable, which is not affected by the processing defects of the material itself and the test equipment. It is more reliable and accurate to simulate the stable stage of fatigue crack growth of 42CrMo steel compact tensile specimen.