Numerical simulation of fatigue propagation of mode I crack in compact tensile specimen of heavy load transmission gear

The model used for numerical simulation of fatigue crack growth is the same as the compact tensile specimen of 42CrMo steel shown in the above figure. Because the fatigue crack growth tests of the studied samples measure the fatigue crack length on the sample surface, the sample is uniformly stressed and the force is parallel to the sample plane. The model is simplified to plane stress state for effective analysis and decision.

In the actual experiment, the main parts include CT sample, pin, U-shaped collet and so on. However, in the process of numerical simulation of the test, only crack fracture is taken as the research object. The pin and U-shaped collet are not important components, so only the CT sample is modeled and studied in the numerical simulation. The specific modeling conditions are as follows: in the analysis process, the interaction between the pin and CT sample is not the analysis object, so the distributed coupling method is used to replace this part, that is, by setting two reference points, its position is the center of the loading hole. By setting the distributed coupling between the loading hole and the reference point, the synchronous displacement between them can be achieved. Then the load is directly loaded on the initial reference point to realize the relationship between the pin and CT sample in the experiment.

In the two-dimensional lapping plane problem, the limiting effect of U-shaped collet can be ignored. Therefore, it may not be taken into account here. The loading problem can be set by the method described above. The constraints of the specimen can be set by common boundary conditions. This method is efficient, accurate and reduces the workload of modeling. In the experiment, the U-shaped collet has two main functions: one is the limiting effect on the sample. However, since this study is aimed at the study of two-dimensional plane strain, its limiting effect on CT samples is ignored. Second, it plays a certain role in the loading process of the sample.

The fatigue crack propagation under the same experimental conditions is numerically simulated by ABAQUS software. The results show that the Mises equivalent stress nephogram at the crack tip in the numerical simulation state is consistent with the theory, and the stress is symmetrical with the horizontal line as the boundary. The closer to the crack tip, the faster the change, with an obvious gradient; Under the condition of the same crack length, the equivalent stress nephogram area of the smaller stress is larger than that of the crack tip. With the increase of the crack length, the area increases. Because the numerical simulation is carried out under ideal conditions, the test materials are uniform, stable and isotropic, and the load is applied smoothly, compared with the test results, the stress intensity factor at the crack tip under the same stress ratio and crack length obtained by numerical simulation is always small, and the calculated fatigue life is short, but the error is small, which is within the acceptable range, It can prove the reliability and accuracy of the numerical simulation method and the feasibility of the test, which lays a foundation for the bending fatigue test of gears in the next chapter.

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