Analysis Of Stress Intensity Factor And Fatigue Crack Growth Based On XFEM

So far, there are many mature methods to study the fatigue crack propagation of three-dimensional inclined cracks in China and abroad, this paper mainly introduces the basic theory of extended finite element method and its improvement, at the same time, summarize the basic theory of fatigue crack growth, make a numerical analysis on the three-dimensional oblique crack and the first order transmission helical gear in the ABAQUS software, deeply studied the variation of the three-dimensional oblique crack propagation path and the influence factors of the stress intensity factor. The main research work and results are as follows:1. On the basis of the basic theory of the extended finite element method, an improved scheme of XFEM is proposed for the change of 3D crack propagation. In the modification scheme, the method of default virtual crack is used to determine the crack tip element, Under the action of external load, when the crack is in the process of expanding, the crack will begin to expand as long as the crack tip stress reaches the crack criterion, in the process of crack propagation, the physical and geometrical properties of the crack tip are changed. In order to accurately track the crack propagation, the level set of each unit node is needed to be updated, one of the most convenient method is to update the local area.2. Corresponding stress intensity factors are solved by different methods, at the same time, compare the advantages and disadvantages of several methods, finally,improve XFEM is the best method to solve the stress intensity factor of three-dimensional inclined crack. At the same time, the influence of the inclined angle on the stress intensity factor is analyzed.3. The stress and strain diagram of the crack propagation path with the change of the load step is obtained by the simulation of the 45 degree eccentric crack extending in a rectangular plate. In the process of crack propagation, the stress distribution of the model is affected by the existence of the crack, the crack tip is in the state of stress concentration, stress value at the crack tip is the largest, and is gradually reduced at the far away from the crack tip. The crack surface is free, so the stress value is the lowest. The results obtained in this paper meet the theoretical requirements, which are compared with the results in the literature as well as the results of the theory.4. Three dimensional crack propagation path and crack initiation angle of theeccentric distance. We can be observed that the eccentric diagonal crack propagation path is extended along the left and right. In the process of propagation, the crack is extended along the straight line, when the oblique crack is not eccentric, the crack tip is the same around the crack tip, along with the inclined crack to the left, the crack of the crack is gradually reduced, and the left crack angle is larger than the right crack angle, these conclusions are consistent with the maximum circumferential stress theory.5. Expansion simulation of the first stage transmission helical gear. The conclusion is that crack angle will influence helical gear root crack expansion path at the crack tip, the equivalent stress distribution and helical gear equivalent crack tip displacement.