Factors affecting the calculation of fatigue crack length in three－point bending specimens using the flexibility method

The flexibility method was used to calculate the fatigue crack length of three－point bending specimens with different thicknesses. Combined with the finite element simulation analysis method, the influence of factors such as specimen thickness, applicable conditions of the flexibility function relationship, material elastic modulus, crack front edge bending degree and extensometer gauge length on the accuracy of the flexibility method in calculating crack length was studied. The results show that a normalized actual crack length of no less than 0.3 was a necessary condition to ensure the accuracy of the flexibility method calculation results. When using the finite element method to simulate a straight through type crack and normalizing the simulated crack length to be no less than 0.3, the compliance function relationship had a high degree of agreement with the simulation results. When the thickness of the specimen was not greater than 40 mm, using the elastic modulus of the material in the flexibility function relationship could obtain a more accurate calculation result. As the thickness of the specimen increased, the angle of the crack leading edge arc increased, and the crack flatness decreased, resulting in the calculated crack length being smaller than the actual crack length.