Titting Confirmation And Analysis Of New Fatigue Crack Propagation Model

The study of fatigue crack growth is of great importance in engineering. The application of various models such as rain-flow method or square root method is all trying to use an alternative load instead of the actual load. but because its basic theory is based on empirical formula, the effect can not be close to the truth.Xu Zhong-yong proposed a new theory of fatigue crack growth considering the inertia effect from the last century 90's, and then inferred fatigue crack growth equations under symmetry and asymmetry constant amplitude loading and random spectrum loading. On the basis of previous research, this paper extended the optimal constant amplitude fatigue crack growth equation of non-symmetrical load to range of amplitude loading conditions. By fitting the experimental data of foreign research content, results are as follows:(1) The proposal of the Inertia effect coefficient m makes that the study of fatigue crack growth theory can be consistent with the basic laws of newtonian mechanics and the concept of fracture mechanics. This paper extended the equation of fatigue crack growth under the constant amplitude load to the mutative and random spectrum loading. It is not necessary to study the details of every cycle propagation, we just equivalent the propagation to the propagation of constant amplitude loading with the mathematical basis of Integral mean value theorem. It is proposed that we can repace the expression of structure of crack tip stress intensity factor as the expression of infinite plate with the reason of Crack tip singularity.(2) This paper uses a non-symmetrical load of constant amplitude fatigue crack growth equation to fit the experimental data of mutative amplitude spectrum fatigue crack propagation. We found that the theoretical data obtained from the fitting is consistent with the experimental's.(3) The Npred/Ntes obtained from our study is between 1.00 and 1.10 seeing from the results of predition life. But the Npred/Ntes obtained from"Improved Methods For Predicting Spectrum Loading Effects-Phase I Report"is between 0.15 and 2.07. Compared with the two, the data from the method of this paper is closer to the real situation.(4) This paper finds that c = m ?σa is a quantity and a constant in the fitting process, which means that we can use a equation under symmetry constant amplitude loading to replace what under random spectrum loading without increasing parameter.The paper also suggests further prospects on the following studies of this series of research.