The Study Of Quantitative Estimate For Several Space Used Materials' Fatigue Crack Propagation

The fatigue at low stress is the most common failure form of the products. The uncommon failure of the single structure at the low stress will lead to a disastrous damage, especially in the products of the space ship etc, of which the structure and environment are complicated, the application of the new techniques and new materials are more. The research of the fatigue crack and the fatigue crack propagation rate are important for safe of the products.On the research of the propagation of the fatigue crack in the past 10 years, Paris and Zheng-hart have developed good formulas of the propagation of the fatigue crack of metal , but of which only describe the process of the propagation of the fatigue crack. There isn't a complete and quantificational formula to describe the whole process of the fatigue crack propagation.In the present thesis, researches on the moving rule of the drive and the resistance of the fatigue crack propagation is analyzed from micro-mechanisms and macro-mechanisms two aspects after reading a lot of propagation is gained by the method of combining the experiments and analysis in the quantificational parameter theory.On the research of the present thesis, we have read and analyzed the literatures in the past 10 years, analysis the parameter of drive and resistance of the fatigue crack propagation, provide the formulas of the fatigue crack propagation , and testify the formulas with the experiments of the related materials and the data provided by the literature.By the researching, we have developed the formulas of the fatigue crack and the wholeprocess of the fatigue crack propagation, gained that the whole fatigue crack propagation rate curve comprise the near-threshold region, the intermediate region of stable crack propagation and the rapid crack propagation region and with S shape, the crack propagation resistance is controlled mostly by the Yong's modulus, the crack propagation threshold and the fracture toughness. All the affects which affect the crack propagation rate is affected by this. The formulas of the crack propagation rate have important physical significance.