| Fatigue and fracture is caused by the failure of engineering structures and Components of the main reasons,Therefore, the Design of anti-fatigue in Engineering Structures, the selection of appropriate Counteracting fatigue design method is particularly important.Damage tolerance design is damage-safety design criteria and improvement.Damage tolerance design of components in the recognition of initial imperfections on the basis of there, through some testing technology to ensure before the next inspection to guarantee that the components have a certain residual strength and normal use. Thus, anti-fatigue with this method is applicable to the design. The damage tolerance design of the key problems is to correctly estimate the fatigue crack propagation life, Therefore, based on materials and structure elements for fatigue crack growth rate tests to determine the performance of its crack growth parameters, the correct estimation of crack propagation life is of decisive significance.This provides a solid theoretical basis in entire structure damage tolerance design.The main contents of this dissertation can be divided into three parts:the first part is study about fatigue crack growth rate test of the EH40 high-strength steel (ChapterⅢ); the second part is study about the relationship between fatigue crack growth rate and crack mouth opening displacement (ChapterⅣ); the third part is study about the fatigue crack propagation life of 14MnNbq steel (ChapterⅤ).Firstly, the fatigue crack growth rate of EH40 high strength steel was tested in accordance with British BS ISO-12108:2002 standard. The test results obtained the fatigue crack growth rate da/dN-ΔK curve and the associated performance parameters of crack propagation, which works for the estimation fatigue crack propagation life of EH40 high-strength steel used in Engineering Structure to provide a scientific basis. Meanwhile, the test results obtained fatigue crack growth rate curve for the 95.4% confidence the probability of dispersing bands of EH40 high-strength steel.Secondly, this paper study about the relationship between crack mouths opening displacement (CMOD) and the length of fatigue crack growth from the compliance samples and test the frequencies, The results show that both the relationship with the exponential growth function, through this relationship, for those who can not detect the case of components of crack length to provide a convenient way.Since to with the measured CMOD as a crack propagation control parameter, obtained with CMOD as the control parameters of fatigue crack growth rate expression:da/dN=D(CMOD)P,It not only describes the material phase of the expansion of linear elastic and plastic state when the material is extended, they can be used to describe the crack propagation, which also provides a new method of fatigue crack growth.Finally,using fracture mechanics method estimated the fatigue crackpropagation life of 14MnNbq steel.And from mathematical statistics methods provel4MnNbq steel distribution of fatigue crack propagation life is to follow the normal distribution, two requirements are given the reliability of any safe life under the method of crack propagation, at the same time, getting the fatigue crack propagation life probability density curve of 14MnNbq steel, which provides a help to analysis of overall life and remaining life of the structure for concerned professional designers.
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