| In the paper, some basic problem in the theory of fatigue damage are discussed with the method of microcosmic and macroscopically, and with uniting the fatigue damage microcosmic theory and macroscopically fatigue experimentation to analyze fatigue damage of the metallic material and to summarize the fatigue characteristic parameter, establish a new fatigue damage model. Simultaneity, the effects of temperature and cyclic loads about the fatigue damage for metallic component are discussed. A corroding to the theory forecasting the life spans and establishes the fatigue lifetime model for basic of the project application.Firstly, a corroding to the famous Miner theory, which analyze fatigue damage of the metallic component and establish the Miner model. But, in our practice, there is a difference between Miner model and fact. So, in the paper, analyze the damage relation between theory component and fact component by cycle loads, and define a new conception what damage effect is, establish a new model what is pyramid model, establish a new coefficient what is damage coefficient, Which approve that the difference exist between the real damage and theory damage in our paper, and supply a basic theory model for analysis the lifetime.Secondly, Analyze fatigue damage characteristic of the metallic welded joint according to the metallic fatigue damage result and welded joint characteristic. In the paper, this based on 16MnR alloy and through the experiment to take the mechanic parameter. Establish a new damage parameter, a new low cycle load fatigue damage life-span model of welded joint, and analyze the fatigue damage theory of the metallic welded joint by metallography.The last to analyze the metallic fatigue strength and fatigue damage lifetime, and establish the fatigue crack initiation equation, fatigue crack extend equation about the metallic welded joint, and analyze the new model application in the fatigue crack extend.
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