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在介绍了有限寿命设计的二个依据:动载荷分析和材料及构件的抗力指标之后,从本讲开始介绍有限寿命设计的第三个依据:有限寿命设计的理论和方法。限于篇幅,本讲座着重介绍疲劳累积损伤理论,并从应力与寿命的关系、应变和寿命的关系及裂纹扩展速率与应力强度因子之间关系三个方面介绍估算寿命的方法和步骤。本讲将介绍三个问题:疲劳破坏的机理、损伤度及其衡量指标及累积损伤的几种理论。一、疲劳损伤机理疲劳破坏与静力作用下的失效有本质的区别。尽管机械零部件的几何形状和受力方式千差万别,它们的载荷变形曲线也各不相同,但是在静载作用下的破坏过程一般地都要经历弹性
After introducing the two basis of finite-life design: dynamic load analysis and the resistance index of materials and components, the third basis of finite-life design is introduced from this lecture: theory and methods of finite-life design. Due to space limitations, this lecture focuses on the cumulative fatigue damage theory, and describes the methods and steps for estimating life from three aspects: the relationship between stress and life, the relationship between strain and life, and the relationship between crack growth rate and stress intensity factor. This lecture will introduce three issues: the mechanism of fatigue failure, the degree of damage and its measurement indicators, and several theories of cumulative damage. First, the fatigue damage mechanism Fatigue damage and failure under static effects are essentially different. Although the mechanical parts and the way they are subjected to stress vary greatly, their load-deformation curves are also different, but the destruction process under static load generally undergoes elasticity.