基于疲劳短裂纹行为的疲劳寿命估算方法

摘要

The process of forming short fatigue crack was di vided into short fatigue crack initiation phase and short fatigue crack propagat ion phase. The theory of continuously distributed dislocations of crack was app l ied to analyze the early growth and the effect of microstructure of short fatigu e crack. The dislocations model of crack under cyclic stress was built based on the analysis of the equilibrium condition for dislocations when the applied stre ss was reduced. The reverse plastic displacement at the crack-tip was adjusted to discribe the growth of fatigue crack. The model was used in short fatigue cr a ck initiation with the physical background of the diceleration behavior of early growth of short fatigue crack. A fatigue limit diagram of hyperbola was derive d from the threshold stress condition of short fatiuge crack determined by the an alysis of interactions between early growth of short fatigue crack and grain bou ndary. The equation of short fatiuge crack growth rate was presented from the m o del related to the threshold stress condition of short fatigue crack. The ellip s oidal inhomogeneity method was applied to the study on elastic-plastic fractrue problem, and then the analytical expressions of crack-tip extension displaceme nt were found. The method in which crack-tip extension displacement range was u tilized to describe the rate of short fatigue crack propagation was presented. I t was found that the propagation rate of short fatigue cracks. Based on the beh a vior of initiation and propagation of short fatigue cracks, a method of predicti ong fatiuge life was proposed. The predicting result shows that this method was accurate enough.%在疲劳短裂纹形成和扩展行为研究基础上，提出了一种疲劳 寿命估算方法。计算结果表明，该方法具有满意的预测精度。