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利用门槛值以上的疲劳裂纹扩展率和裂纹开口位移之间的正比例关系表明:在相当大范围内,不同材料的疲劳裂纹扩展量可以精确地用材料本身和两个材料常数,即比例常数A和应力强度因子门槛值Kth来加以说明。在R≈0时,用计算机对大约65组试验数据进行分析的结果表明:本方法在裂纹扩展速率相当于约10~(-4)时/周时是有效的,即直到由韧窝组织引起的裂纹传播开始时是有效的。可以发现:在无侵蚀环境下,A与裂纹扩展的屈服应变有关,而且它随环境之恶劣程度的增大而增大,相反,Kth随之减小。这种变化提供了测定环境恶劣程度的方法。在无侵蚀环境下,裂纹扩展与屈服应力无关,而对门槛值之上的应变强度因子成正比。把A值和Kth值作为材料性质,环境情况及加载条件的函数列成表格,即可计算疲劳裂纹扩展速率和确定有缺陷的构件之残余寿命的系统的工程方法。
The proportional relationship between the fatigue crack growth rate above the threshold and the crack opening displacement shows that within a fairly large range, the fatigue crack growth of different materials can be accurately defined by the material itself and the two material constants A and Stress intensity factor threshold Kth to illustrate. A computer analysis of about 65 sets of experimental data at R≈0 shows that this method is effective at a crack growth rate equivalent to about 10 -4 / wk, ie until caused by dimples Crack propagation is effective at the beginning. It can be found that in the non-erosion environment, A is related to the yield strain of crack growth and it increases with the worsening of the environment. On the contrary, Kth decreases. This change provides a measure of how bad the environment is. In a non-corrosive environment, crack propagation has nothing to do with yield stress, but is proportional to the strain strength factor above the threshold value. A systematic engineering approach to calculate the fatigue crack growth rate and to determine the residual life of a defective component by tabulating the values of A and Kth as a function of material properties, environmental conditions and loading conditions.