基于断裂力学方法的粉末盘低周疲劳寿命预测

Fracture Mechanics Method Based LCF Life Prediction for Powder Metallurgy Disks

为克服传统寿命预测未能考虑粉末合金夹杂物的缺陷,在某粉末封严盘定寿过程中,使用计算断裂力学方法模拟了夹杂缺陷从初始状态一直增大到可检尺度的扩展过程,并将该过程经历的循环数作为裂纹萌生寿命。在考虑小裂纹扩展速率修正的情况下萌生寿命为1639循环,若不采用修正则为4956循环,说明忽略"小裂纹效应"会得出偏于危险的萌生寿命计算结果。对含裂纹有限元模型的建立、裂纹扩展寿命计算中积分路径的选取等问题进行了讨论。使用断裂力学方法预测裂纹萌生寿命需要重复多次有限元计算及前沿光顺化处理,时间耗费较大,但在精确定量分析方面具有优势,可作为现有方法的有益补充,为发动机限寿件检修周期的确定提供依据。

The traditional life prediction methods lack the consideration for inclusion influence in powder metal-lurgy （ PM） . To overcome this shortcoming, the computational fracture mechanics is used to simulate the propaga-tion process, which ranges from initial size to detectable size, of an inclusion-induced defect in a PM labyrinth seal disk. The number of cycles corresponding to the propagation process is considered as the crack initiation life. The initiation life of the crack originating from the initial inclusion is 1639 cycles when using the modification model of crack growth rate for small cracks, and the result is 4956 cycles if the modification model is not adopted. It indi-cates that ignoring the “small crack effect” can lead to a dangerous estimate of crack initiation life. Furthermore, the establishment of crack-embedded finite element models and the chosen of integration path for crack propagation life estimation are also discussed. Fracture mechanics based crack propagation life prediction needs many repeated finite element calculations and smoothing treatments for crack fronts, so it is time consuming and labor intensive. However, its advantage in precise and quantitative analysis makes it a favorable supplement to current methods and it is helpful when determining the time between overhauls for life-limited parts.