裂纹形成寿命的类比估算法

 本文提出一种零部件的裂纹形成寿命的类比估算方法。即用已知零部件在谱载荷作用下,经过耐久性试验所得到的寿命（或使用寿命）来类比估算其它未经过耐久性试验的同类型的零部件的寿命。本文通过推导给出具体类比估算公式,它基本上可以消除Miner公式中常值Q的分散的影响,从而可以提高寿命估算的准确性。本文还给出了在五种谱载荷作用下的试样的类比估算和飞机的大型结构件的类比估算实例,并得到疲劳试验的验证。 在1979年类比计算寿命的研究工作中,曾得到北京航空学院高镇同教授的指导和空军研究所侯同英工程师的算例的验证。在试样类比计算中,北京材料研究所顾明达、张诗捷工程师无私地提供了试验数据。在此表示感谢。

AN ANALOGY METHOD FOR CRACK INITIATION LIFE PREDICTION

A method for crack initiation life prediction of components is presented. This method employs the life of a given component obtained from endurance tests under spectrum load to predict the life of another untested same type component by analogy.The formula for analogy life prediction is deduced from Miner's theory and formula SmN=C as follows:or where ni,, Sai, Δgi and λ are load cyclic number, stress amplitude, overload increment and life cyclic number of the given component in i level; ni', S'ai, Δgi' and λ' are those of the unknown component; Sap and Δgp are any constant stress amplitude and overload increment （they may be taken as unit in calculation）; m1, m'i are constant （generally between 5 and 10） and may be estimated from the S-N curve or by experiments. In life prediction with this formula it is unnecessary to choose the constant Q in Miner's formula, therefore its accuracy may be improved.The lives of large components of two aeroplanes and the specimens under five different loading conditions are predicted by this analogy method. The results are quite consistent with fatigue test results and the comparison is shown in tables （ 4 ） and （ 3 ）. This demonstrates that the formula presented in this paper is more accurate, particularly for components analogous to given ones, and may give quite satisfactory results provided the value of the m is estimated appropriately. According to Miner's theory it is possible to apply this analogy method to components different from given ones, but it is necessary to make appropriate correction in actual use.