疲劳寿命估算的能量法及其实验研究

根据疲劳损伤滞后能等效原理，导出了缺口件与光滑件的当量应力关系，通过Ｎｅｕｂｅｒ公式和饱和应力应变关系，可确定当量应力取值；采用定量方程随机化方程，建立了γ－ｐ－ε－Ｎ曲线（置信度－可靠度－应变－寿命曲线）公式及其实验测试方式；根据疲劳累积损伤理论和γ－ｐ－ε－Ｎ曲线公式，得到了随机载荷谱作用下构件疲劳寿命估算公式；最后，实验验证了复杂实测载荷谱作用下，ＬＹ１２ＣＺ铝合金含孔试样的疲劳寿命估算结果

THE ENERGY METHOD FOR FATIGUE LIFE PREDICTION AND EXPERIMENTRESEARCH

On the basis of the hysteresis energy conservation principle in fatiguedamage process, the equivalent stress of the notch specimen are derivedin this paper, taking account of the influence of initial crack length,cyclic behavior of materials, geometry of components and loading. WithNeuber equation and the steady stress-strain curve, this equivalentstress may be calculated. By the randomization method of deterministicequation, the γ-p-△εe-N curves (confidencelevel-probability of survival-strain-fatigue life curves),γ-p-△εp-N curve and their experimental determination methodhave been established, in which the scatter of materials and thenumber of specimens are taken into account. By means of the Mineraccumulation damage rule and γ-p-ε-N curves, the formulas topredict the safe life of components subjected to random load spectrumare presented and the predicted results accord with the fact thatfatigue life is scatter in practice. Therefore, the energy approach topredict fatigue life of components has been obtained. At last, thefatigue test of the notched specimens of LY12CZ under the actual loadspectrum is carried to validate the predicted results. From the testdata, we have that the mean of experimental life is 1594.75 blocks, themedian value of life is 1575.86 blocks on condition that logarithm offatigue life follows Gauss distribution, and the safe life with 99.9%probability of survival, 95% confidence level is 926.4 blocks. Usingthis energy method, the predicted median value of fatigue life is 1469.3blocks, and the predicted safe life with 99.9% probability of survival,95% confidence level is 879.6 blocks. From the calculated andexperimental results above, it is found that the predicted result issmaller than the experimental data, but their deviation is very small.So it is confirmed that the results estimated are safe and agree withthe experimental data.