考虑多轴应力与共振影响的随机振动疲劳寿命预测

目前工程上计算结构随机疲劳寿命时,仍经常采用基于单轴拉-压疲劳寿命(Stress-Number of cycles,S-N)曲线的应力寿命方法。虽然使用简单方便,但这种方法不仅忽视了单轴S-N曲线且不能准确反映结构在多轴应力状态下的疲劳,还忽略了随机振动中共振对结构疲劳寿命的影响,因此该方法在预测结构在随机振动下的疲劳寿命时与实际寿命往往有较大误差。对此引入三轴因子来反映结构在随机振动下的多轴应力状态,同时推广得到其在频域上的表达式,并在此基础上引入非线性函数,提出了一个新的随机振动疲劳损伤参量——多轴振动因子。新的损伤参量不仅同时考虑了结构随机振动下的多轴应力状态与共振对疲劳寿命的影响,而且该损伤参量形式简单,便于工程应用。利用新的随机振动疲劳损伤参量,得到了适用于随机振动下的多轴S-N曲线,从而建立了一种新的随机振动疲劳寿命预测方法。通过对7075-T6和LY12CZ铝合金缺口试件的随机振动疲劳寿命进行预测,结果表明该方法较准确地预测了两种缺口试件随机振动下的疲劳寿命。

Random vibration fatigue life prediction considering the effects of multi-axial stress and resonance

In calculating random fatigue life of structures in engineering at present, the stress life method based on the axial tension-compression fatigue life S-N(stress-number of cycles) curve is often used. Easy as it is to use, it often ignores not only the single-axis S-N curve, causing inaccurate reflection of the effect of multi-axial stress state, but also the resonance on the structure fatigue life in random vibration, as a result, the method in the prediction of fatigue life of structures under random vibration with actual life tends to have a larger error. The triaxial factor was introduced to reflect the multi-axial stress state of the structure under random vibration, and its expression in frequency domain was generalized. Based on this, the multi-axial vibration factor, a new random vibration fatigue damage parameter, was proposed. The new damage parameter not only considers the effect of multi-axial stress state and resonance on fatigue life under random vibration of the structure, but also has a simple form for engineering application. By using the new random vibration fatigue damage parameters, the multi-axis S-N curve for random vibration was obtained, and a new random vibration fatigue life prediction method was established. By predicting the random vibration fatigue life of 7075-T6 and LY12CZ aluminum alloy notch specimen, the results show that the method can accurately predict the fatigue life of two kinds of notch specimens under random vibration.