多轴疲劳寿命分析方法在飞机结构上的应用

针对飞机结构上常见的处于多轴应力应变(比例多轴)状态下的典型结构,采用3种多轴疲劳寿命分析模型,对该结构的疲劳危险部位进行疲劳寿命分析,并与单轴寿命分析方法的分析结果、疲劳试验结果进行了对比分析。首先对该结构进行细节有限元计算,确定结构的应力分布与应力水平,当载荷施加到88%的最大一级的峰值载荷时,疲劳危险部位的孔边即出现显著的塑性应变,因此,选用低周疲劳(LCF)寿命预测模型进行分析。选取的3种分析模型均是基于临界面的分析模型,分别是Wang-Shang模型、Smith-Watson-Topper(SWT)模型以及Morrow-Brown-Miller模型。为验证分析模型工程适用性,开展了该结构的多轴疲劳试验。与试验结果相比,3种分析模型的预测结果均偏大,其中Wang-Shang模型的预测结果最接近试验值,适用于本文这类结构;SWT模型和Morrow-Brown-Miller模型的预测结果误差相对较大。对于处于多轴载荷状态下的结构,应按照多轴疲劳寿命分析方法进行寿命预测,单轴疲劳寿命分析方法将给出过于危险的评定结果。

Application of multi-axial fatigue life estimation methods to aircraft structural components

The fatigue life of a typical aircraft structural component, which is subjected to a representative proportional multi-axial stress state, was evaluated using three different multi-axial fatigue life estimation models. Comparisons between the evaluation results obtained by multi-and uni-axial fatigue models and those with the test results were performed. Finite element analysis indicates that plasticity strain is significant on the fatigue critical details when the structure endurance reaches 88% of the peak load, therefore, low-cycle fatigue (LCF) life prediction models are reasonable. Three LCF models based on critical plane theory are selected to estimate the fatigue life of the structure, i.e., Wang-Shang's model, Smith-Watson-Topper(SWT)'s model and Morrow-Brown-Miller's model. Multi-axial fatigue test was also conducted to investigate the validity of the models for engineering application. The comparison results are as follows. The estimatied results of the three multiaxial models are all conservative, in which Wang-Shang's model gives a relatively smaller error and is acceptable for such structures. The errors of SWT's model and Morrow-Brown-Miller's model are much greater. For the fatigue assessment of such structural components subjected to multi-axial loading, multi-axial fatigue life estimation methods must be used since the uni-axial fatigue life method will give too dangerous estimation.