综合考虑载荷谱和结构特性分散的概率断裂力学方法

在飞机结构的设计定型阶段,要综合考虑载荷谱和结构特性的分散评估机群的可靠寿命。为此,进行了某型飞机结构细节的TA15M钛合金模拟试件在3个单机谱下的耐久性试验,断口判读得到主裂纹扩展(a,t)数据,反推得到了当量初始缺陷尺寸(EIFS)。对比分析表明,载荷谱分散对EIFS分布参数无影响,估计得到了通用EIFS分布参数。建立了考虑载荷谱分散的裂纹扩展对数正态随机变量模型及参数估计方法,由此确定裂纹超越概率并进行损伤度评估,建立了综合考虑载荷谱和结构特性分散的概率断裂力学方法(PFMA)。

Probabilistic fracture mechanics approach accounting for both the variability of load spectra and of structural properties

In the design phase of aircraft structures, the fleet reliability should be evaluated accounting for both the variability of load spectra and of structural properties. For reliability life evaluation, a durability test under three individual load spectra is conducted for the specimens of TA15M titanium alloys stimulating the aircraft structure details. The lead crack growth (a,t) data are obtained. As a result, the equivalent initial flaw size (EIFS) values are back-extrapolated. Statistical analysis demonstrates that the variability of load spectra has no obvious influence on the EIFS distribution. The general EIFS distribution parameters are subsequently estimated. A log-normal random variable model is derived analytically to describe the crack growth rule accounting for the variability of load spectra and pertinent parameter estimation method is given, upon which the probability of crack exceedance is derived and the extent of damage is evaluated. Consequently, a probabilistic fracture mechanics approach (PFMA) is developed accounting for both the variability of load spectra and of structural properties.