谱载下密封角盒螺栓及长桁端头疲劳寿命估算的逐次累计求和算法

CYCLE-BY-CYCLE ACCUMULATION ALGORITHM FOR PREDICTING FATIGUE LIVES OF BOX-CORNER BOLT AND STRINGER JOINT UNDER SPECTRUM LOADING

对在谱载疲劳试验中发生断裂失效的中机身密封角盒连接螺栓和中央翼上壁板长桁端头进行了断口扫描电镜(SEM)分析,研究了谱载下两类连接件的破坏模式和机理,并利用断口定量反推技术,判读了中机身密封角盒连接螺栓和中央翼上壁板长桁端头的裂纹扩展寿命;然后,根据名义应力法,建立了复杂连接结构的疲劳性能S-N-KTE(疲劳应力-疲劳寿命-应力集中系数)曲面模型;利用该曲面模型及断裂力学理论,发展了用来估算谱载条件下复杂连接结构疲劳寿命与裂纹扩展寿命的逐次累计求和算法;最后,运用该文提出的寿命估算方法,估算了谱载下中机身密封角盒连接螺栓及中央翼上壁板长桁端头的疲劳寿命与裂纹扩展寿命,估算结果与断口判读结果吻合良好。

Fatigue tests are respectively carried out on box-corner bolts and stringer joints under spectrum loading,failure modes and mechanisms are investigated through SEM analysis,and fatigue crack growth lifetimes are determined from fractographic-quantitatively-interpreted data by using the reverse inference method.From the nominal stress method,a fatigue S-N-KTE(stress-life-stress concentration factor)surface model is developed to characterize the fatigue characteristic of complex jointed structures,and the cycle-by-cycle accumulation algorithm is developed for predicting the fatigue lifetimes and crack growth lifetimes of jointed structures subjected to random spectrum loading.Finally,a new model and an algorithm are used to predict the fatigue lives of box-corner bolts and stringer joints under spectrum loading,demonstrating good agreements between the predictions and experiments.