The Research Of Crack Growth Life For MSD On Fuselage Panel

Widespread Fatigue Damage(WFD) is a kind of structure fatigue damage revealed in Aloha accident, which is a main threat to airplane safety. Multiple site damage(MSD) is a main reason causing WFD in airplane structure. The research about the being of MSD and fatigue prosperity of MSD crack has been received more and more concern. Civil aircraft fuselage longitudinal skin lap is typical structure that is susceptible to MSD,the research of MSD crack propagation life in vertical bearing porous structure is the foundation of WFD sensitive structure evaluation.Aiming at the problem of MSD crack propagation problem in skin panels, the combination method of calculating crack tip stress intensity factor and the mutual influence between cracks is the core. Based on the research of the rule of the combination method of calculating crack tip stress intensity factor, a stress intensity factor database was established. The program of calculating the propagation life of MSD cracks in fuselage panel was established on the base of the combination of the database, Paris formula and the failure principle of MSD panel.The fatigue life of porous panel was calculated by combining the probability method of simulating crack initiation and deterministic method of crack propagation. MSD crack propagation characteristics analysis was made according to the result of fatigue life of a single MSD model, and the failure probability and the average behavior of WFD under given loading conditions was determined by Monte-Carlo simulation method. According to Monte-Carlo simulation results, the analysis of the correlation between initiation life and propagation life of MSD panel was made in the paper.Airworthiness requirements of WFD assessment was elaborated, and the method of determining the inspection start point and modification point basing on result of assessment was discussed. Finally a method of determining the monitoring phase corresponding to confidence level was put forward, and the determination method for the variable monitoring stage are described.This paper aims to provide a reliable calculation method of fatigue life of porous panel structure and compliance method of determining the time period for the inspection and monitoring of MSD.