Crack growth evaluation on helicopter fuselage under spectrum loading

Damage Tolerance method for structural integrity evaluation of helicopters fuselages requests a detailed FE analysis validated through a dedicated experimental survey. This approach permits an important maintenance cost reduction and a structural safety improvement of helicopters frames. The construction of advanced FE models for the stress assessment can be used for the identification of the most critical area for crack nucleation and growth; the detection of these area permits a continuous monitoring of the damage with a sensors network (Comparative Vacuum Monitoring, Optical Fiber Sensors, Crack Propagation Gauges, etc). Therefore the final aim of the research is to obtain a reliable method to assess the damage accumulated in the fuselage by means of an advanced prognostic models that allow the real time definition of schedule for periodic and special inspections. Thus an increase in the safety of the aircraft by prognostic and monitoring of the frame is the main objective; in addition, the results achieved will be useful in the cost reductions regards maintenance operations and life extension for aged aircraft. According to this aim, a review of the state-of-the-art concerning the Structural Health Monitoring applied on helicopter fuselages will be first described in this paper. The review will be also focused on the numerical FE models of cracked structures and on residual life evaluation on helicopter fuselage. Moreover an example of FE models for the stress assessment and damage propagation an a real helicopter fuselage will be described in detail and the results compared with experimental relief with good agreement.