Effect of Flight Spectrum Loads on the Damage Tolerance Evaluation of a Helicopter Frame

The Damage Tolerance method for structural integrity evaluation of helicopters fuselages requests a detailed FE (Finite Element) 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 and the detection of these areas permits a continuous monitoring of the damage with a sensor network: assessing the damage accumulated in the fuselage by means of advanced prognostic models that allow the real time definition of schedule for periodic and special inspections. The results achieved are also useful in the cost reduction regarding maintenance operations and life extension for aged aircraft. According to this aim, a review of the state-of-the-art concerning Structural Health Monitoring (SHM) applied to helicopter fuselages is first described in this chapter. The review also focuses on the numerical FE models of cracked structures and on the residual life evaluation on helicopter fuselages. Moreover, an example of a FE model for the stress assessment and damage propagation of a real helicopter fuselage is described in detail and the results compared with experimental relief with good agreement.