Improving reliability of a composite wing structure (Miglioramento dell’affidabilità di un’ala in composito)

Knowing the inherent risk of failure in any design is becoming increasingly important to both the manufacturer and the customer. Unfortunately current aerospace design analysis methods do not directly account for the random nature of most input parameters. This is particularly true for composites. Inherent variabilities in the manufacturing and assembling processes are not always known or characterized. It is however clear that new aircraft developments (e.g. reusable launch vehicles, high-speed civil transports) can only be successful if consistent changes in the traditional design procedures are made. In the current design process, the effect of these variabilities on the structural performance cannot be accurately assessed and is hence compensated for by applying safety factors. This is not an ideal situation, as it may lead to slightly over-designed structures. In order to integrate the simulation environment and the production variability, a much more promising approach has been worked out that includes probabilistic models of design variables into the mechanical simulation process. In this way, real variability of design parameters can be taken into proper account in the simulation environment and then used to assess structural reliability. It is, in fact, vital to better understand how scatter in physical properties affects the behavior of a composite structure, and to assess which physical properties are most critical. When accurate stochastic descriptions of physical properties are available, these can be integrated into the design process of composite structures, and a control and optimization tool can be developed to avoid unnecessary weight increase, to reduce allowable knockdown factors and to correctly re-define inspection intervals.