Although the aerospace production process is much better controlled than the process in other industries, it remains true that very small manufacturing tolerances exist in the geometrical parameters (flange thicknesses, hole diameters, …) as well as in material properties. In the current design process, the effect of this manufacturing variability on the structural durability and safety 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 overdesigned
structures.
A much more promising approach is to include probabilistic models of design variables into the mechanical simulation process. Then, with a new methodology based on reliability analysis, engineers can obtain a better understanding of the actual effect of the manufacturing tolerances and of variability in material properties. Based on the analysis results, the robustness and reliability of the design can be assessed and improved if needed. In this paper, the above-mentioned probabilistic approach is demonstrated on two aerospace applications: a composite wing and a slat track structure. The material properties of the composite wing have been characterized with statistical distributions and their effect has been assessed on the static performance. For the slat track, measurements of different geometrical properties have been collected during the manufacturing process and their variability has been characterized probabilistically with statistical models.
Then, a reliability analysis has been carried out using morphing technology and fatigue life predictions with an industrial-sized FE model of the slat track to assess the reliability of the structure in terms of fatigue life. The outcome of the analyses consists of a probabilistic model of the structural performance (e.g. fatigue life for the slat track), given the variability in the geometrical and material parameters.
