Tolerance management during the design of composite structures considering variations in design parameters

Composite structures play an important role in realising resource-efficient products. Their high lightweight potential and improved manufacturing technologies lead to an increased use in high-volume products. However, especially during the design and development of high-volume products, the consideration of uncertainties is essential to guarantee the final product quality. In this context, the use of modern lightweight materials, such as fibre reinforced plastics (FRP), leads to new challenges. This is due to their high number of design parameters, which are subject to deviations from their nominal values. Deviating parameters, e.g. ply angles and thicknesses, influence the manufacturing process as well as the structural behaviour of a composite part. To consider the deviating design parameters during the design process, a new tolerance optimisation approach is presented, defining tolerance values for laminate design parameters, while ensuring the functionality of the composite structure. To reduce the computational effort, metamodels are used during this optimisation to replace finite element simulations. The proposed approach is applied to a use case with different key functions to show its applicability and benefits.

Residual Strength Optimisation of a Vent Hole in an Aircraft Component Using a Heuristic Method

The paper presents application of damage tolerance optimisation principles to the design of industrial components. It is illustrated via design optimisation of a Fuel Flow Vent Hole (FFVH) located in the Wing Pivot Fitting (WPF) of an F-111 aircraft. The aim is to determine the shape of the cutout that will maximise its residual strength under the operating loading conditions. Damage tolerance shape optimisation is performed using a heuristic optimisation method known as the ‘Biological algorithm’. The maximum stress intensity factor (SIF) for all of the cracks around the boundary of the optimal cutout is found to be significantly lower compared to that of the initial shape. This shows that an improved residual (fracture) strength is achieved for the optimal designs. The variability in SIF around the cutout boundary is reduced, thereby making the shape more evenly fracture critical. The shapes of the residual strength optimal vent holes are found to depend on the initial crack sizes. It is also shown that a damage tolerance optimisation additionally produces a lighter WPF component design, which is highly desirable for aerospace industries.