TWI has carried out a series of projects with Nabtesco Corporation in Japan on the design and optimisation of a composite part to replace one currently made of metal. The part, a reaction link, is a component in the flight control system of a commercial aeroplane and is used to adjust the flight attitude by moving the ailerons.
Reducing weight, increasing strength
Advanced composite materials such as carbon fibre-reinforced polymers can provide high specific properties and excellent fatigue performance compared to metals. These properties are very attractive to the aerospace industry, leading to an increasing demand for replacement of metallic parts with composites.
However, it can often be a challenge to design a composite component to meet the required structural performance with a significantly reduced weight. The type of fibre, stacking sequence, and geometrical dimensions of composite structures are commonly taken as design variables for tailoring and improving the structural performance of the product.
Optimisation of composite structures has become a key stage in the design of prototypes, and current finite element analysis (FEA) tools now make it possible to optimise complex composite structures.
Overcoming technical hurdles
The design for the reaction link was limited by severe spatial restrictions, and was also required to be suited to a simple, cost-effective manufacturing process. A two-dimensional gradient descent Newton-Raphson method was derived for implicit FEA-based optimisation of the composite lay-up, with the final design selected based on the relative proportions of 0 and 45 fibres in different areas of the part.