Abstract
The behaviour of fibre-reinforced composites greatly depends on their layup structures. Through a full-field layup optimization study based on multiple parameters, this paper investigates how different properties change with the layup. The aim was to maximize the extension-twist coupling performance while ensuring adequate bending stiffness and low thermal warpage to make the laminate suitable for shape-adaptive helicopter rotor blade application. The Classical Laminate Theory-based calculations revealed that satisfying the bending compliance and thermal warpage criteria significantly limited the achievable extension-twist performance. The warpage limit affected the desired coupling behaviour more because both properties are driven by terms in the extensional-bending compliance matrix, unlike bending compliance. Symmetric laminates do not have an intrinsic extension-twist capability, but some asymmetric laminates demonstrated significant coupling performance while being practically warpage-free (based on the ISO2768 standard). The results prove that the advantages of asymmetric laminates can outweigh their sometimes negligible disadvantages. The paper also investigates if there is a universal tendency in how layup homogenization affects the terms of the bending compliance matrix of composites. Through analytical calculations, we showed that depending on the layup of the sub-laminate, homogenization can increase or reduce the value of any term in the bending compliance matrix; therefore, there is no universal tendency. Based on these results, layup homogenization cannot only be exploited for its most general purpose – warpage mitigation – but also for improving other characteristics of the laminate (e.g. reducing the bending compliance for increased bending stiffness or increasing the bend-twist compliance for improved coupling performance).
Highlights
Composites – especially fibre reinforced ones – are mainly used in the industry due to the excellent strength and stiffness they can provide while being lightweight
3.1 Multi-parameter layup optimization As an example, the goal of the optimization study is to maximize the extension-twist performance of a 4-ply laminate so that it can provide an aerodynamic advantage when used as the material of a shape-adaptive helicopter rotor blade
As the [b] matrix values are zero in the case of symmetric laminates, those laminates are in the origin of the graph, and all the other markers in Fig. 3 represent asymmetric laminates that traditionally would not be used in the industry due to their thermal warpage
Summary
Composites – especially fibre reinforced ones – are mainly used in the industry due to the excellent strength and stiffness they can provide while being lightweight. The value of composites can be further increased by improving other properties of the material, too. Many research projects have focused on increasing the ductility of composites to mitigate one of the most significant disadvantages of these materials: brittle failure. Besides improving certain properties of composites (e.g. ductility [4, 5], impact resistance [6, 7] or fire retardancy [8, 9]), they can be endowed with additional functionalities that can increase their advantage over competing structural materials. Coupling refers to a direct connection between loads and deformations of
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