Assessing the Effect of Bend Twist Coupling on Impact Behaviour of Composite Hydrofoils

Abstract The application of hydrofoils reduces wetted area, drag and improves efficiency. To further improve hydrofoil efficiency, the effects of bend-twist coupling (BTC) through biased carbon fibre reinforced polymer (CFRP) laminate stacking sequence (LSS) can be investigated. These hydrofoil structures can be damaged in service. Therefore, the effect of LSS on damage resistance must also be considered. To investigate the effects of BTC, a representative hydrofoil was created, and its lift during operation calculated using Computational Fluid Dynamics (CFD). This pressure map was then exported to a Finite Element Model (FEM), where analysis could be performed on the hydrofoil, calculating deformation due to hydrodynamic loading and low-velocity impact (LVI). Furthermore, the effect of preload on impact response of each layup was investigated through the application of a 5 mm or 10 mm displacement at one end. A layup consisting of 30° plies, oriented according to the local bending moment showed a 23% increase in downwards twist under loading. A further revision using 0° plies at the leading edge reduced downwards twist by 6%. Impact simulations on each layup resulted in no change to damage, however peak contact force was seen to decrease as bias angle increased, with this trend stagnating at 30° bias, with a 16% decrease. Pre-load increased damage by 8% in the baseline layup. The results of this study showed that bend-twist coupling could improve the efficiency of hydrofoils, without decreasing resistance to damage under impact. Keywords bend-twist coupling (BTC); finite element analysis (FRE); impact behaviour; low velocity impact; hydrofoil