Optimized fiber steering and layer stacking for elastically tailored, damage tolerant laminates

A combined minimum-mass optimization strategy for Variable Angle Tow (VAT) panels subject to buckling and damage tolerance constraints is presented. The manufacturing process of Continuous Tow Shearing (CTS) is employed to form the laminates which have variable thickness due to tow shear deformation of dry tows. The panels under compression load are modeled using an infinite strip method to predict the panel buckling load and an efficient damage tolerance model is applied to obtain the threshold strains for crack propagation at delamination interfaces. Straight fiber ±45° plies show a good compromise between damage tolerance and buckling capacity by a trade-off study. These plies are added to the surfaces of the optimum buckling design to improve the Damage Tolerant (DT) strength in the highly-stressed area near the panel boundaries. This buckling/DT laminate is re-optimized with buckling and damage tolerance constraints. The results show that the damage tolerant strength of buckling/DT laminate improves by up to 71% with 6% weight saving compared with the laminate optimized with only buckling constraints. Hence, the proposed optimization strategy provides structurally efficient solutions for optimum design of CTS panels with buckling and damage tolerance constraints.