Failure performance of bend-free variable stiffness composite pressure vessels

Pressure vessels are designed to store liquids and gases and have various applications spanning from chemical plants to automotive and aerospace industries. Currently, lightweight composite pressure vessels are desirable, especially in transportation industry applications because of their subsequent benefits in fuel consumption, cost and environmental issues. Using composite materials for pressure vessels along with advanced manufacturing technologies such as automated fiber placement provides excellent scope to tailor stiffness through the structural surface using fiber steering to achieve desirable structural performance. Recently, variable angle tow (VAT) technology has been used to suppress bending in super ellipsoids of revolution composite pressure vessels, resulting in minimizing the inefficient bending stresses and deformations and increasing their load-carrying capacity. It is worth noting that such geometries can provide excellent packing efficiency. These advantages make the bend-free super ellipsoids of revolution composite pressure vessels potential candidates for the next generation of pressure vessels. Therefore, their failure performance as the most important design factor should be studied carefully due to safety reasons. In this study, the maximum allowable internal pressure for VAT bend-free ellipsoidal pressure vessels, using the first-ply failure based on both Tsai-Wu and three-dimensional invariant-based failure criteria is determined. Subsequently, VAT bend-free pressure vessels’ failure performance is compared against that obtained for conventional constant stiffness composite vessels. Among structures considered, the VAT bend-free composite vessel has the best failure performance. Moreover, the predicted failure load using the three-dimensional invariant-based failure criterion for the VAT bend-free design is 34% lower than the failure load predicted by the Tsai-Wu. Finally, the effect of various material properties on the difference in predicted failure load using these criteria is assessed. Results provide physical insight useful for designers in materials selection.