Three-dimensional effects influencing failure in bend-free, variable stiffness composite pressure vessels

Pressure vessels enable liquids and gases to be stored and transported safely, finding pervasive use in many industries. These types of structure can be manufactured into many different shapes and from various materials to satisfy the requirements of their specific applications. Maximum allowable pressure is an important factor that should be considered carefully in the design process. Bend-free pressure vessels, that are enabled by variable stiffness composite designs, can even out in-plane stress distributions in the through-thickness direction thereby increasing overall load carrying capacity often accompanied by significant weight reduction. Bend-free composite vessels can therefore be considered to be possible candidates for the next generation of pressure vessels and therefore it is important to study their failure performance, often driven by safety reasons. In this study, the maximum allowable internal pressure is determined for bend-free ellipsoidal pressure vessels exploiting variable stiffness properties, using first-ply failure based on both Tsai-Wu and the recently proposed three-dimensional invariant-based failure criteria with performance subsequently compared against conventional constant stiffness, composite vessels. Parametric studies are then performed to provide physical insight and also to evaluate the effect of various material properties on the difference in failure load prediction found by these criteria.