Effect of potting support design on compression buckling of composite cylindrical shells

The design of thin-walled cylindrical shells under compression loading is mostly driven by buckling considerations. However, accurate experimental evaluation of the buckling load is challenging due to small variations in boundary conditions due to manufacturing tolerances in support conditions. To test a cylindrical shell under compression loading, potting support is usually created around its bottom circumference to avoid edge crippling that could otherwise drastically reduce its critical buckling load. Therefore, investigating the effects of the potting support on the buckling response of cylindrical shell structures is important to mimic boundary conditions as close as possible to real structural constraints of the boundary. The main objective of this work is to investigate the effects of single and double-sided potting supports on the critical linear buckling load of composite cylindrical shells under compression loading. Then, this paper provides insights into understanding underlying reasons for the deviations of theoretical buckling loads from their corresponding experimental values due to boundary conditions, which can occur independently from, or in combination with, geometric imperfection sensitivity. Finally, robust linear buckling expressions that can help designers estimate the reduction due to support conditions are presented. These expressions can be used for evaluating initial safety margins for the potting support design used for testing  cylindrical shells. </p

Bend-free design of super ellipsoids of revolution composite pressurised vessels

Bend-free design of super ellipsoids of revolution composite pressurised vessel

Bend-free design of super ellipsoids of revolution composite pressure vessels

Shells are thin-walled curved structures that are widely used in many engineering applications because of their structural performance in reacting transverse loads via generating membrane stresses. However, bending deformations and stresses are also generated, yet, alleviating them can result in more efficient use of material and improvement of load carrying capacity of shells. Ideally, a bend-free design provides scope for exploiting the full potential of load carrying in shell structures because of the uniform load distribution through the thickness. In this study, a family of so-called super ellipsoids of revolution are designed to have bend-free states under uniform internal pressure. Super ellipsoids of revolution have several advantages compared to conventional geometries such as higher packing efficiency, smoother stress flow variation, alleviating stress concentrations and cost associated with assembly processes. In this work, a new generalised set of governing equations representing bend-free states in composite super ellipsoids of revolutions are developed and solved analytically. Stiffness tailoring via tow steering is used to realise bend-free states. A parametric study is performed on several super ellipsoids of revolution for finding the required distribution of fibre orientations. The analytical solution is verified by finite element modelling and results are compared with an isotropic baseline

Bend-free design of ellipsoids of revolution using variable stiffness composites

Shells are commonly used in many structural applications due to their high specific load carrying capabilities. One of the most interesting features of shell structures is that they can resist external transverse loads by developing membrane stresses in the small deformation regime yet, in general, also generate inefficient bending deformations and stresses. In this study, a composite ellipsoid shell of revolution, under internal pressure, is designed for zero bending and curvature change. To this end, the stiffness properties of elliptical composite shell structures are tailored by fibre steering. A new definition for a bend-free state, independent of internal pressure, is presented. Based on this definition, the internal pressure-induced bending state of an isotropic ellipsoidal shell of revolution is compared with its tailored composite counterpart. Results show that up to a specific level of ellipticity, a bend-free state is achievable by fibre steering in elliptical composite shells of revolution. Finally, a failure study is performed to assess the potential improvement of the maximum allowable internal pressure by bend-free design

Static test of a thermoplastic composite wingbox under shear and bending moment

The proof of an aircraft’s structural integrity and safety is typically provided by analysis and supported by structural test evidence. The experimental test of a wingbox, which is the main structural component of a wing, can provide useful data on assessment of its structural performance in an actual airplane for the design objectives. To this end, a testing fixture was designed and manufactured to introduce a prescribed shear force and bending moment at one end of a variable stiffness thermoplastic composite wingbox and react the load at the other end. We report experimental results and compare them with detailed finite element data