Nonlinear buckling of delaminated panels

• Main Author: Vollmecke, Christina
• Other Authors: Louca, Luke
• Published: Imperial College London 2010
• Subjects: 629.13
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517685

Laminated structures have increasingly gained popularity in engineering applications owing to their advantageous properties. Particularly in aerospace applications, laminated components, typically comprising fibre-reinforced composites, have a soaring demand owing to their high strength to weight ratio. However, owing to the complex nature of the material, several different failure mechanisms may occur; amongst them is delamination, i.e. the separation at the interface between two laminates. This defect is often difficult to detect, yet may significantly reduce a component's load carrying capacity and subsequently may severely affect its safe working conditions. It is therefore of utmost importance to assess the effects of delaminations on the structural elements carefully. Since components in aerospace applications often comprise laminated panels, a geometrically nonlinear plate delamination model is derived analytically by extending a previously developed two-layer strut model. This type of structural component is commonly analysed as an engineering simplification since at plates are often used as an archetype to simplify more complex structural forms. Thus, an isotropic plate is currently considered, which re ects the simplest constitutive behaviour, and it can represent to some extent the behaviour of a laminated composite that has a uniform or symmetric lay-up sequence. A rectangular defect is located in the centre of this uniformly compressed, isotropic rectangular plated panel representing the delamination. Whilst trigonometric out-of-plane displacement functions are used in a Rayleigh{Ritz procedure yielding the governing equations that describe the mechanical behaviour of the plate, in-plane deformations are obtained via von Karman's compatibility equation. An indication of the residual capacity of the panel after critical buckling is obtained by investigating the nonlinear postbuckling range, where delamination propagation is incorporated by introducing a discrete cohesive zone model at the boundaries of the delaminated region. Different configurations are investigated in the neighbourhood of the previously evaluated transitional depth of delamination, which constitutes the boundary between local and global buckling. Initially, a uniformly spreading defect is investigated for various different defect sizes and depths. Subsequently, geometric parameters are linked to the response of the panel to generalize the outcomes with quantitative comparisons being undertaken against previous results and those obtained with the commercial nite element software ABAQUS. It is found that the model compares well and several criteria for the initial design of the damaged panels are proposed such that delamination growth may be accommodated safely and e ciently. Furthermore, uni-directional growth of the delamination is considered in a pilot study with suggestions being made regarding the growth direction tendency.