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In this article, the effects of damage (delamination) on the structural vibration characteristics of spar wingskin joints (SWJs) made with curved laminated composites are investigated. Three dimensional finite element analysis is employed to evaluate the natural frequencies and corresponding mode shapes of the joint structure considered. Virtual elements are implemented in the delamination region to prevent inter element penetration. The effectiveness of the finite element analysis technique used is validated with available results. Additionally, the effects of various parameters such as delamination size, curvature effect (shallowness angle), laminate stacking sequence, overlap length, and material anisotropy (modular ratio) on the free vibration responses of the curved SWJ are analyzed in details. The present delamination modeling and simulated results could serve as guidelines in designing curved laminated composite joint structures with/without delaminations. [ABSTRACT FROM AUTHOR]

A nine-noded isoparametric plate-bending element has been used for the analysis of free undamped vibration of isotropic and fiber reinforced laminated composite plates. The effect of shear deformation has been incorporated in the formulation by considering the first-order shear deformation theory for the analysis. An effective mass lumping scheme with rotary inertia has been recommended. Two types of mass lumping schemes have been formed. In one lumping scheme rotary inertia has also been introduced. Numerical examples of isotropic and composite rectangular plates having different fiber orientations angles, thickness ratios, and aspect ratio have been solved. Examples of plates having internal cutout and uniformly distributed mass on the plates have also been studied. The results obtained have been compared with the available published literature. The present results are very close to the analytical solutions. Few examples have been presented as new results. [ABSTRACT FROM AUTHOR]

Initiation and propagation of inter-laminar delamination in adhesive bonded spar wingskin joint (SWJ) made with laminated fibre-reinforced plastic (FRP) composite curved panels have been studied employing three-dimensional finite element analyses. In-plane and out-of-plane normal and shear stress distributions are seen to be highly three-dimensional in nature. Tsai-Wu coupled stress failure criteria have been employed to identify critical locations of onset of delamination-induced damage. This occurs underneath the toe-end of the spar overlap and at the inter-laminar surface between the first and second plies of the curved FRP wingskin panel. Significant edge effects on the joint strength have been observed due to the curvature geometry of the composite wingskin panels. Non-linear finite element analyses have been carried out for study of delamination propagation using contact and multi point constraint (MPC) elements. The use of contact elements prevents inter-penetration of delaminated surfaces. Whereas, sequential release of MPC elements facilitates computation of opening, sliding and cross-sliding modes of delamination-induced strain energy release rates (SERR) by using virtual crack closure technique. Variation in delamination lengths significantly effects the variation of peel and inter-laminar shear stresses and different modes of SERRs. Variations on the two delamination fronts are seen to be quite different indicating dis-similar propagation rates. The Mode I SERR (GI) predominantly governs the delamination propagation in the SWJ. [ABSTRACT FROM PUBLISHER]