Stress analyses around holes in composite laminates using boundary elementmethod

A three-dimensional (3D) boundary element method (BEM) is developed for the analysis of composite laminates with holes. Instead of using Kelvin-type G reen's functions of anisotropic infinite space, 3D layered Green's function s with the materials of each layer being generally anisotropic, derived rec ently in the Fourier transform domain, are implemented into a 3D BEM formul ation. A novel numerical algorithm is designed to calculate layered Green's functions efficiently. It should be noted that since layered Green's funct ions satisfy exactly the continuity conditions along the interfaces and top and bottom free surfaces a priori, the model becomes truly 2D and discreti zation is only needed along the hole surface and prescribed traction and/or displacement boundaries. To test the validity and accuracy of the proposed method, the present layered BEM formulation is applied to the problem of a n infinite anisotropic plate with a circular hole where the analytical solu tion is available. It is found that even with a very coarse mesh, the prese nt BEM can predict the hoop stress very accurately along the hole surface. The BEM formulation is then applied to analyze two composite laminates (90/ 0)(s) and (-45/45)(s), under a remote inplane strain, that have been studie d previously with different approaches. For the (90/0)(s) case, the hoop st resses along the hole surface predicted by the present layered BEM formulat ion are in very close agreement with the previous results. For the (-45/45) (s) case, however, it is found that a nearly converged solution (less than 5% convergence by doubling the mesh) by the present method is at significan t variance with the previous ones that are lack-of-convergence checks. It c an be expected that for designing the bolted joints of composites with many layers, a computational tool developed based on the present techniques wou ld be robust and offer a much better solution with regard to accuracy, vers atility and design cycle time. (C) 2001 Elsevier Science Ltd, All rights re served.