Dynamic Analysis of Interfacial Cracks in Composite Laminates

184 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.The interfacial crack in composite laminates has been of great interest as composite materials are widely used today. In this paper, the order of dynamic stress singularity of interfacial cracks is derived, and a hybrid finite element method is successfully developed for this problem. Both the cases of open and closed cracks are considered. An integral transform, the Wiener-Hopf technique, and an asymptotic theory have been used for deriving the orders of stress singularity of interfacial cracks. The crack-tip elements in anisotropic materials are formulated by employing Lekhnitskii's stress functions and the variational principles of a hybrid functional. An iterative scheme for determining the closure size of a partially closed crack is proposed. Solutions for the orders of stress singularity of interfacial cracks in graphite-epoxy composites with different lamination variables and crack surface conditions agree well with the reference solutions. For the problem of an interfacial crack between two dissimilar anisotropic half spaces, finite element solutions are found very close to the exact solutions. Effects of element size, aspect ratio, and eigenfunction truncation of the crack-tip elements have been studied. Solutions for several delamination problems of practical interest are also presented by using hybrid crack-tip elements. Results of this study show that the Wiener-Hopf technique is a suitable method for investigating the dynamic behavior of interfacial cracks and that the hybrid crack-tip elements provide efficient and accurate numerical methods for studying delamination problems of composites.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD