A comprehensive assessment of adhesively bonded joints between sandwich composite beams

Assessment of adhesively bonded joints between sandwich composite beams are presented in this thesis in three parts, each is concerned with a distinct aspect of the joint behaviour. In physical order, these include the deformations of the entire joint assembly, the state of stress in the joint overlap region, and the strain energy release at the crack-tip at the end of the overlap. Analytical models developed in this thesis, however, are not limited in their application to adhesive joint between sandwich beams. In each part of this thesis, the integrity of the proposed analytical models are tested against geometrically non-linear finite element models.;In this first part of this thesis, an analytical asymptotic model is presented for the analysis of balanced and unbalanced adhesively bonded joints. The model takes advantage of the asymptotic nature of the adhesive stress functions by eliminating exponentially small terms. Analysis of balanced and unbalanced adhesive joints is greatly simplified with negligible loss in accuracy. Accurate closed-form solutions for both adhesive peel and shear stresses are presented, providing an efficient analysis and design tool and a significant contribution to the literature on unbalanced adhesively bonded joints.;In the second part, the asymptotic model is extended to the analysis of strain energy release rates in adhesively bonded joints, using the crack closure concept. Closed-form expressions are presented for various joint types. The shear force and adhesive layer effects are included in the analysis, thus improving on currently available works in the literature. In joints with a long crack and a thin adhesive layer, the asymptotic model is shown to be in good agreement with classical beam theory models.;In the third part, deformations in adhesively bonded joints between sandwich beams are studied. Adherends are modeled as cylindrically bent plates on elastic foundations and the overlap section is treated as a single homogenous plate, thus simplifying the analysis procedure without compromising the accuracy of the results. Analysis of deformations in adhesive joints is undertaken primarily to produce estimates of the bending moments and shear forces at the ends of the overlap, which are used as boundary conditions in the asymptotic model. Results indicate that the sandwich core acts to reduce the severity of the edge moments and shear forces at the ends of the overlap. Furthermore, under certain conditions, the model is shown to be in perfect agreement with Goland and Reissner's model for balanced single-lap joints.;Adhesively bonded sandwich beams were tested statically and under fatigue to further verify the accuracy of the proposed analytical models and illustrate their applicability. The adhesive fracture toughness envelope was established experimentally to enable comparisons between analytical and experimental results on adhesively bonded sandwich beams. Fracture toughness of the adhesive is shown to be independent of the adhesive layer thickness and crack length.