Determination Optimmum Relative Bonded Length and Ratio of Adherend Thickness to Adhesive Layer Thickness in Composite Adhesive Joints

Adhesive joints due to having, wide bonding area and low stress concentration factor and capability of joining and sealing simultaneously are the most suitable joints in composite structures. Performance of adhesive joints severely influenced by the geometry and types of these joints, so that in this paper, influences of bonded length, with respect to total length of composite adherends for two common types of single lap and double lap adhesive joints, and effects of relative thicknesses of these adherend to adhesive layer thickness, on stress distributions and maximum stresses in adhesive layer are investigated. For these purpose at first, a mathematical modeling for analysis of adhesive joints with composite adherends is present. In this model adherends are orthotropic laminates that obeyed special case of classical lamination theory. The stacking sequences can be either symmetrically or asymmetrically. Adhesive layer(s) is (are) homogenous and isotropic materials. They are modeled as continuously distributed tension/compression and shear springs. Then by using this mathematical modeling, the governing equations of the modeling are solved analytically for various specific bonding length (bonded length, with respect to total length of composite adherends) and specific adherend thickness (relative thickness of the adherend to adhesive layer thickness), adhesive layer(s) peel and shear stress distributions and the maximum magnitudes of these stresses, for each case are determined, and by investigating these results, the optimum specific bonding length and specific adherend thickness are recommended for the single lap and double lap composite adhesive joints. Also it is considerable that, the optimum point of the specific bonding length may not be the optimum point of the specific adherend thickness, so that, in this paper, 3D peel and shear stress diagrams with these two variable are investigated too, for cases that designer can vary bonding length and adherend (or adhesive layer thickness) together.