| The elastic behaviour of adhesively bonded balanced and unbalanced single-lap joints has been studied analytically, numerically and experimentally. The main focus is the analysis of the overlap edge loading conditions and adhesive stresses within the bondline of aluminum-to-aluminum (balanced) and composite-to-aluminum (unbalanced) joints. While balanced joints are widely used, unbalanced joints are increasingly needed in aerospace and civil engineering applications.; In the theoretical study, an analytical beam model for predicting the overlap edge bending moment, k, and adhesive stresses for the balanced single-lap joints have been derived. In addition, three simplified mathematical (no stress analysis) solutions for predicting k have also been proposed for balanced single-lap joints since the currently available closed form solutions are complex and difficult to apply. The proposed closed-form model applies exact displacement boundary conditions and also accounts for the effects of material properties and geometry of both the adhesive layer and adherends.; The current model, other closed-form models for balanced joints available in the literature, and the mathematical solutions have been compared with the earliest model proposed by Goland-Reissner (1944). Although the three simplified k solutions do not consider the effects of adhesive material properties, their predictions agree reasonably well with the available closed-form models under certain conditions.; A separate closed-form model to predict the transverse deformation of unbalanced single-lap joints has also been derived. The solutions for the bending moments are comparable to the model proposed by Cheng et al. (1991). Since the shear force analysis at the overlap edges by Cheng et al. (1991) was inaccurate, the author also corrected the expression for shear force calculation. Other errors in the derivations by researchers such as Hart-Smith (1973) were found for the balanced and unbalanced joints and have been corrected for in the present study.; Extensive numerical simulations using a two dimensional geometrically nonlinear finite element code, (ANSYS version 5.3), under both plane strain and plane stress conditions, have also been conducted in this work. The effects of rotation and no-rotation boundary conditions, filleted and unfilleted joint geometries, and adhesive modulus on the overlap edge bending moments as well as the adhesive stresses have been investigated for both the balanced and unbalanced configurations. The results are compared with existing theoretical beam models including the proposed one.; In the experimental study, tensile testing was performed on both balanced and unbalanced single-lap joints with fillets. The joints were strain gauged to measure the strain along the overlap region as well as at the surfaces of the unbonded adherend section during deformation. It was not physically possible to measure adhesive stresses along the very thin adhesive layer. Due to the limited number of test specimens, the results should be considered as phenomenological. An experimental error analysis for 95% confidence was conducted. The experimental results were found, in most cases, to compare fairly well with the finite element predictions of strain distributions for both types of joints. |
