The analysis and design of adhesively bonded composite structures
Adhesively bonded structures offer an attractive alternative to the historically prevalent bolted/riveted approaches to joining load bearing elements. Adhesively bonded assemblies allow for a gradual transfer of load from one structural element to another and a reduction of stress concentrations arising from material discontinuities inherent to mechanical fastening methods.
Several fundamental questions remain regarding the behavior of axially loaded lap shear joints. These issues are: the underestimation of the adhesive layer stresses by the various canonical literature models, the existence and magnitude of longitudinal tensile stresses in the adhesive layer, the existence of stress singularities at the corners of adhesive layers, and the effectiveness of asymmetrically designed adherends for reduction of adhesive layer peel stresses.
To investigate these issues, a high-order approximate elasticity solution for the adhesive layer is developed. This linear elastic model satisfies all natural/essential boundary conditions and is continuous over the entire domain (including the sharp comers).
Using this adhesive model, we find that the axial tensile stresses are negligible and that the shear stress state does not vary through the thickness of the adhesive layer. It is also found that the literature models underestimate the adhesive peel stresses by nearly 10% due the plane-stress assumptions commonly invoked.
Parametric studies are performed for adhesively bonded composite beam and shell structures. Once the influences of all geometric and material stiffness parameters are ascertained, guidelines are proposed for improved joint designs to reduce adhesive layer peel stresses. Using these design guidelines, an evaluation of midplane asymmetric beam and shell adherend architectures is performed. Improved beam adherend architectures and shell adherend architectures are identified.