Stress analysis and testing of parallel and tapered adhesive butt joints

Abstract

A correlation between numerical results obtained by the finite element (FE) method and experimental data for parallel and tapered butt joints under tensile load was investigated. Two linear FE simulations were constructed for both joints and the numerical results were used in understanding the ultimate strength and failure modes. The data provided the ultimate tensile strength and failure modes for various thicknesses of polyurethane adhesive bonded between polycarbonate and aluminum adherends. The numerical and test data results show that a thinner parallel adhesive layer leads to a stronger joint. An optimum adhesive layer thickness was found for the tapered configuration (0.4-0.5 mm). This thickness was achieved when the stress value and its gradient were distributed in an optimal ratio. Then the mode of failure was changed from interfacial to cohesive. The enhanced sensitivity found for the tapered joint strength as a function of its thickness leads to the conclusion that in real bonded structures it should be avoided. In addition to other important parameters, i.e. surface treatment and material properties which ensure high strength and durable adhesive joints, any existing tapered angle of the adhesive layer should be minimized.