Adhesively bonded single lap joints with non-flat interfaces

A series of experiments and detailed finite element simulations were carried out to study the performance of single lap joints with non-flat interfaces loaded at a small angle to the mean bond plane. In the experimental part, fiber reinforced epoxy composite adherends with sinusoidal bonding surfaces (but no change to the exterior sample dimensions) were fabricated in a purpose-built mold. This construction method allowed the fibers to follow the sinusoidal profile for maximum strength. Then the sinusoidal surfaces were joined by a controlled-thickness layer of epoxy. Single lap joints with a flat interface were also fabricated using the same composite material and with the same overall shape. The experiments showed that the interface non-flatness has significant effect on the mechanical behavior and strength of the bonded joints. Finite element simulations of a simplified two-dimensional model with isotropic adherends were also carried out to estimate the distribution of shear and peeling stresses along the bonded joints, and the results were related to the experimental observations. Parametric variations were studied via FEA to highlight the role of interface shape, adhesive elastic modulus and a central void size on the distribution of stresses, and inherently the overall strength and behavior of the bonded joints.