Effect of spew geometry on stresses in single lap adhesive joints

Spew is defined as the portion of adhesive that is squeezed out from the lap area and forms a bead at the lap ends as the two substrates are assembled. Spew is always present in an adhesive joint, but is usually neglected in the stress analysis of adhesively bonded joints. As known, the presence of spews can reduce peak stresses and therefore increase the joint strength. The reduction in peak stresses, however, is not only related to the presence of spew, but also to the shape and size of the spew. This paper investigates how the adhesive spew geometry affects the peak stresses and stress distributions in adhesively bonded single lap joints. The stresses in adhesively bonded single-lap joints with various spew geometries was determined using finite-element techniques. A linear two-dimensional plain strain analysis with isotropic materials were performed using the ANSYS finite element software. The stress distribution across the lap length at the interface for joints with different spew geometries was determined and compared to that of the square ended single lap joint (i.e. joint without spew). Peak stresses were also determined and the percent reduction in stresses from the square ended joint was calculated for each spew shape. It is shown that by shaping the spew to provide a smoother transition in joint geometry significantly reduces the stress concentrations at the substrate–adhesive interface. Furthermore, increasing the size of the spew also reduces peak stress concentrations.