Peak stresses in adhesive step lap joints with voids

In composite to metal joining applications, such as in aerospace and high technology structural components, adhesive bonded joints are finding increased use because of their many advantages in terms of strength to weight ratio, stress distribution, design flexibility, cost reduction and simplicity of fabrication. It is known however, that defects in the adhesive can severely reduce the bond strength. The presence of voids or disbond type flaws in the adhesive will increase the peak stress levels which occur at the joint ends and near the flaw itself. In the present work, the stresses in a step lap joint with a void are shown to depend on certain governing parameters which completely characterize the problem. Based on appropriate equilibrium, stress-strain (plane strain) and strain displacement relations, the problem is reduced to a second order differential equation for the axial load in one of the adherends. A convenient non dimensionalization of quantities in the equations leads to three parameters which uniquely define the stress distribution in the joint. In this sense, the curves obtained for the non dimensional stresses are universal and parameter dependent, and therefore, very useful for design or testing purposes.