Stress distribution in double-lap adhesive joints: Effect of adherend reinforcement layer

The present paper provides a model for the stress analysis of double-lap adhesive joints with multilayered inner adherend. The effect of the stiffness of the adherends on the distribution of stresses in the adhesive layer is investigated. Bonding adhesively materials with different stiffnesses (e.g. glass and plastic materials) leads to a concentration of stresses and therefore failure in the less stiff layer. Failure, therefore, occurs in the adherend cross-section instead of in the adhesive joint (stock-break failure mode). An innovative concept is here introduced for the double-lap adhesive joint by inserting a plate reinforcement in the less stiff substrate. Numerical and FEM analyses are used for validation. The results show that the insertion of a reinforcement plate (e.g. steel plate) in the middle of the inner adherend (e.g. plastic material) allows a better stress transmission to the outer adherends (e.g. glass). Four different configurations with various reinforcement thickness are investigated and the obtained adhesive stress distributions are compared to the results of FE analyses. In general, a good agreement is observed. This model demonstrates that peak stress in the adhesive layer could be significantly reduced by the layering of the inner adherend. Thus, the proposed concept provides a way to optimize double-lap adhesive joints for enhanced strength keeping the less stiff adherend in the bonding interface.