Damage onset in CFRP single lap joint for DD and QUAD laminates

The most usual layup in composite design, namely QUAD, has the plies oriented at 0°, 90° and ±45°. Alternatively, double-double (DD) laminates were recently proposed, where plies are oriented at ±Φ and ±Ψ, allowing optimized application and improving structural response, since Φ and Ψ continuous variables ranging between 0° and 90°. The present research is the first effort to compare the response of QUAD and DD laminates in single lap joints. A finite element model is developed using the software Ansys. The damage onset is evaluated considering the Drucker-Prager criterion for the adhesive and Tsai-Wu criterion for the laminate. A QUAD laminate is selected and DD layups are evaluated considering the stiffness equivalence. The results indicate that all DD layups improve the joint damage onset, obtaining forces up to 25 % higher than for the equivalent QUAD and smother transition of the stress invariants.