Effects of laminate carbon/epoxy composite patches on the strength of double-strap adhesive joints: Experimental and numerical analysis

• Fiber orientation angles of the patches markedly affected the failure load of joints.
• Ply stacking sequences have a significant effect on the stress distributions.
• Shear stress distributions are extremely sensitive to these 3-D effects.
• Fiber orientation angles of the patches markedly affected failure mode.

In this study, mechanical properties of double-strap joints with aluminum or composite patches of different orientation angles at their overlap area were investigated under tensile loading. For this purpose, AA2024-T3 aluminum was used as adherend, while patches were either AA2024-T3 aluminum or 16-ply laminate of carbon/epoxy composite with five different orientation angles ([0]16, [90]16, [0/90]8, [45/−45]8, [0/45/−45/90]4). A two-part paste adhesive (DP 460) was used to bond adherend and patches. Six different types of joint samples were subjected to tensile loading. The effect of patch material on failure load and stress distribution was examined experimentally and numerically. As a result, it was concluded that the data obtained from 3-D finite element analysis were coherent with experimental results and additional to that fiber orientation angles of the patches markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite.