Effect of Patch Interface Strengthening on Mechanical Properties of Epoxy/Carbon Fiber Sheet by Double-Sided Patching

Abstract

To repair the damage to the epoxy/carbon fiber laminate, a single-lap test was performed between sulfuric acid anodized aluminum plate and carbon fiber laminate to study the effect of the anodized layer on the interlaminar shear strength. Then, carbon fiber laminates were prepared by wet-laying method to simulate the damage caused by penetrating cracks, and double-sided adhesive sheets were made from 0.5[Formula: see text]mm thick 2024-T3 aluminum alloy and carbon fiber laminates to match the thickness and material of the simulated damage plate. The adhesive matrix used was E51 bisphenol-A epoxy resin with 1.5[Formula: see text]wt.% nanorubber added for modification and toughening. After double-sided patching, tensile tests were performed to investigate the effect of different materials on the tensile strength of double-sided adhesive patches. We observed SEM images of the fracture surface of the patch after tensile failure and analyzed the strengthening mechanisms of different material patches. The results show that the shear strength between the single-layer sulfuric acid anodized aluminum plate and the carbon fiber laminate is 9.792 MPa, which is 61.5% higher than the shear strength of the nonanodized aluminum plate. The tensile strength of the 2024-T3 aluminum patch specimen is 271.83 MPa, which is 48.43% and 23.97% higher than the perforated specimen without patch and the specimen with carbon fiber laminate patch, respectively, and reaches 72.56% of the undamaged carbon fiber laminate. The specimens with aluminum plate patches showed a maximum bending strength of 616.47 MPa, which increased by 70.83% compared to the 360.875 MPa of the perforated specimens. The maximum bending strength of the aluminum plate patch specimen reached 74.76% of that of the undamaged specimen. However, the maximum bending strength of the composite patch specimen is as high as 1101.9 MPa, far exceeding that of other samples. Due to the poor toughness of the sample, it cannot withstand large strains. The addition of 1.5[Formula: see text]wt.% nanorubber results in shear yield bands and induces silver grains to absorb a large amount of energy during stress deformation.