Impact resistance of composite to aluminum single lap joints reinforced with graphene doped nylon 6.6 nanofibers

Abstract

In this study, the low velocity impact resistance of pure and modified epoxy adhesives for single lap joints between aluminum and carbon epoxy composites was investigated. Epoxy resin was used as the adhesive, and pure epoxy resin was modified by adding graphene-doped nylon 6.6 nanofibers (1%, 3% and 5% by weight) and pure nylon 6.6 nanofibers produced by electrospinning. These nanofibers are reinforced to aluminum-composite single lap joints as a second interface according to ASTM D1002-10 standard. Thus, single lap joints were prepared using 5 different adhesives. To create the impact effect, some joints were subjected to impact at a low velocity (1.04 m/s). Then, all impacted and non-impacted samples were subjected to single lap shear testing at room temperature and constant load to determine the impact resistance. While the non-impact lap shear strength of the pure epoxy adhesive samples was 6.81 MPa, the non-impact shear strength of the samples using pure nanofiber reinforced epoxy adhesive increased by 71.3% to 11.67 MPa compared to the pure epoxy adhesive. When comparing the post-impact failure loads, it was determined that the addition of graphene increases the impact resistance. Furthermore, adhesive surfaces were examined by scanning electron microscopy (SEM) for damage analysis after the tensile tests and toughening mechanisms such as bridging, adhesive crack formation, nanofibers breakage was determined in epoxy adhesives reinforced nanofiber with graphene in different proportions by weight. In addition, the glass transition temperature, melting temperature, thermal decomposition temperature and mass loss of epoxy resin, and graphene doped/undoped N6.6 nanofiber-reinforced epoxy adhesives were analyzed by Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) and it was determined that the addition of 3% GNP to N6.6 nanofiber reinforcement increased the thermal stability by 12.4%, the addition of 1% GNP to N6.6 nanofiber reinforcement increased the thermal resistance (glass transition temperature) by 34.9% compared pure epoxy.