Enhancement of the in-plane and pin-load bearing behavior of a quasi-isotropic carbon fiber/epoxy matrix multi-scale laminate by modifying the fiber-matrix interphase using graphene nanoplatelets

Abstract

The present work examines the effect of incorporating two different concentrations, 0.1% and 0.25%, of silane-functionalized graphene nanoplatelets GnP-GPTMS onto the carbon fiber surface of a quasi-isotropic laminate with the aim to enhance both, the laminate in-plane and the bearing strength, in a pin-loaded joint. Delamination damage modes associated with high-stress gradients were also suppressed in the in-plane loaded laminates, significantly increasing load-carrying capability. The bearing strength of a pin-loaded hole is correlated to the tensile, compression, and shear properties. The results showed an improvement of 13.8% in tensile strength for the 0.1% GnP-GPTMS concentration, as well as 17.3% for compressive strength, while for shear strength, the improvement was 11.89% for the laminate. On the other hand, the behavior of the material in the pin-loaded joint showed an increase of 10.83% for the bearing strength with the 0.1% GnP-GPTMS, fiber surface treatment. Distinct differences were noticed between the tensile stress-loaded area and the area of the residual impression of the pin in the failure mode between the only-resin treated carbon fiber composites and GnPs treated fibers. It was evident, that the interfacial shear strength (IFSS) played an important role on the failure mode. In the compression area in the pin-loaded region, there was a marked presence of a permanent deformation in the matrix. With a closer look at the local failure phenomena at the compression loaded area, there was no fiber kinking and the degree of matrix plasticity disappeared according to the level of interfacial adhesion.