Effect of polyamide-6,6 (PA 66) nonwoven veils on the mechanical performance of carbon fiber/epoxy composites

Abstract

In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with polyamide-6,6 (PA 66) nonwoven veils at two different areal weight densities (17 and 50 gsm) to improve their delamination resistance against Mode-I loading. Mode-I fracture toughness (DCB), tensile, open hole tensile (OHT), flexural, compression, short beam shear (ILSS) and Charpy-impact tests were performed on the reference and PA 66 interleaved composite specimens. The DCB test results showed that the initiation and propagation Mode-I fracture toughness values of the composites were significantly improved by 84 and 171% using PA 66-17 gsm veils respectively, as compared to reference laminates. The use of denser PA 66-50 gsm veils in the interlaminar region led to higher improvement in fracture toughness values (349% for initiation and 718% for propagation) due to the higher amount of veil fibers involved in fiber bridging toughening mechanism. The incorporation of PA 66-50 gsm nonwoven veils also increased the ILSS and Charpy impact strength of the composites by 25 and 15%, respectively. On the other hand, the PA 66 veils reduced in-plane mechanical properties of CF/EP composites due to lower carbon fiber volume fraction and increased thickness.