Effect of hot needle punching on bending and inter-laminar characteristics of CF/PA6 composite

Abstract

The purpose of this study is to investigate how affect the hot needle punching on bending strength and inter-laminar fracture toughness of CFRTP. Four types of needle in which tip shape were different was used to investigate the effect of needle shape on bending strength and interlaminar fracture toughness of CFRTP. CFRTP specimen was heated to soften the matrix of PA6, and then needle punching was conducted to specific number of times per unit area. The bending characteristics and interlaminar fracture toughness of CFRTP were evaluated by four point bending test and double cantilever beam (DCB) test, respectively. Test results showed that when punching was done using a needle with a notch at the tip, it resulted in the realignment of the yarn fibers along the out-plane direction of the punched specimen. It also led to the breakage of the fibers, owing to excessive bending. Moreover, due to the high viscosity of the matrix resin, the void was generated when the needle was pulled out from the composite. The interlaminar fracture toughness of the CFRTP specimens improved when punching was performed at stab density of 12 cm^-2 or more. Finally this paper revealed that the mode I fracture toughness of the needle-punched CFRTP specimens is dependent on both of crack bridging of the realigned fiber and pin-like resin structure.