Preparation of carbon fiber powder‐coated Z‐pins and experimental study on the mode I delamination toughening properties

In order to improve the adhesion property between the z-pin and laminate, carbon fiber powder coating technique for z-pins were developed. Four types of coating materials, 1 mm short chopped carbon fiber (CS), 50 mesh carbon fiber powder z-pins (CF), 400 mesh carbon fiber powder (CP), and carbon nanotubes (CN), were coated on an impregnated fiber bundle before the curing of the resin of the z-pins. The diameters of the four types of coated z-pins were increased from 0.50 to 0.61 mm, 0.57 mm, 0.58 mm, and 0.54 mm, separately. To characterize the adhesion property of the z-pin/laminate, single z-pin pull-out tests were conducted. The results indicated that carbon fiber powder coating could improve the interfacial adhesion property of the z-pin/laminate effectively. The interfacial shear strength was increased around 1/3. CS, CF, and CP improved the mechanical interlock and bridging effect of the interface, while CN enhanced the adhesion effect of the reinforcing mode. To examine the interlaminar performance of the reinforced laminate, we also conducted double cantilever beam tests. It was found that the coated z-pin, which was related to better interfacial adhesion property, corresponded to higher mode I interlaminar fracture toughness of z-pinned laminates. (C) 2015 Society of Plastics Engineers