Preparation of polyvinyl alcohol-matrix z-pins and tests of their piercing properties.

In this study, we developed a molding process for a new type of z-pin applicable to C/C composites. Polyvinyl alcohol (PVA) was adopted as the matrix of z-pins because it has few solid residues when subjected to an inert high-temperature environment. A highly concentrated PVA aqueous solution was prepared to impregnate the carbon fiber bundle. The draw forming method from small-hole-cavity dies was used to mold the PVA-matrix z-pins. Four z-pins with different resin content were made by four dies with the cavity diameters of 0.50, 0.60, 0.70 and 0.80 mm, respectively. The piercing processes and properties of the z-pins were analyzed by piercing them into carbon fiber laminated fabrics. The results showed that the measured value of the PVA resin volume content of the z-pins was slightly larger than the theoretical value. And the z-pin prepared in the molding die with a cavity diameter of 0.70 mm (P7) exhibited the best piercing property with a resin volume content of 45.6%. The maximum compressive stress in the whole piercing process of P7 was the lowest as compared to the z-pins molded by the other dies, and little damage to the piercing tip of P7 was observed after the penetration. In addition, the z-pins can fully pierce laminated fabrics with a thickness of 9 mm. [ABSTRACT FROM AUTHOR]