Nanostructured ZnO Interphase for Carbon Fiber Reinforced Composites with Strain Rate Tailored Interfacial Strength

Composite materials designed for ballistic applications typically require fiber-matrix interfacial properties which are considerably different than those used in more common structural applications. Ballistic composites are usually benefited through the use of a weaker interface that allows the high tenacity of the fiber to be utilized for energy absorption, whereas structural composites require strong interfaces to ensure materials which do not easily delaminate or experience cracking. Here, the multifunctionality of a zinc oxide (ZnO) interphase through a tailored interfacial shear strength (IFSS) as a function of strain rate is demonstrated. Both ZnO nanowires (NWs) and nanoparticles (NPs) are shown through variable strain rate pullout to enable tailored behavior with the NWs producing an 87% increase in IFSS over untreated fibers under quasi-static loading, and 53% lower interfacial shear strength than untreated fibers at 2200 s(-1). The reduced interfacial strength under dynamic loading conditions is attributed to the polymer's viscoelasticity, as matrix stiffening effects reduce the NWs' functional gradient, causing brittle failure of the ceramic interphase. The results demonstrate the potential for ZnO NWs and NPs to enable the tailored design of interfaces and to realize multifunctional materials with optimal behavior under both static and dynamic loading conditions.