Interphase Bond Strength and Energy Absorption of Injection-Molded Rubber-Coated Glass/Nylon Composites

The use of a thin rubber coating on the fiber in a fibrous composite has been shown to increase the composite low-speed impact resistance [1,2]. The coating used was very thin compared to the fiber diameter, in order to preserve the other composite properties. From elastic consideration, the thin rubber coating was understood to have a direct effect upon the reduction of the stress concentration in the region near the fiber/matrix interface, especially at the chopped fiber end or at the matrix crack front reaching the fiber [3,4]. If the possible existence of localized high stress zones is reduced, the material can be subjected to higher loading before global failure occurs. With the rub ber coating the high stress zones inside the material can spread out to a larger volume. There will be less chance for local damage to initiate under the same loading level. The material will therefore exhibit higher resistance to failure, i.e., it will absorb more energy before failure. Three injection-molded glass/nylon composites were tested for tensile fail ing energy. One is reinforced with bare chopped fibers and the other two are with rubber- coated fibers. Tensile experiments showed significant increase of energy absorption in one sample with a rubber coating. Micrograph study was extensively carried out on the failed samples to identify the parameters of this desirable consequence. The rupture of the rub ber interphase and the limited plastic flow of the nylon matrix on the fractured surface of failed specimens were clearly evidenced. Meanwhile, interfacial bonding measured through microdebonding tests [4] revealed reasonable relation of the characteristic inter facial bonding and the energy absorption.