Determination of interface integrity in high volume fraction polymer composites at all strain levels

In fiber-reinforced composites, the mechanical performance is strongly dependent upon the quality of fiber/matrix interface. In the present work, a novel technique is presented whereby all important interface parameters of high volume fraction composites are determined in situ on standard tensile coupons. The method involves the introduction of a small surgical cut to the upper ply of a unidirectional aramid/epoxy laminate prior to vacuum bagging. During the curing procedure and subsequent consolidation in an autoclave, the resin penetrates the area of the cut and thus no effect to the integrity of the composite is observed. The stress transfer profiles during mechanical loading emanating from the fiber break(s) can be obtained by means of the technique of laser Raman microscopy. The technique allows the determination of the maximum interfacial shear stress at all far-field strain levels and therefore presents the only alternative for the accurate estimation of interface integrity in high volume fraction polymer composites.