Some fiber-resin composite interface work done at the Naval Research Laboratory is reviewed beginning with several applied studies and progressing to more fundamental work. Butadiyne (diacetylene) was evaluated as a novel carbon-fiber surface treatment applied via vapor deposition polymerization. Results of its application to high-strength carbon fibers, high-modulus carbon fibers, and aramid fibers are summarized. Reduction of carbon-fiber surface polarity by annealing under hydrogen was evaluated as a means to decrease the sensitivity of the interface to moisture.
In the above experiments the fragmentation test was used to determine relative levels of adhesion and the mechanisms of failure at the fiber/matrix interface. Comparisons of the adhesion of high-modulus and high-strength carbon fibers to epoxy and cyanate matrices were used to evaluate models for the fragmentation test. For high-modulus fibers the adhesion was poor and a friction factor approach may be suitable for modeling this type of interfacial failure. For high-strength fibers the adhesion was much higher and possibly limited by the shear properties of the matrix.
The simple mechanics models discussed previously do not explain adhesion changes where chemistry is the only variable. In a study of three matrix resins with comparable mechanical properties a linear dependence was shown between measured “good” adhesion and relative resin model compound basicity.