FIBER FRACTURE IN HYBRID COMPOSITE SYSTEMS

Conventional and hybrid micro-composites consisting of up to nine single fibers in Epon 828/Versamid 140 epoxy were constructed and pulled in uniaxial tension. The coordination of fiber fractures for each system was studied as a function of interfiber spacing. E-glass, AS-4 and IM6-G carbon, and Kevlar-49 fibers were used. It was shown that fiber fracture occurred in a random pattern when fiber spacing was more than eight fiber diameters. When the fiber spacing was less than eight fiber diameters there was coordination of fractures in adjacent fibers, with increased adhesion resulting in stronger coordination. The AS-4/Kevlar-49 hybrid system exhibited the least amount of coordinated fracture. A computer model of the hybrid effect, based on local load sharing principles, predicted similar strength enhancement of the stiffer fibers in hybrid composites as other authors have found experimentally. It was concluded that the hybrid effect can be attributed to load sharing between high and low modulus fibers in hybrid composites.