Beaded fiber composites—Stiffness and strength modeling

Abstract

We present a theoretical analysis of the elastic stresses in a composite reinforced with beaded fibers by extending the classic Cox shear lag theory. The motivation for reinforcing a composite with beaded fibers is to improve both strength and toughness, two often conflicting properties. It is found that owing to their geometry beads intermittently placed on a fiber enhance fiber anchoring in the matrix, and can potentially dissipate energy by deforming the matrix during failure. The composite stiffness is shown to improve compared to a composite with beadless fibers, particularly when the beads are large and stiffer than the surrounding matrix. The stress profiles in the fiber, bead, matrix and along their respective interfaces incur periodic perturbations induced by the beads, modeled by Hill equation. For given elastic constants and bead geometry, these profiles reveal the weakest link loci in the structure, and consequently determine the composite strength and failure mode. A finite element analysis is presented that confirms our results. The bead-fiber and bead-matrix interfaces may be tuned by choice of materials and coatings to achieve desired mechanical properties.