Bone-shaped short fiber composites—an overview

In recent years, a new class of short fiber composites, in which the ends of the short fibers were enlarged, have been studied. Because of their geometry, these short fibers were named bone-shaped short (BSS) fibers. It was found in several composite systems that the BSS fibers can simultaneously improve both the strength and toughness of composites, and the mechanisms for such improvements vary with mechanical properties of the composite constituents. The strength increase resulted from the effective load transfer from the matrix to the fibers through mechanical interlocking at the enlarged fiber ends. The toughness increase resulted from one or several mechanisms, including: reduction in stress concentration in a brittle fiber reinforced composite with weak fiber/matrix interfacial bonding; higher fiber pullout resistance when the BSS fibers bridging a matrix crack are pulled out, with the enlarged ends attached and perhaps deformed; and plastic deformation of ductile fibers. Both experimental and theoretical studies have been conducted on composite mechanical properties and fractography, fiber pullout, and stress analysis. This paper reviews recent developments in BSS-fiber composites as well as discusses current issues and future directions in this emerging field.