STRESS-FIELDS ON AND BENEATH THE SURFACE OF SHORT-FIBER-REINFORCED COMPOSITES AND THEIR FAILURE MECHANISMS

Stress distribution and failure mechanisms around the fiber ends were studied on the surface and in the interior of short-fiber-reinforced composites under uniaxial tensile loading. Microscopical observation of failure mechanisms in short-glass-fiber-reinforced poly(ethylene terephthalate) (SGFR/PET) showed that tensile cracks occurred mostly at the fiber ends on the surface and grew into the matrix. In the interior, however, shear yielding and shear cracking proceeded along the fiber/matrix interface in the fiber length direction with growth of shear bands around the fiber ends. The shear failures occurred preferentially for longer fibers. On the other hand, finite element calculation showed that octahedral shear stresses around the fiber ends in the interior were considerably higher than those on the surface. The shear stresses in the interior became much larger as the fiber aspect ratio increased. This calculation agreed qualitatively with the observation that these shear cracks appeared mostly in the interior.