A STUDY OF STRESS-DISTRIBUTION IN MODEL COMPOSITES BY USING FINITE-ELEMENT ANALYSIS .1. END EFFECTS

The stress distribution along a fiber in model polymer composites has been calculated using a finite-element analysis technique. Earlier experimental studies suggested that the stress distribution for fibers with tapered ends is much more efficient in carrying an external load than is the case for fibers with blunt ends. Both thermal residual (compressive) stress and tensile stress distributions along the reinforcement fiber have been measured with high sensitivity and spatial resolution. For fibers with blunt ends, the measured stress distribution agrees well with the stress distribution expected for an idealized shear-lag model. For tapered fibers, the stress distribution measured is a constant along the fiber and a critical length was not found. Finite-element calculations agree well with these experimental data. In addition, the stress distribution in the fiber, i.e., the radial dependence and the relative strain in both the fiber and matrix, was calculated. A detailed description of possible failure modes for the discontinuous fiber composites is provided based mainly on the finite-element calculation.