An experimental and theoretical study of the stress transfer problem in fibrous composites

The problem of efficient stress transfer in two-phase composites is very intriguing as it is a prerequisite for the attainment of satisfactory mechanical performance in these materials. Many micromechanical models are now available for the prediction of the stress distribution on either phase or at the interface. Some of the existing models are based on poor assumptions while others are too complex to be applied directly without prior knowledge of all the elastic constants of the constituent materials and their inter-dispersion in the composite. In this paper, an attempt is made to revisit the shear-lag type of model applying it to a specific class of two-phase materials, that of long-fiber polymer composites. The experimental tool used to verify the theoretical stress distributions is the technique of laser Raman microscopy (LRM). By introducing, a local fiber discontinuity in a composite of high volume fraction we could determine both the axial fiber build-up and the corresponding interfacial shear-stress distribution at all strain levels using LRM. The results are compared to the theoretical shear-lag curves (elastic region) and useful conclusions are drawn for the universality of these models and their applicability to high volume fraction polymer composites.