A Photoelastic Analysis of Fiber Discontinuities in Composite Materials

Abstract

A two-dimensional photoelastic stress analysis of various dis continuous fiber-reinforced composite material configurations is described. Models were constructed from two different photoelastic materials, representing a fiber/matrix modulus of elasticity ratio of 40, and making possible maximum shear stress measurements in both matrix and fibers. Each fiber discontinuity which was investi gated was flanked by continuous fibers, with lateral spacings repre senting 16 and 45 volume percent fiber. Matrix stress concentrations (defined as the maximum shear stress near a fiber end divided by the maximum shear stress remote from the discontinuity) are re ported as a function of longitudinal spacing, eccentricity and overlap of fiber ends. Values as high as 13 were obtained. The effects of lateral fiber spacing on matrix stress concentration and on critical fiber aspect ratio were observed. The presence of extremely high stress gradients in the matrix near fiber ends suggested the im portance of having good matrix ductility in discontinuous fiber- reinforced composites.