Effect of fiber‐aspect ratio and orientation on the stress‐strain behavior of aligned, short‐fiber‐reinforced, ductile epoxy

Abstract

AbstractIn the study of complex short‐fiber‐reinforced plastics behavior, it is helpful to begin with a well‐aligned short‐fiber system. This study isolates the effects of fiber‐aspect ratio and orientation distributions on the tensile stress‐ strain behavior and failure mechanisms for a system containing 50 vol% E‐glass fiber bundles in a ductileepoxy matrix. Using a system wherein the fiber orientation distribution was well‐characterized, it is shown that the fibers reinforced as bundles rather than as individual fibers. As the bundle‐aspect ratio varied from 185 to 557 for samples tasted in the longitudinal majoralignment direction, the modulus rose from 85 to 99 percent of the value for a continuous fiber system, while the strength rose only to about 60 percent of the continuous‐fiber system. The ductility of the matrix had no effect on the modulus or the longitudinal strengths, but the off‐axis strengths were significantly higher than has been reported for a comparable brittle‐matrix system. The effects of fiber orientation on modulus and strength were successfully fit with the Leknitskii and Azzi‐Tsai equations, respectively. SCanning electron micros‐copy showed excellent adhesion and no fiber brekage, except at the highest bundle‐aspect ratio. Even at off‐axis angles below 15°, a mixed mode failure mechanism occurs because of the fiber orientation distribution.