Dynamic mechanical analysis of fiber reinforced composites

Abstract Dynamic mechanical and thermal properties were determined for unidirectional epoxy/glass composites at various fiber orientation angles. Resonant frequency and relative logarithmic decrement were measured as functions of temperature. In low angle and longitudinal specimens, a transition was observed above the resin glass transition temperature which was manifested mechanically as anadditional damping peak and thermally as a change in the coefficient of thermal expansion. The new transition was attributed to a heterogeneous resin matrix induced by the fiber. The temperature span of the glass‐rubber relaxation was found to broaden with decreasing orientation angle, reflecting the growth of fiber contribution and exhibiting behavior similar to that of Young's modulus. The change in resonant frequency through the glass transition was greatest for samples of intermediate fiber angle, demonstrating behavior similar to that of the longitudinal shear modulus.