Table of Contents

Materials and Structure




In addition to being dependent on the fiber volume fraction, the Young's modulus of a uniaxial composite is dependent on the angle the fibers make with respect to the tensile stress direction. The diagram shows the modulus behavior for a unidirectional lamina of glass fibers in a polyester resin matrix. The volume fraction of the fibers is 0.3. The Young's modulus is highly directional (red line), and this can be exploited in design if a different mechanical response is desired in orthogonal directions.

The semicircular curve for random-orientation short fibers in the same matrix, shows that the maximum modulus is reduced by about a factor of two but that the material modulus is direction independent within the plane of the lamina. The cost of manufacturing a chopped fiber lamina is also less than that of a uniaxial one, and cost considerations may dominate the design choice, particularly if anisotropic properties offer no performance advantage.

From: Hull, "An Introduction to Composite Materials,"
Cambridge (1992)