Advanced Composites
Properties of fiber composites

Before a discussion of the various properties can take place, it is necessary to understand the anisotropic nature of fiber composites. Figure 1 below shows a small section of continuous fiber lamina. The fibers are aligned in one direction in the matrix. The direction parallel to the fibers is the "axial" direction and the direction perpendicular to the fiber is the transverse direction. The properties of the composite are dependent on the orientation of the fiber.

Figures 2, 3, 4, and 5 below show the comparisons of density, axial stiffness, specific stiffness, and coefficient of thermal expansion for various materials. Note that in the case of composite materials, the properties compared are the axial properties of the lamina.

As can be seen from the graphs above, composites enjoy substantial advantages in density, stiffness, and especially specific stiffness. Figure 5 shows a comparison of coefficients of thermal expansion (CTE). This is particularly important in the specification and design of components that experience high accelerations or where the design could benefit from minimized inertia.

Note that the standard modulus carbon fiber and ultra high modulus carbon fiber laminas actually have a negative CTE in the axial direction. This property makes it possible to design composite structures that are thermally stable.

These properties, along with the inherent corrosion resistance can be exploited to construct structural products whose performance cannot be matched by any known metal.

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