Composite Materials
Composite materials have their microstructure designed in terms of their macroscopic constituents, e.g. fibers in a homogeneous matrix material. By controlling the choice of fibers, their volume fraction, and alignment, the mechanical properties may be tailored to meet specific design requirements.

The diagram (a) shows a 'uniaxial fiber-reinforced' composite material, and (b) shows how the stress on the composite is carried by the fibers and the matrix. In normal situations, the fiber has a larger Young's modulus than the matrix, and for the continuous fibers shown, where the strain is the same in the matrix and the fiber, the fiber stress is higher than the

From: McMahon and Graham, :"The Bicycle and the Walkman," Merion (1992)

matrix stress. The Young's modulus of the Composite is given by the 'rule of mixtures' i.e. E_C = E_F V_F + E_M V_M , also ( V_M + V_F ) = 1 or V_M = (1 - V_F ). The elastic modulus along the fiber direction can be controlled by selecting the volume fraction of the fibers.