Applications involving totally multidirectional applied stresses normally use discontinuous fibers, which are randomly oriented in the matrix material. Consideration of orientation and fiber length for a particular composites depends on the level and nature of the applied stress as well as fabrication cost. Fiber orientation in fiber reinforced composites. If the fibers are all parallel, the modulus of a fiber reinforced composite depends upon which direction you're measuring. E f is the modulus of the fiber along the length of the fiber.
V f is the volume percent occupied by the fibers.
Tensile strength and elastic modulus when fibers are parallel to the direction of stress. Figure 4. tensile strength and elastic modulus when fibers are perpendicular to the direction of stress. Fiber composite manufacturers often rotate layers of fibers to avoid directional variations in the modulus. The layers are stacked and cemented together such that the orientation of the high-strength direction varies with each successive layer. One example of a relatively complex structure is modern ski and another example is plywood.