Composite materials have been used in many structural applications because of their superior properties. Although composites are less sensitive to deformation, their increased use has emphasized that their deformation behaviours and hence deformation analyses are more complex than for structures of uniform composition. Deformation patterns contingent upon fatigue properties of composites may vary significantly because of the large differences in properties of the fibres and matrix, and the compositions of their sub-constituents. These complexities introduce major deficiencies to methods for composite materials, which often force large factors of safety to be adopted in designs. Consequently, composite structures used in fatigue applications are generally over-designed to eliminate catastrophic failure and are therefore heavier and more costly.