Composite Materials

· The modulus of the laminate is a good measure of the degree of damage produced by fatigue. The diagram shows the dependence of the composite modulus on cycle ratio.

· Transverse cracks in the laminae and inter-laminate debonding are responsible for the range of modulus decrease. Once the matrix has fractured the fibers carry the applied cyclic load and these may also suffer fatigue if the applied stress is high enough.
· Fiber fatigue continues at constant modulus until enough fibers have broken to cause laminate failure.

From: Schaffer, et al, "The Science & Design of Engineering Materials," Irwin (1995)