Fatigue life prediction of matrix dominated polymer composite materials

Fatigue life prediction is investigated analytically for matrix dominated p olymer composite laminates having nonlinear stress/strain response, based o n the fatigue modulus concept. Fatigue modulus degradation rate at any fati gue cycle was assumed as a power function of number of fatigue cycles. A ne w stress function describing the relation of initial fatigue modulus and el astic modulus was used to account for material non-linearity at the first c ycle. It was assumed that fatigue modulus at failure is proportional to the applied stress level. A new fatigue life prediction equation as a function of applied stress is proposed. The prediction was verified experimentally using cross-ply carbon/epoxy laminate (CFRP) tube under torsional fatigue l oading. It is shown that the proposed equation has wide applicability and a grees well with experimental data.