Fatigue life prediction of matrix dominated polymer composite materials

Abstract

Fatigue life prediction is investigated analytically for matrix dominated polymer composite laminates having nonlinear stress/strain response, based on the fatigue modulus concept. Fatigue modulus degradation rate at any fatigue cycle was assumed as a power function of number of fatigue cycles. A new stress function describing the relation of initial fatigue modulus and elastic modulus was used to account for material non-linearity at the first cycle. 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 loading. It is shown that the proposed equation has wide applicability and agrees well with experimental data.