Fatigue Life Prediction Method Of CFRP Laminates

Fiber reinforced composites have been widely used in aerospace,automotive vehicle,wind power generation and other fields because of their advantages of high strength-to-weight,high stiffness-to-weigh properties and high temperature resistance.In the structural design of composites,not only the static mechanical properties of the material should be taken into account,but also serious damage should not occur under the cyclic fatigue loading.The generation,expansion and accumulation of fatigue damage tend to aggravate the environmental corrosion and stress corrosion of materials,which further result in a sharp loss of strength and stiffness and greatly reduce the service life of materials.Therefore,the evaluation of fatigue damage properties of composite materials has become a hot research topic.Firstly,the domestic and foreign research status of fatigue life prediction method is introduced and mainly the residual strength model,the residual stiffness model and fatigue modulus model are analyzed in the paper.Based on these analysis and discussion,the evolution law of fatigue damage accumulation of composite materials to predict the structural fatigue life of composite materials is used.Fatigue damage cannot be measured directly,so the elastic modulus of composite material is used to quantitatively evaluate it.Secondly,based on the evolution mechanism of fatigue damage of composite laminates,the fatigue residual stiffness degradation model,considering many influencing factors,is proposed and applied to predict the fatigue life of composite laminates.The model considers the mechanical properties of the component material,fiber ply angle,interface strength and volume fraction of fiber.The fatigue life prediction of laminated plates mainly includes three dimensional model establishment,fatigue failure determination and material property degradation.The laminates with defect holes are selected as the research object and the finite element software is used to analyze stress;The improved Hashin failure criterion is introduced to determine the failure modes;the mechanical property degradation of the complete failure unit and the quasi failure unit are performed respectively by using the unit drop degradation model and the progressive degradation model.Finally,the tensile strength of the T300/YPH-209 laminates is obtained by static tensile test.Then,the tensile fatigue test of the laminates under different stress levels is carried out;the fatigue life of material can be obtained,and the S-N curve is drawn.The residual stiffness of laminates is monitored in real time,and the residual stiffness values under different cycles are plotted to obtain the influence of the stress level on the residual stiffness.The feasibility of the model is verified by comparing the experimental values with the predicted values of the model.