Study On Tensile-Tensile Fatigue Damage Characteristics Of Carbon Fiber Reforced Composites

As an advanced material with high specific strength and high specific stiffness,fiber reinforced composites have been vigorously developed and widely used in the21 st century,especially in some fields such as aeronautics and astronautics,wind-power blades,automotive light weighting,building reinforcement,the utilization rate of carbon fiber composite is rising greatly,and is seem to be a good substitute for part of the metal.However,in some complicated situation,this kind of fiber composite material still faces some problems of fatigue failure and structural damage,which restricts the popularization and application of fiber reinforced materials.Therefore,the study of fatigue failure characteristics and fatigue performance of fiber reinforced composites is helpful to deepen the understanding of this material and expand the performance advantages of this material.In addition,the research on the fatigue life prediction of composite materials is also helpful to establish the fatigue life prediction system of composite materials,avoid some accidental property damage and personal injury.In this paper,the research is based on the composite material,with the reinforcement phase of carbon fiber,and the matrix of epoxy resin.The work of this paper focus on the fatigue failure characteristics,the fatigue performance and the prediction of fatigue life of the fiber reinforced composite.There are specific aspects of the work and results as the following.(1)In this paper,the quasi-static tensile test and tensile-tensile fatigue test of carbon fiber reinforced epoxy resin matrix composites were firstly carried out to test the tensile strength and fatigue life of the material under different load levels.The fatigue failure morphology of the samples was analyzed to obtain the fatigue failure characteristics.It is found that the main damage forms and speed of damage development are different as fatigue cycle increases,and the change shows three stages.(2)Based on the results of tensile test and tensile-tensile fatigue test,the fatigue damage criterion,the residual strength model and the residual stiffness model,the fatigue life model and the material performance sudden decline method are determined.By using the UMAT subroutine of ABAQUS,the fatigue simulation of composite materials was carried out to simulate the generation and propagation process of fatigue damage,as well as the degradation process of strength and stiffness,and the fatigue life of composite materials is predicted.Simulation prediction was verified by the experiment results.(3)The quasi-static tensile strength and tensile-tensile fatigue life of epoxy resin composites prepared with different matrixes which are modified with micron alumina ceramic particles and multi-walled carbon nanotubes are tested.The results show that the tensile strength of the composite modified with micron alumina ceramic particles is higher than that of unmodified composite,but its fatigue property is inferior to that of unmodified composite.The microscopic images show that the adhesion between alumina particles and matrix and the adhesion between alumina particles and fiber are both poor.The dispersed particles weaken the damage capacity of matrix,accelerate the debonding of matrix and fiber and the propagation of crack.However,the performance of the material modified with multi-walled carbon nanotubes is different.Although the tensile strength of the modified material is less and the material fails faster at high level load,the fatigue performance of the modified material is much better than that of the unmodified material at lower level load.Comparing morphology of this two materials,matrix modified with multi-walled carbon nanotubes have a stronger binding force with fiber,which delayed the generation and propagation of interface cracks.And with a larger specific surface area the multi-walled carbon nanotubes can block the connection and the development of micro cracks,consume part of energy,reduce the stress field energy in the front of crack,so that the time of material failure is delayed,material life is improved.