Study On Mechanism Of Interfacial Crack Growth In Laminated Structure Of Carbon Fiber Composite

Carbon fiber reinforced epoxy resin matrix composite is typical material of light weight and high strength with superior performance and extensive application.It is a unremitting pursue goal of researchers to enhance its fracture strength and prolong its service life,and interlaminar stress has a crucial influence on its mechanical properties.For gaining the influences of the relatived factor on interfacial crack growth in laminated structure of carbon fiber composite,its fracture mechanism was investigated systematically with numerical simulation and experimental method.The specific tasks of study are as follows:1.In consideration of the anisotropy of material and the uncontinuity of interface,on the basis of extended finite element method,the crack is regarded as discontinuous geometry,and the interval discontinuous function is taken as a part of interpolation functions.Cohesive interface elements were constructed by combining cohesive zone model.On this basis,numerical model of interfacial mode I crack growth in laminated structure of carbon fiber composite was established.The crack growth process was simulated by using interface elements,and fracture parameters were calculated by applying virtual crack closure technique.The fracture criterion of critical energy release rate was adopted for finite element analysis of interfacial crack growth in laminated structure of carbon fiber composite.2.Tensile tests of laminated structure specimen of carbon fiber composite with initial crack were carried out by means of electronic universal material testing machine,and interfacial mode I crack growth at different geometrical dimensions and ply angles were studied.In quasistatic loading,mode I crack grows linearly and tends to grows crookedly along the interlayer interface.Compared with numerical simulation results,it is proved that the model is in accordance with the actual crack growth process,and correctness of the model is verified.3.On the basis of the model,the quantitative studies on the influence factors of interfacial crack growth in laminated structure of carbon fiber composite were carried out.The results showed that alongwith the increase of elastic modulus of carbon fiber,interfacial cohesion increases therewith,energy release rate decreases,and crack is gradually difficult to grow.Crack growth is relieved by changing elastic modulus ratio of carbon fiber and epoxy resin.The increase of initial crack length can amplifies stress concentration at the crack tip and increases energy release rate evidently,therefore crack is easy to grow.The thickness and width of the material have great influence on crack growth.The smaller the width of thematerial,the easier the crack grows.In virtue of the effect of shear stress within the structure,crack growth is from easy to difficult alongwith the increase of the thickness of the material.The length of the material has little influence on crack growth.In the case of different ply angles of carbon fiber,crack-resistance of cross-ply laminated structure is better than that of angle-ply,and number of plies of carbon fiber almost has no influence on crack growth.4.The results can provide a reference to fracture study of laminated structure of carbon fiber composite.The laminated structure design of carbon fiber composite can be improved by using its designability and the influences of the relatived factor,and then its fracture strength is enhanced.