Numerical Simulation And Experimental Study On Crack Propagation In Carbon Fiber/Epoxy Composite

Carbon fiber reinforced resin matrix composites are widely used in machineryequipment, aerospace and marine engineering due to its high specific strength, highspecific modulus and outstanding designability. But in recent years the compositesfracture problems have become increasingly prominent, seriously affecting the safeuse of composite material components. Therefore it is of great importance to studycrack propagation in composite material structures.In this paper, as the basic unit of composite material, a single cell model wasestablished. The Extended Finite Element Method(XFEM) was introduced to studythe effects of fiber volume content, fiber/matrix interfacial strength and fiberarrangement on crack propagation in a microscopic perspective, from whichcharacteristics of crack propagation in micro scale was obtained. The results showedthat low fiber volume fraction and a strong interface may contribute to composites'resistance to crack propagation. But considering the material stiffness, a very lowfiber volume fraction is not favourable. In this paper, fiber volume fraction of40%is more reasonable. Furthermore, uneven fiber arrangement led the micro crack tomerge into the main crack more easily, thus affacting the crack propagation path.Cohesive element model was established to simulate interlaminate crackpropagation and XFEM was employed to simulate inner layer crack propagation, allof which provide information and reference for the study of crack extension incomposite structures.The numerical simulation results showed that ply angleselection and volume fraction of plies with differente angles, has a great impact oncrack propagation. Small angle ply has an important impact on the limite load forinitial crack propagation in composite laminates. The more small angle plies, thelarger the interlaminar tensile limit load would be, as well as the failure load of firstdamaged unidirectional ply in a laminate structure under tensile loads.Hydrostatic pressure testing was conducted to determine the threshold load ofcrack propagation. It was shown that the threshold load of the specimens preparedfor the hydrostatic pressure testing was10MPa. However, when a pressure largerthan10MPa was loaded, the laminate still remains a certain carrying capacity. In theexperiment, the crack propagation direction is perpendicular to the fiber direction,which is also displayed by numerical simulation results. The consistency of crackpropagation characteristics in experiments and simulation proved the validity ofnumerical simulation method.