Investigation Of Regulation Mechanism Of Axial Compression Fracture Mode For Covered Fiber Composite

Carbon fiber composites have the characteristics of high strength,high stiffness and light weight,which have the prospect of wide application in aerospace and other fields.In recent years,due to the low compression and tension of carbon fiber resin matrix composites,it seriously limits the application on the main load-bearing structural members,which affects the safety and reliability of the composites in the process of use.It is of great significance to carry out research on the axial compression fracture mode of fiber-reinforced composites and its performance enhancement,to further optimize the structure of fiberreinforced composites and to improve the action efficiency of the composite structural system,in order to improve the compression strength of composites in a reasonable and efficient way.In this paper,imitating the winding bionic structure of nature,we design a kind of covered structure fiber-reinforced composites,use filament winding method to wrap carbon fiber bundles,prepare columnar carbon fiber composites with different covered parameters,study the axial compression performance of the composites,make microscopic observation on the cracking and extension pattern of the material,and explore the correspondence between the fiber covered parameters and the diameter of the composites and the fracture mode in axial compression.The connection between carbon fiber buckling instability and fiber kinking in axial compression damage,optimize the structural design of clad fiber reinforced composites,and provide theoretical basis and experimental foundation for the preparation of composites with high compression properties.The study mainly includes.(1)Study of the covered fiber density on the axial compression mechanical properties and failure mechanism of composites.When the covered density was 45 r/10 cm,the axial compressive strength of the composite reached the maximum of 236.46 MPa,which was 180% higher than that of the unclad specimen.The increase was 158.1% at a covered density of 35 r/10 cm and 40 % at a covered density of 15 r/10 cm.The fiber covered can reduce the flexural wavelength of the fibers during the compression process,thus improving the compression properties of the composite.Moreover,the higher the covered density,the smaller the flexural wavelength of the fibers in the composite material when compressed,the higher the critical compression load,the higher the critical compression load that can be withstood,and the better the compression performance.(2)Study on the mechanical properties and failure mechanism of composite materials in axial compression by the type of covered fiber.The research results show that due to the low strength of UHMWPE fibers,there is an obvious fracture situation,so in terms of modulus,when the diameter of the composite is raised from 3 mm to 4 mm,the modulus decreases significantly and there is a fracture-type decrease,with a maximum decrease of 72.6 %.When the composite is subjected to axial compression force,the carbon fibers are axially stressed and flexure occurs,and the carbon fibers are laterally supported by the resin matrix,and the modulus of the covered fibers has a greater effect on the axial compression of the composite.The covered fiber will inhibit the carbon fiber from buckling,so that the carbon fiber always remains in the axial direction when subjected to compression load,limiting its buckling state,thus improving its compression strength,but when the strength of the covered filament is low,the axial compression process cannot effectively block the transverse strain caused by pressure,thus making cracks and shear between resin and fiber or resin.(3)Study of the clad fiber diameter on the axial compression mechanical properties and failure mechanism of composites.The results show that the compression modulus reaches a maximum of 16 MPa at a covered fiber diameter of 0.1 mm,after which the compression modulus decreases with decreasing covered fiber diameter,and decreases by62.5% at a covered fiber diameter of 0.6 mm.As the diameter of covered fiber decreases,the compressive properties of the composites will gradually improve,and the fiber covered changes the fracture mode of the material during compression damage,so that the damage form of carbon fiber becomes torsional damage,similar to shear damage.However,the fiber covered will reduce the tensile strength of the composite.(4)Study on the diameter of composites on the axial compression mechanical properties and failure mechanism of composites.When the diameter is 4 mm,the fiber volume fraction is the lowest and the failure form of the composite is mainly plastic destabilization damage;when the diameter is 3 mm,the fiber volume fraction is higher,the vertical stability of the fiber is improved,and the interfacial bonding performance is improved,so that the stress transfer between the fiber and resin is more effective.The compression failure form is dominated by fiber fracture and fiber kink band.The higher the volume fraction of fibers,the tighter the fiber stacking,which can effectively prevent the microflexion phenomenon of the composite.