Analysis Of Compression Behavior Of Carbon Fiber And Its Composite

Carbon fiber and its composites have been widely used in the military and civilian fields.However,compared with the tensile strength,the compressive strength of carbon fiber is relatively low,which has limited the further development and application.Therefore,it is important to improve the compressive strength of carbon fiber.It was shown that the compressive strength of carbon fiber plays a decisive role in the compressive strength of composite materials in previous studies.The microstructure of carbon fiber determines its compression performance,and the modulus and diameter of carbon fiber also affect the compressive strength of composite materials.However,the main problem is that the test methods for the compressive strength of carbon fiber are limited,and the results obtained by different test methods are incomparability.In this study,in order to avoid the limitations of experimental tests and control single variables,ABAQUS was used for simulation and exploration.Firstly,based on the theoretical basis of the two-dimensional Hashin progressive criterion,the compression behavior of unidirectional carbon fiber reinforced resin matrix was simulated,and the different loading between the carbon fiber and the resin matrix under compressive load were interpreted.And the difference of the roles between the carbon fiber and the resin matrix under compressive load were also studied.Secondly,the carbon fiber monofilament itself was taken as the research subject.Then the compression behavior and tensile behavior of the monofilament were simulated respectively to explore the reasons why the compression strength of carbon fiber is lower than the tensile strength.Finally,the influence of Young's modulus,diameter,microcrystalline size and the difference of modulus between skin and core on the compressive strength of carbon fiber was investigated.The results indicated that:(1)It was found that carbon fiber plays a decisive role in the compression behavior of composite laminates by two-dimensional Hashin progressive model.Therefore,to explore the compression behavior of composite materials,it is necessary to analyze the compression behavior of carbon fiber monofilaments.(2)Carbon fiber monofilaments have different stress-bearing conditions when they are subjected to tension and compression.When the single-filament carbon fiber is subjected to tensile force,tensile deformation occurs and fracture occurs in the middle section.While under compression,micro-buckling deformation occurs,which is the main reason that causes the carbon fiber compressive strength to be lower than the tensile strength.The occurrence of buckling cancels out with the force that should be increased,resulting in less stress that can be borne.It is shown that the work done by the external force of pulling carbon fiber is much larger than that of crushing.(3)When the diameter of carbon fiber is large,the degree of micro-buckling is small,the compressive strength and the ratio of compressive-tensile strength is large when the carbon fiber is subjected to compression load.The increase of diameter can increase the radial length of the bearing surface and alleviate the micro-buckling deformation.When the Young's modulus is large,the micro-buckling occurs in order to maintain its original shape under load.As a result,the compressive strength is small(4)With the increase of axial mesh size,the degree of micro-buckling decreases,and the compression strength and the ratio of compressive-tensile strength increase.The compression strength and compression strength ratio of carbon fiber can be increased by appropriately increasing La.Secondly,with the increase of radial mesh,the degree of micro-buckling increases,the compression strength and the ratio of compressive-tensile strength decreases.The compression strength and compression strength ratio of carbon fiber can be increased by reducing Lc appropriately(5)The homogeneous carbon fiber has lower micro-buckling and higher compression strength than the inhomogeneous carbon fiber.The more the inhomogeneous,the lower the compression strength.The weakened skin-core structure can increase the compressive strength.