Study On The Structure And Properties Of Carbon Fiber Unidirectionaland Three-Dimentional Woven Hybrid Fabric Infusion Molding Composites

Carbon Fiber Reinforced Polymer(CFRP)is widely used in aviation,aerospace and rail transit due to its high specific strength and modulus,good fatigue resistance and strong designability.In CFRP,carbon fiber three-dimensional woven composites prepared by resin perfusion molding have the advantages of high impact damage tolerance,high specific energy absorption and easy to form complex structural parts,which have been developed rapidly in recent years.However,for three-dimensional braided CFRP,due to its weaving process and fiber orientation,the mechanical properties of the composites along the braided direction are lower than those of the unidirectional composites at the same volume fraction,which cannot meet the engineering needs of some specific fields.In this regard,some researchers introduced axial yarns in the weaving process to enhance the bearing capacity of composites by increasing the fiber content in the axial direction,but this way has limited improvement in the axial mechanical properties.Therefore,it is of great significance for the application of 3D braided CFRP to study how to improve the axial mechanical properties of 3D braided composites and maintain their overall mechanical properties.In this study,the composite side beam of the bogie frame of a high-speed rail train was taken as the research background.The unidirectional carbon fiber fabric and the three-dimensional braided fabric were used for interlaminar hybrid,and the three-dimensional braided / unidirectional carbon fiber fabric(3D / UD)hybrid CFRP laminates with excellent in-plane and interlaminar properties were prepared by the perfusion molding of epoxy resin.The structure and mechanical properties of the hybrid CFRP laminates were further studied,and the failure mode and energy absorption characteristics of the hybrid CFRP tubular structure under crushing were further analyzed.The research contents and results are as follows :(1)The carbon fiber three-dimensional braided fabric was prepared by four-step rotary knitting process,and the hybrid layer of carbon fiber unidirectional fabric and three-dimensional braided fabric was used.The CFRP laminates were prepared by vacuum assisted perfusion molding process.The effects of different hybrid ratios of carbon fiber three-dimensional braided / unidirectional fabric,different stacking sequences and different stacking angles on the structure and properties of carbon fiber three-dimensional braided / unidirectional fabric reinforced epoxy resin matrix composites were systematically studied.The results show that the mechanical properties of CFRP are greatly affected by the orientation of carbon fiber,the hybrid ratio of three-dimensional braided carbon fiber / unidirectional fabric and the stacking sequence.The tensile and compressive properties of CFRP increase with the increase of 0° carbon fiber unidirectional fabric;the storage modulus and flexural properties first increase and then decrease with the increase of 0° carbon fiber unidirectional fabric;under the same carbon fiber three-dimensional braided / unidirectional fabric hybrid ratio,different stacking sequences have great influence on the bending performance.When the unidirectional carbon fiber fabric is uniformly dispersed among the three-dimensional braided fabrics,the interlayer shear performance of CFRP is the best.Adding three-dimensional braided layer in unidirectional carbon fiber fabric can effectively improve the low-speed impact resistance of CFRP,and adding unidirectional carbon fiber fabric in braided layer can effectively improve the compressive strength after impact.(2)The square tubular CFRP structural components with different hybrid ratios and stacking sequences that are proportionally reduced to the diameter size of the bogie side beam are prepared by vacuum assisted resin transfer molding process.The quasi-static axial compression test is carried out to study the failure mode and energy absorption characteristics.The results show that each hybrid specimen presents progressive damage failure when crushing;when the hybrid ratio of carbon fiber three-dimensional braided fabric and carbon fiber unidirectional fabric is different,with the increase of three-dimensional braided layer,the average compression load of CFRP square tube increases in the post-compression stage,maintains at a high level,and the average specific energy absorption increases gradually.When the hybrid ratio of three-dimensional braided carbon fiber / unidirectional fabric is the same,the three-dimensional braided layer is beneficial to improve the energy absorption level of tubular CFRP at the outermost layer.(3)In order to study the energy absorption characteristics of bogie side beam more efficiently,the finite element model of 3D / UD hybrid CFRP square tube was established by ABAQUS software,and the 3D-Hashin criterion was used as the failure criterion to simulate the crushing process of quasi-static axial compression of hybrid CFRP square tube.The simulation results of hybrid CFRP square tube failure process and energy absorption characteristic parameters are in good agreement with the test results,which verifies the validity of the model.