Design,Simulation and Experimental Study on Electromagnetic Shielding Structure of Carbon Fiber Reinforced Composites for Railway Vehicles
Supervisor:sun shou guang
In order to meet the lightweight requirements of rail vehicles,this paper carries out the simulation design and forming process research of carbon fiber composites(CFCs)for frequency conversion box to satisfy the electromagnetic compatibility.By overcoming the low frequency electromagnetic protection technology,the engineering application of CFCs in the field of rail vehicles is promoted.The mechanical properties of existing carbon fiber composites meet the requirements of railway vehicles,but its electromagnetic shielding(EMS)is poor,so it is necessary to improve its low-frequency protection performance.By analyzing the characteristics of electromagnetic interference in railway vehicles,the integrated protection principle of EMS for CFCs is proposed and its laying structure is designed.By magnetic nanoparticles surface modification of CFCs and technology optimization of autoclave forming,CFCs with broadband high-efficiency electromagnetic is produced to satisfy the requirements of railway vehicles.Then,a broadband high-efficiency EMS coating was obtained by simulation optimization and experiments for its application in railway vehicles.The main research works are as follows.(1)The mechanical and shielding effectiveness(SE)properties of existing CFCs were firstly studied.The results show that CFCs have good mechanical properties,some of which are better than that of aluminium alloy sheets(6082),but the low-frequency ES of CFCs is poor.It is necessary to modify CFs and optimize the laying design to improve its low-frequency SE to meet the requirements of the electromagnetic protection in railway vehicles.(2)Based on the analysis of the electromagnetic interference characteristics in railway vehicles and the design principles of electromagnetic protection,the ES index of CFCs is put forward and the scheme to improve its the low-frequency protection performance is designed.The results show that the low-frequency(<100kHz)magnetic field in railway vehicles is more harmful,so it is necessary to improve the low-frequency EMS of CFCs to ensure the electromagnetic compatibility of railway vehicles.The design of multi-layer shielding materials can achieve broadband protection effectiveness.Low permeability and unsaturated materials are firstly used to reduce the magnetic field strength,then high permeability materials are used for EMS.Finally,carbon fiber composite materials with different layers are designed to satisfy the requirements of low-frequency electromagnetic protection for rail vehicles(3)Two EMS structure of Co3O4/CF and Co3O4/Fe2O3@CF were successfully prepared by hydrothermal method and pyrolysis method.The good magnetism of Co3O4 in Co3O4/CF fully guarantees its EMS performance,while the loose coating can reduce the density of the composites.At the same time,the nano-Co3O4 fiber coating will help to improve the interfacial strength between the fibers and resins in the CFCs;the magnetic Co3O4/Fe2O3 nanowires are prepared on CFs,then the loose nanoparticles will help to reduce the density of the composites and nano-line magnetic grains are helpful to improve the interfacial bond between CFs and resins.(4)In this part,the effects of autoclave forming parameters(temperature and pressure)on the mechanical properties of CFCs were studied.The results show that there are white areas in the composite,which is the segregation area caused by the poor fluidity of the resin.Increasing the forming temperature or pressure,the fluidity of the resin is improved and makes the infiltration of the resin and CFs more fully,reducing the number and area of the resin segregation area in the CFCs.The tensile strength,bending strength and impact strength also increase with the forming temperature or pressure.Finally,the optimum forming parameters of autoclave are at 150℃ with a pressure of 0.5 MPa.(5)The mechanical and shielding properties of the designed electromagnetic shielding integrated CFCs were studied,and the simulation and test results of the shielding effectiveness(SE)of CFCs with different layers structure were obtained.Compared with the shielding effectiveness of pure CFCs,the EMS of CFCs at low frequencies was improved.Increasing the layer numbers of magnetic particles CF or permalloy can further improve the EMS of CFCs and meet the requirements in rail vehicles.CFs with magnetic particles or permalloy can weaken or hinder the flow of resin,which cause the segregation tendency of the resin and destroy the continuity and integrity of the material.Finally,the mechanical properties,electrical conductivity and magnetic conductivity of the CFCs are reduced.The measured SE is lower than that of theoretical values,but the trend of change is consistent with the calculation results.(6)A new broadband EMS coating material system for CFCs was simulated and designed by numerical simulation.The effects of conductivity,permeability and thickness on SE of coatings at low,medium and high frequencies were obtained.A coating with broadband and high EMS was prepared.The measured SE data of the coating material were similar to the simulation results,and the error was±4dB.In order to improve the low-frequency protection performance,the low-frequency protection CFCs were designed and developed based on the theory of electromagnetic protection.Finally,by the combination of simulation and experiment,CFCs with low-frequency protection is designed and developed through the process parameters and laying design to meet the lightweight requirements of railway vehicles.