Design And Performance Characterization Of Composite Structures Based On The Buckypaper For Lightning Strike Protection

The buckypaper?BP?called ‘carbon nanotube film' which is a macroscopic material of carbon nanotubes?CNTs?,has light weight,corrosion resistance,execellent electrical conductivity and other advantages.In addition,the BP also has the easy maneuverability and can easily prepare resin matrix composite,which the CNT powders do not possess.Therefore,the BP and its composites are obtained from more researchers' attention in recent years.According to reports,the BP and its composites have huge potential applications in the lightning strike protection?LSP?for the aircrafr,owing to their excellent properties.In this thesis,various types of modified BPs and their composites were prepared and researched for enhancing the lightning strike protection preformance of protective structures based on BP materials.According to the optimal design,a series of lightning strike protection composites based on BP materials were prepared and verified possibility of these composites applied in the lightning strike protection field.Random BPs that were used in this thesis were mainly prepared via the CNT suspension filtration method.After removing residual surfactants,electrical conductivity of the BP was increased slightly and its EMI shielding effectiveness values ranged from 34.3 d B to 42.9 d B in the Ku band?12-18 GHz?.For enhancing mechanical property of the BP,carbon nanotube/polyacrylonitrile?CNT/PAN?composite films were prepared through introducing PAN electrospinning fibers and their mechanical properties were enhanced slightly.The PAN layer permeated CNT powders contained massive interfaces that can consume electromagnetic wave.The EMI shielding effectiveness values of CNT/PAN composite in the Ku band ranged from 63.7 d B to 65 d B.However,its conducitivity reduced slightly,which can not meet the damand of the LSP material.For improving the conductivity,cross-linked BPs?CL-BP?were fabricated through chemical cross-linking method.Both conductivity and mechanical preformance of the as-prepared CL-BP were effectively enhanced,whereas its resin compatibility was poor.It is not suitable as the LSP structure for the carbon fiber reinforced polymer?CFRP?matrix composite.To further enhance the conductivity of the BP and satisfy the need of highly conductive material for the LSP.Based on the design,a side of the BP was modified by silver particles via the electrophoretic deposition?EPD?method.The silver modified buckypaper?SMBP?with high conductivityity was acquired and its electrical conductivity increased to 5091.65 S/cm.In addtion,the SMBP contained a small content of silver particles and kept lightweight.The SMBP also possessed the porous structure and the resin can easily spread on the SMBP surface.Thus,the good compatibility between SMBP and resin is beneficial to the SMBP as a LSP functional layer of CFRP materials which are usually applied in the aviation industry.The composite has potential application in the LSP field,owing to its high conductivity,light weight,corrosion resistance,stable structure and other advantages.The results showed that the compressive strength retention rate of the SMBP/CFRP composite after the lightning striking?LS?was 90.75%,and it was much higher than that of the CFRP composite without any protective layer after the LS?60.45%?.Moreover,the LSP effect of the SMBP/CFRP composite was similar to the CFRP composite protected by the commercial LSP copper mesh with an areal density of 73 g/m²?73gsm-Cu?.However,the weight of the SMBP as the LSP layer reduced 27.4% than the 73gsm-Cu.Moreiver,the maximum temperature variation of the non LS side of the SMBP/CFRP composite panel reduced 17.4 ? during the LS compared with the 73gsm-Cu/CFRP composite.In this thesis,the conductive protection mechanism of the SMBP was analyzed by the Raman spectrum,XRD,XPS and other characterization methods.Based on the conductive protection of the SMBP,this thesis provided a novel LSP method for the CFRP composite from the thermal protection,which was adding highly conductive SMBP and carbon fiber/phenol formaldehyde resin?CF/PF?protective layer as the composite LSP structure on the composite surface.The synergistic effect of SMBP and CF/PF protective layers can reduce the damage caused by the LS energy.The compressive strength retention rate of the SMBP-CF/PF-CFRP composite after the LS was 97.25%,and it was slightly higher than the CFRP composite protected by the commercial copper mesh with an areal density of 142 g/m²?142gsm-Cu,96.1%?.During the LS process,the maximum differential temperature of non LS side of the SMBP-CF/PF-CFRP composite panel was 44.9 ? that was lower than that of the 142gsm-Cu/CFRP composite?51.1 ??.The possible LSP mechanism of the CF/PF as the dissipating LSP layer was researched by the simulation.The results indicated that the damage of the CFRP matrix caused by the LS can be reduced by introduction of the CF/PF layer.Based on the SMBP-CF/PF composite LSP structure,added the aluminium oxide?Al₂O₃?powders as the thermal-protective layer into the composite through the optimum structural design,which can prevent Joule heat from conducting into the CFRP matrix,for further reducing the damage caused by the LS energy.The SMBPCF/PF-Al₂O₃-CFRP and SMBP-CF/PF-Al₂O₃/PI-CFRP composites were prepared via the vacuumed hot-pressing method.The LSP performance of above two composites were verified.The results illustrated that the compressive strength retention rate of the SMBP-CF/PF-Al₂O₃-CFRP composite after the LS test was the highest,which was 98.92%.The SMBP-CF/PF-Al₂O₃/PI-CFRP composite displayed the best heatprotective effect of all the CFRP matrix composites,and its maximum temperature variation of non LS side was only 23.6 ? during the LS test.The possible LSP mechanism of the CF/PF-Al₂O₃ composite structure was researched.The simulated results illustrated the damage of the CFRP matrix caused by the LS can be obviously reduced,due to introduction of the Al₂O₃ layer.In term of the weak status of the researches on BP composite structures for the LSP application,related fabrication strategies of the BP composite structures with the conductive and thermal protective layers were studied in this thesis.According to the characterization and analysis of morphology and related properties,the possible LSP mechanism of LSP composite structure based on the BP was investigated.Results and conclusions that are obatained from this thesis,will provide an idea for future research on lightweight composite materials for the LSP field.