Mechanical, Interface And Fatigue Resistance Of Carbon Fiber Reinforced Epoxy Composites Based On Carbon Nanotubes

With the application of carbon fiber(CF)reinforced epoxy(EP)composites in many fields such as aerospace,wind power,sports equipment and so on,people have put forward higher requirements for the performance of composites.Therefore,the study of composite modification is particularly important.Carbon fiber reinforced epoxy composites are three-phase structures,including reinforcement(carbon fiber),matrix(epoxy)and interface,so the performance of composites is also determined by the properties of carbon fiber,matrix and interface.Due to the unique structure and excellent properties of carbon nanotubes(CNTs),CNTs have been widely used to improve the properties of composites.The modification of CNTs is generally based on matrix modification or interface modification,but there are few reports on the comparison and research of interface modification and matrix modification,systematically.In this study,CNTs were introduced into the composites by electrophoretic deposition and ultrasonic blending,respectively.The mechanical,thermal,interface,fatigue properties of the two modified composites and the effect of CNTs on properties of composites were studied and compared.Single-fiber fragmentation test combined with energy dispersive X-ray spectroscopy was creatively applied to calculate interfacial shear strength and improvements of 10.14%and 45.2%were achieved for composites based on CNT-reinforced matrix(CF/EP-CNTs)and hierarchical composites based on CNT-modified fibers(CF-CNTs/EP),respectively.The tensile strengths of CF/EP-CNTs and CF-CNTs/EP composites were increased by 10.41%and 24.42%,respectively.The residual flexural strength retention ratio of CF-CNTs/EP increased by 3.84%after 30,0000 times of fatigue damage in tensile-pull mode,and the residual flexural strength retention of CF/EP-CNTs increased by 1.21%after the same number of fatigue loading.In addition,CF-CNTs/EP was found to have less internal fatigue damage than CF/EP-CNTs by ultrasonic C-scan.The effects of CNTs on the properties of the composites and the interface structures were analyzed and characterized.were investigated by means of elemental analysis(EDX),atomic force microscopy(f-AFM)and transmission electron microscopy(TEM),respectively.It was found that in CF-CNTs/EP,part of the CNTs can diffuse into the resin matrix around the carbon fibers during molding and curing of the composite,which can make the matrix tough and form a gradient interface layer that can significantly reduce the stress concentration.For CF/EP-CNTs,CNTs blended with the resin only toughened the resin matrix,and did not form a gradient interface layer.The interfacial modification can improve the mechanical properties,:interfacial properties and fatigue resistance of the composites obviously,which can meet the demands of carbon fiber reinforced epoxy composites.Therefore,interfacial modification has more advantages than matrix modification in fiber reinforced composites.