Strengthening Mechanism Of Carbon Fiber Composite Reinforced By Short Aramid-fiber

Carbon fiber composites are widely used in the aerospace and automotive industries due to their high specific strength and stiffness.The carbon fiber laminated composites are multi-layer carbon fiber composite structure based on resin matrix,in which there are multi-layer adhesive layers and adhesive interfaces.Because of the brittle of the resin matrix,the strength and fracture toughness of the interface between carbon fiber and resin matrix is poor,which become the key factor affecting the overall mechanical properties of the composites.To solve this problem,the Kevlar fibers(aramid fibers)were used to reinforce the adhesive layers and the interfaces.Based on the double cantilever beam(DCB)test,the reinforcement mechanism of the Kevlar fiber to the carbon fiber composites was studied.The main research contents include:(1)First,the pure resin matrix of the adhesive layer was reinforced with Kevlar fiber film to form the composite adhesive layer with Kevlar fiber as the skeleton.Compared with the pure resin structure,Kevlar fiber film can make the ultimate bearing capacity of the adhesive layer and the fracture toughness increased by 75%and 103.9%,respectively,and can coordinately enhance the strength of carbon fiber/resin interface,prevent the cracks from expanding along the carbon fiber/resin interface and the interface from delamination.(2)In order to reduce the interface defects between Kevlar fiber and resin matrix,improve the interface strength,the surface pretreatment technology was used to treat the surface of the Kevlar fibers,to improve the wettability of the resin to the Kevlar fiber film,increasing the pull-out resistance of the Kevlar fibers.After surface pretreatment,the ultimate bearing capacity and the fracture toughness of the adhesive layer were further increased by26.97%and 27.60%,respectively.Then microscopical analysis to the reinforcement mechanism with Kevlar fiber was performed using metallographic microscopy and SEM.(3)Because of the small size of the adhesive layer,different lengths of Kevlar fibers can affect the arrangement and reinforcement mechanism of the fibers in the adhesive layer.In view of this situation,the effect of four lengths of Kevlar fiber on the adhesive layer was studied.The results showed that different lengths of Kevlar fibers have different bridging in the adhesive layer.In the range of 3 mm to 12 mm in length,the shorter the Kevlar fiber,the easier the two free ends of the fiber synergistically form strong bridging.The longer the Kevlar fiber,the easier it is to debonding,causing the weaker bridging.(4)In order to study the influence of the number of Kevlar fibers on the strength of the adhesive layer,Kevlar fibers with a length of 3mm were used as the object.Three different density Kevlar fiber films were studied.The results showed that,in the range of 12g/m~2 to36g/m~2,the greater the density of Kevlar fiber film,the more effective Kevlar fibers in the adhesive layer participating in bridging.