| PTFE/Kevlar hybrid fabric self-lubricating composite is a new type of self-lubricating material,which is composed of PTFE fiber with low friction coefficient and Kevlar fiber with good mechanical properties,using epoxy resin as the matrix.It is widely used in the aerospace,automotive and heavy machinery industries as a lubrication liner between the inner and outer rings of spherical plain bearings due to their excellent properties as self-lubricating,low friction coefficients,strong mechanical properties,lightweight,good corrosion resistance and so on.PTFE/Kevlar hybrid fabric composite is continuous fiber reinforced composites,the physical adhesion between fabrics and polymer matrix plays an important role in its extraordinary mechanical and adhesive performances,which are mainly controlled by the wettability of the fabrics.And in the practical application of joint bearing,PTFE/Kevlar hybrid fabric bonding surface and friction surface need to undertake different work content:bonding surface to ensure bonding strength,should maintain good wettability with resin matrix;The friction surface should avoid immersion resin,affect the antifriction effect,need to maintain good non-viscosity.Therefore,the mesoscopic wettability model of PTFE/Kevlar hybrid fabric was established in this paper.Based on the hierarchical wettability of the fabric,the PTFE/Kevlar hybrid fabric was designed and modified.The wettability between the friction face and adhesive face of the fabric with resin matrix were studied,and the interfacial properties,friction and wear resistance of the fabric composite were discussed.Based on the Cassie-Baxter and Wenzel model,a three-phases Cassie-Baxter-Wenzel wetting model was established.The fabric structure and fiber content of PTFE/Kevlar hybrid fabric were designed and screened according to the predicted contact angle,and then the PTFE/Kevlar fiber fabric was woven by automatic rapier loom.Based on the actual fabric structure of PTFE/Kevlar fabric,the geometric model of PTFE/Kevlar hybrid fabric was constructed.The wetting behavior between PTFE/Kevlar fabric and deionized water was studied in stages,and the theoreti cal relationship between the contact angles of single fiber,fiber tow and fabric was revealed.The wettability of PTFE/Kevlar hybrid fabric and epoxy resin was predicted by the mesoscopic wetting model based on contact angle between single fiber and liquid epoxy resin.The predicted contact angle between the adhesive face and liquid epoxy resin is 79.88°,which indicates that the fabric composition and content design cannot meet the wettability requirements.The KrF laser single-side modification method is proposed.Through the KrF excimer laser single modification on the PTFE/Kevlar hybrid fabric,the wettability between the adhesive face and epoxy matrix improved,and the friction face is not affected by modification,keep the non-stick performance.The modification mechanism of KrF excimer laser was studied.The surface roughness and surface morphology of PTFE and Kevlar fibers were observed and analyzed by SEM,AFM and LCSM.The surface energy of PTFE fiber and Kevlar fiber was calculated by Owens second liquid method and Lewis acid-base method,respectively.Moreover,single filament tensile test was used to verify that the treatment has no effect on the mechanical properties of Kevlar fiber.The influence of KrF laser on the wettability of PTFE fiber,Kevlar fiber and PTFE/Kevlar fabric with epoxy resin was studied by measuring the dynamic contact angles between PTFE and Kevlar fiber and liquid resin,and observing the wetting behavior of epoxy resin droplets on the fabric surface.PTFE/Kevlar hybrid fabric was bonded and solidified on the metal matrix by epoxy resin,and PTFE/Kevlar fiber fabric composite was prepared.The peeling test showed that:after treatment,the bonding property between fabric and metal matrix has been effectively improved.The friction and wear behavior of PTFE/Kevlar fabric composite was studied by the friction and wear tests under different speeds and loads.The friction coefficient represents the friction behavior of the fabric composite:the friction coefficient increases with the increase of the speed,and gradually decreases with the increase of the load,and finally reaches a constant value.The friction surface morphology and volume wearing rate were used to characterize the wear behavior of fabric composites.With the increase of speed,PTFE film was gradually worn out and Kevlar fiber began to break out.The more serious the fabric structure damage,the larger the volume wearing rate was.With the increase of the load,the formation of PTFE film is more complete,the coating more Kevlar fiber,and the wear depth is also deeper,but the volume wearing rate decreases.It is concluded that the application range of composite material is 100-200 r/min,34.7-52 MPa.Moreover,by comparing the friction and wear behavior of PTFE/Kevlar fabric composites before and after modification,the influence of wettability on the friction and wear properties of PTFE/Kevlar fabric composites was studied.The friction coefficient of the samples with good wettability showed better tribological performance under the same conditions:the friction coefficient was as low as 0.15,the wear depth was shallow,and the volume wearing rate decreased to 1.80×10-5 m3N-1m-1.Therefore,the single-side modification of KrF excimer laser can not only improve the bonding property between fabric and matrix,but also improve the friction and wear properties of PTFE/Kevlar fabric composite. |
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