Study On Properties Of Multi-axial Warp-knitted Carbon Fiber Reinforced Composites

With the rapid development of modern industry,it is urgent to develop functional materials with not only lightweight and corrosion resistance,but also high strength,abrasion resistance and strong designability.Traditional fiber-reinforced composites are difficult to meet the harsh working conditions due to the insufficient strength,stability and wear resistance,such as impact,extrusion,drawing,vibration,friction,etc.These disadvantages seriously restrict their development.In this paper,multi-axial warp-knitted carbon fibers(MWKCF)with good stability,orientation and designability,excellent resin infiltration and conductivity were used to prepare composites.The preparation technology,mechanical properties and friction properties of multi-axial warp-knitted carbon fiber reinforced composites(MWKCFC)were studied.On the one hand,these studies aim to develop of composites with high strength,wear resistance and high reliability.On the other hand,these studies aim to improve the service life of composites under harsh working conditions and provided theoretical basis and guidance for the engineering application of MWKCFC.The main contents of this paper are as follows:(1)In order to solve the performance defects in the preparation process of MWKCFC,the preparation methods of composites were optimized,including surface pretreatment methods of carbon fibers,resin curing process,vacuum process and surface quality of composites.Fiber surface pretreatment included four kinds of MWKCF fibers,followed by biaxial(±45°),biaxial(0°/90°),triaxial(±45°/90°)and quadriaxial(?45°/0°/?45°/90°).The research showed fiber pretreatment can significantly improved the properties of the interface between fibers and resins.Vacuum process could significantly improve the internal defects of MWKCFC.After vacuum treatment,the impact strength of the biaxial(±45°)composite could reach 50KJ/m~2 and the compressive strength was 308.6MPa,which the increase was more than 40%.The surface quality of MWKCFC could be effectively improved by using resin release agent.(2)The impact and compressive properties of four kinds of composites were tested by the cantilever beam impact tester and the universal tester.The damage and failure mechanism of composites were revealed.The impact properties of four kinds of composites were analyzed.It was found that the impact properties of four kinds of MWKCFC were very good,the impact strength of triaxial(±45°/90°)composites was the most outstanding.Test under 11J impact energy,the impact strength of triaxial(±45°/90°)composites could reach109.38KJ/m~2,which was 2.18 times of the impact strength of the biaxial(±45°),1.5 times that of the biaxial(0°/90°),and 1.7 times that of the quadriaxial(-45°/0°/+45°/90°).The damage modes and damage mechanisms of composites with different reinforced structures were found to be different.The effect of laminated fibers on impact properties was different,of which 90°laminated fibers had the largest contribution to the impact performance,followed by±45°,0°laminated fibers were the worst.The compressive properties of MWKCFC were tested.It was found that the compressive strength of MWKCFC increased with the increase of fabric knitting angles.The compressive strengths of biaxial(±45°),biaxial(±45°/90°)and triaxial(±45°/90°)were 308.6MPa,457.7MPa and 516.6MPa.The compressive strength of four-axis(?45°/0°/?45°/90°)composites was the highest,reaching 696.8 MPa.It could be seen that the compressive performance of MWKCFC could be significantly improved by increasing the angles of fabric laying.By studying the compression failure modes of composites with different reinforced structures,it was found that with the increase of fabric laying angles,the failure of composites became difficult,the resistance to crack propagation increased and the bearing capacity of composites increased.(3)Friction and wear properties of MWKCFC were studied by means of the spherical disc friction,the scanning electron microscopy(SEM)and the laser confocal microscopy(LCM).The effects of rotational speed,load and temperature on the friction performance of MWKCFC were tested.It was found that the friction coefficient and wear rate decrease with the increase of load and speed.When the speed was 800r/min and the load is 20N,the minimum friction coefficient was about 0.108.Compared with rotating speed and load,temperature had a greater influence on the friction performance of composites.With the increase of temperature,the friction coefficient and wear rate of MWKCFC increased quickly,which indicates that MWKCFC were suitable for use in low temperature environment,and high temperature could accelerate the damage of composite surface.By further comparing the friction and wear properties of traditional plain carbon fiber reinforced composites and MWKCFC,it was found that MWKCFC had obvious advantages in friction performance.Under the same working conditions,the friction coefficient of MWKCFC was35%lower than that of plain weave,and the friction stability was higher.These fully showed that MWKCFC could not only obtain excellent mechanical properties,but also obtained good friction properties.