Research On Designing And Processing Of Composite Bolt Fastener

With the development of the preparation technology and the reducing of the cost, carbon fiber has been used in many industries more and more widely, especially in aerospace industry, where there is an overpowering need for high-duty composite bolt fastener. With light weight, high strength, high corrosion resistance and high fatigue resistance, composite bolt fastener has a good application prospect, in this case, it is necessary to study the molding technology of carbon fiber reinforced polymer. By using molding tecnology, we could inerease the intensity of composite bolts, improve the surface quality and the size accuracy of the thread, so that it more widely applied to areas of structural connection.To determine the material system of molding compound, three resin systems, including TDE85 epoxy resin, SE300 CE and WIN1126 polyurethane resin, were characterized by a series of tests. The results of dynamic contact angle tests indicated that these three kinds of resin systems could infiltrate T700, T800 and T1000 carbon fiber well. Results of viscosity test showed that when the temperature was 100℃, SE300 CE got the lowest viscosity, 5 m Pa·s, which meant that fluidity and mould-filling ability of SE300 in molding could be better than the other two. TG-DTA results showed the highest Tg with 296℃ and Td with 326℃ belonged to SE300 CE, based on this SE300 CE could be supposed to have best thermal endurance property. The mechanical property of the resins is determined and the results showed that SE300 CE system has the highest tensile modulus, witn TDE85 EP system having the highest bending modulus. To comprehensively consider infiltration capabilities, thermal endurance properties, mechanical properties and manufacturabilities of three resin systems, SE300 CE was selected to be the matrix of CFRP moulding compound.By using ANSYS software, reasonable finite element models of composite material thread fasteners were established and simulation analyses in tensile, shear and torsion cases was conducted, through which the distribution regularity of stress, strain and displacement was founded. All the simulation results met the design requirements.A CFRP bolt compression mold with one vertical and one horizontal parting surface, by which fiber in bolts could be homogenized, was designed by AutoCAD platform. With winding pattern calculated, adopt the method of spiral winding and manufactured CF/CE moulding compound by a 45° winding angle. Then manufactured CFRP bolts by compression molding, with molding temperature 220℃ and molding pressure 200 MPa. Fiber content measuring showed bolts’ rod and screw tooth got the fiber weight content of 55%, 35% respectively. Mechanical tests showed that tensile strength of bolts was 330.55 MPa and shear strength of bolts was 704.56 MPa, which meant this CFRP bolt had excellent mechanical properties. In addition, pulled-off thread in tensile tests illustrated many studies were needed to further improve the screw strength of CFRP bolts.