Study On The Mechanical Properties Of Circular Section Carbon Fiber Braided Composite Tubes

In the 2D braided composites,the fiber of the braided composites is entangled with each other,which shows a strong integrity,making the axial compression and impact resistance better than those of the traditional composite tubes.The excellent mechanical properties of the composites are closely related to the braiding process of the reinforcements and the properties of the resin.Firstly,in view of the phenomena that the carbon fiber breaks and damages easily due to brittleness of the yarns during 2D braiding,the process performance of carbon fiber filament yarn is analyzed by tensile test and homemade yarn porcelain eye corner wear test.The experimental results reveal that the breaking strength of the carbon fiber is much higher than that of other fibers,but it's extensibility is poor.Some precautions during winding yarn tube are discussed.Several 2D braided fabrics with different technological parameters are braided on a C24 ingot braiding machine.The effects of the braiding technology on the appearance and mechanical property of the 2D braided fabrics are studied.The factors that affect the wear degree of carbon fiber in the guide yarn eye successively are take-away force,guide yarn angle and braiding speed.Under the condition that the number of braided yarns is constant,the braiding pitch decreases,the square metre weight of the 2D braided fabrics increases,the pilling is serious,and the tensile fracture strength of the fabric decreases.Secondly,by optimizing the composite process of 2D braided composites tubes,the carbon fiber composite tubes containing higher carbon fiber content were made.The axial compression performance test of the tubes fittings were carried out,and the influence of braiding parameters on the volume content and axial compressive properties of the composite tubes fittings were analyzed and discussed.The results show that the optimized composite process can keep the fiber volume of the composite tubes between 20%-40%,while the inner diameter of the composite tubes is consistent.In the case of constant braiding speed,with the decrease of the braiding pitch,the braiding angle gradually increases and the fiber volume fraction increase too.When the braiding pitch reduces to a certain extent,fiber volume content increases slowly,while the compressive strength increases firstly and then decrease.When the braiding angle is 46 degrees,is the compressive strength reaches to the maximum.At the same time,the impact resistance test of composite tubes fittings were carried out by means of impact resistance equipment,andthe variation trend of force displacement during the key failure process were analyzed.Finally,the 3D geometric model of the 2D braided preform was established by using SolidWorks software,and the weaving direction and weaving condition of the braided yarn were simulated accurately.