Study On Influence Of Weaving Angle On Mechanical Properties Of Double Carbon Fiber Composite Pipes

The three-dimensional braided composite material is a textile structural material which is woven into a three-dimensional monolithic fabric by a weaving technique and then composited with a matrix(resin,metal,etc.).Compared with laminated composite materials,it overcomes the shortcomings of low interlayer strength and easy delamination after being stressed.Because of its high specific strength and excellent mechanical properties,it is widely used in aviation,aerospace,military and civil fields.However,due to the complex structure of composite fiber bundles,this paper aims to study the axial compression of three-dimensional braided composite pipe and the mechanical properties of three-point bending,and to explore the effect of different combinations of double-layer braiding angle on the mechanical properties of composites.Through the full-scale macrostructure model finite element analysis method,the axial compression and three-point bending mechanical properties,failure process,stress distribution and propagation were pre-tested,and the failure mechanism was studied.The main content of this paper:(1)Simulation part.The three-dimensional modeling of the woven fiber is carried out according to the spiral trajectory of the fiber braid and the fiber cross section obtained by CT scanning.The selected fiber is an orthotropic material,the resin matrix is an isotropic material,and the direction is performed on the woven fiber.Define the local coordinates in the fiber direction and fiber radial direction,predict the basic mechanical parameters of the composite by the unit cell model,apply it to the macroscopic structural model,analyze and analyze the deformation process and stress of different composite double-layer braided composites.distributed.(2)Experimental part.First,input different extraction speeds on the display screen of the ring knitting machine to obtain the corresponding angle of the woven fibers.When the two layers of fiber weave angles are different,the weaving will produce a transition,resulting in inconsistent knitting angles of the same layer,so at the end of the mandrel.Plus a transitional mandrel.Then,the woven fiber and the resin matrix were cured by VARTM molding process.After the pipe was formed,the pipe fittings were cut using the standard recommended by American ASTM.Finally,the pipe fittings were quasi-static axial crushing and three-point bending experiments.Record the mechanical process of the pipe.(3)Contrasting and analyzing the finite element simulation results and experimental results,including comparing the load-displacement curves and failure processes and morphologies of the two,thus verifying the validity of the finite element analysis of macrostructures.The main conclusions of this paper:(1)Axial crushing.The load-displacement curves of several braided angle composite pipe fittings are relatively close,and they all rise linearly approximal.When the material begins to fail,it drops sharply.When the material is completely destroyed,the curve tends to be gentle.During the crushing process,stress concentration occurs at the end of the material,the material is partially damaged,the fiber is stressed more than the resin,and the fiber is subjected to the main load.The resin acts to bond the fiber into a whole,protect the fiber,and transmit stress.The maximum stress of the outer layer fiber is greater than the maximum stress of the inner layer fiber,and the outer layer fiber is subjected to the main load.Different weaving angles,the material’s compressive performance is different.The rule is that the smaller weaving angle can withstand large loads,but the material failure process is relatively rapid,the load decreases greatly,and the load is less in the later stage.(2)Three-point bending.The load-displacement curves of several braided angle composite pipe fittings are linearly increasing upwards first.When the material begins to fail,the load decreases slowly.At the later stage of failure,the load tends to be gentle or decreasing.Similarly,during the bending process,stress concentration occurs in the portion where the sample contacts the indenter,and the outer layer fibers are subjected to the main load.The bending strength and flexural modulus of the smaller knitting angle are relatively large,and the bending resistance is better.(3)The results of finite element analysis are in good agreement with the experimental results,indicating that it is more economical and effective to predict the influence of braiding angle on the mechanical properties of composites by finite element analysis.