Preparation And Properties Of Carbon Fiber Composite Coil Springs

Helical spring has been widely used in various industries,and has received a lot of attention and research.Compared with metal materials,composite materials have broad application prospects in the field of spring due to their outstanding comprehensive properties.But their forming and processing are difficult,which hinders the research and development of spring.At first,in this paper,a new manufacturing process of composite helical spring based on Vacuum Assisted Resin Influsion(VARI)is developed,and the twistless parallel composite springs with different fiber content,twisted multistrand composite springs with different reinforcement twist and braided composite springs(single and double layer)with different braiding angles are prepared by using this technology.The torsion,compression and resilience of the composite spring are tested.And the influence of the parameters of the reinforcement structure on the mechanical properties of the springs was analyzed preliminarily.Then,a 3D geometric model is established to adapt to the characteristics of the internal reinforcement structure of each spring,and the mechanical properties of the spring under the axial compression load are simulated by numerical method,and the stress distribution law of different structural springs is revealed.Finally,the numerical analysis method is used to predict the change rule of spring constant of each spring under different influence factors.The results show that the new preparation process of the composite helical spring has high reliability,the actual fiber content of the spring is only 2.84% different from the theoretical value,and the spring has a smooth surface and low porosity.The compressive properties of composite helical spring are consistent with the torsional properties of composite rods.The compression properties of the composite helical spring with parallel twistless,twisted multistrand and braiding structure are increased successively.Compared with the parallel twistless spring,the spring constant of the twisted multistrand spring increased up to 62.83% at most,and compared with the twisted multistrand composite spring the spring constant of the braided spring increased up to 129.08% at most.With the increase of the fiber content of the parallel twistless spring and the twist of the twisted multistrand spring,the spring constant increases gradually,while the spring constant decreases with the increase of the braiding angle in the braided spring.In addition,the resilience of the composite spring is closely related to the spring constant.With the decrease of the spring constant of the composite helical spring,the resilience performance increases gradually,and the maximum resilience rate can reach 94.74%.In the numerical analysis,the stress values of parallel twistless,twisted multistrand and braided springs increase successively,and the maximum stresses are90 MPa,350 MPa and 830 MPa respectively.The angle-stress curves of the three kinds of springs in the initial coordinates of 0°?360° all show a sinusoidal trend.In the process of compression,there is a serious stress concentration phenomenon in parallel twistless spring,and the dangerous section is located in the inner diameter direction of the spring and the stress value is the largest when the initial coordinate is 180 °.In the twisted multistrand spring,the stress between the fibers in the structure is uniform.In the braided spring,the stress of the corresponding part of the braided structure changes little from the initial coordinate 0 ° to 360 °,and there are the small difference between the maximum and minimum value of the angle-stress curve in the initial coordinate0 ° ?360 °,which illustrate the structure is stressed uniformly.In the prediction of spring constant change rule,the spring constant increases rapidly with the increase of twist at first and then increases slowly with the increase of twist at three different fiber contents: 45%,50% and 55%.The relation formula between spring twist and spring constant is fitted as quintic polynomial.Besides,The spring constant of braided spring increases with the increase of braiding angle from 20 ° to 45 ° and then decreases with the increase of braiding angle.The relation between braiding angle and spring constant of braided spring is quadratic polynomial.