Study On Mechanical Properties Of Carbon/carbon Composite Structure Based On Needled Technology

Carbon/carbon(C/C)composites have the advantages of low density,good thermal conductivity,low friction resistance and thermal expansion coefficient.Its applications in aerospace and automotive industries are quite commons.The preform structure is an important factor in determining the performance of the C/C composite.The needle-punched preform transfers the fibers in the XY plane to the Z-direction through a needling process to form a unique three-dimensional structure.The needled punched C/C composite overcomes the shortcomings of easy delamination of two-dimensional laminated C/C composites and makes up for the complicated process and ineffective densification of three-dimensional braided C/C composites.More and more applications and attention have been paid to it.The tensile,compressive and bending properties of the needle-punched C/C composite are tested.the stress-strain curves and strength are obtained.Considering the meso-structure of needle-punched C/C composites,the representative volume element models with random and uniform distribution of needle-punched positions are established respectively.The effective elastic properties of the two models are calculated by finite element method and compared with the experimental values.The longitudinal tensile strength of needle-punched C/C composites is mainly determined by the longitudinal fiber content.Therefore,as long as the longitudinal fiber content is known,the tensile strength can be estimated by using the uniaxial composite tensile strength calculation model.Considering the randomness of the tensile strength of fibers and the interfacial shear strength between fibers and matrix,a model for calculating the longitudinal tensile strength of unidirectional composites is established.An example shows that the method presented in this paper is effective.The needling process will cause damage to the fiber.Therefore,it is necessary to determine the longitudinal effective fiber content.A resin-based composite reinforced by needle-punched preform is prepared.the longitudinal effective fiber content is about 7.3% using the tensile strength test value to deduct.The tensile strength of the needled punched C/C composites is estimated by using the calculated effective fiber content.and compares with the longitudinal tensile strength test values of C/C composite reinforced by the same needle-punched preform with an error of 4.68%.The bending properties of needle-punched C/C composites were studied by experimental tensile and compressive stress-strain curves.Firstly,a three-point bending model was established in the Abaqus finite element software.The load-displacement curve was obtained.Next,the statistical strength theory is introduced.It is assumed that the strength of needle-punched C/C composites obeys the Weibull distribution.The relationship between flexural strength and tensile strength is studied.The proportional coefficient between bending strength and tensile strength was derived.Finally,the finite element model of rocket engine nozzle is established.Taking needle punched C/C composite material as an example,the thermo-mechanical coupling analysis of rocket nozzle is carried out,and the temperature field and stress field distribution are obtained.The structural strength under heating condition was checked.