Microstructure Modeling And Prediction Of Effective Properties Of 3D Needled C/C Composites

Carbon fiber reinforced Carbon composites(C/C)are widely used in aerospace engineering and automotive industry because of their low weight,high strength,high thermal conductivity,low expansion coefficient,excellent frictional performance and good thermal shock resistance.Unlike traditional C/C composites,3D Needled C/C Composites is fabricated by preforms which prepared by needle punching technology and matrix of Pyrolytic Carbon.Compared with the two-dimensional laminated C/C composites,3D Needled C/C Composites overcome the problem of weak strength between the laminate layers.Compared with the carbon felt C/C composites,mechanical properties and the ablation resistance of 3D Needled C/C Composites are improved significantly.The excellent mechanical performance and high engineering reliability make the 3D Needled C/C composites attractive in aeronautic and aerospace engineering.Therefore,it is of great value to investigate the microstructure modeling and prediction of effective properties of 3D Needled C/C Composites.Establish a reasonable microstructure model of 3D Needled C/C composites is the foundation of elastic properties prediction,damage analysis and optimal design of composites.The microstructure model has an important influence on the accuracy of predicted results.According to the microstructural observations of 3D Needled C/C composites,a two-step modeling technology is employed to generate the geometrical models of unidirectional fiber reinforced composites and randomly distributed short fiber reinforced composites.Then,the geometrical model of the overall 3D Needled C/C composites is created.The elastic properties of 3D Needled C/C composites are predicted based on the microstructure models of composites.The elastic properties of unidirectional fiber reinforced composites are predicted by using the Mori-Tanaka method and the strain energy-based finite element method.The elastic properties of randomly distributed short fiber reinforced composites are predicted by using Mori-Tanaka method.The elastic properties of the overall composites are predicted via the strain energy-based finite element method.The results of numerical calculation and experimental test are compared.The numerical prediction of elastic moduli of short-chopped fiber felts coincide well with the experimental result.It is shown that with the same fiber volume fraction,elastic moduli of short-chopped fiber felts decrease with the increase of pore volume fraction.In addition,numerical results of elastic moduli of the overall composites show a good agreement with the experimental results as well.Failure analysis of 3D Needled C/C Composites is investigated.The maximum stress criterion is used to analyze the progressive damage of 90° unidirectional fiber ply,needled fiber bundle and short-chopped fiber felt.The ACK model,exponential degradation model and the shear-lag model are used to analyze the progressive damage of 0° unidirectional fiber ply.A progressive failure analysis procedure is established and the failure behaviors of 3D Needled C/C composites are predicted.The needle density has a significant influence on the elastic modulus and failure behavior of 3D Needled C/C composites.The numerical results indicate that as the needle density increases,the tensile modulus Ex and shear modulus Gxy are both decreased,while the tensile modulus Ez and shear modulus Gyz are gradually increased.The numerical results also show that the increase of needle density exacerbates the failure of composites.The tensile strength of the composite is reduced with the increase of needle density.The mechanical properties of 3D Needled C/C composites are influenced by the microstructural parameters.Therefore,in this study the key parameters of microstructure model are designed to minimize the amount of failure and maximize the tensile strength of 3D Needled C/C composites.The results show that a reasonable designed needle density and fiber volume fraction can effectively reduce the amount of failure and significantly increase the tensile strength of the composites.