| With the development of science and technology,the application area of C/C composites is gradually expanded,but owing to the low bonding degree of the interfacial between carbon fiber and matrix,it is easy to produce fiber-matrix debonding,and the low intensity of matrix carbon,which is also easy to crack and then lead to material failure.Therefore,in order to improve the comprehensive properties of C/C composites,it is necessary and feasible to modify them.Previous studies have shown that nano carbon fiber is an ideal material for further improvement of C/C composites,but there is no in-depth research on the strengthening and toughening mechanism of nano fiber modified C/C composites(CNF-C/C).In this paper,numerical simulation method is adopted to analyze the enhance mechanism of CNF-C/C composite materials,the propagation of crack which is perpendicular to the interface can not be achieved by the basic function of ANSYS at this time,the extend finite element program be written to achieve this function.The effect of various factors on the material properties and the toughening mechanism of C/C composites and CNF-C/C composites were studied by using ANSYS combined with the extended finite element program,the main work is as follows:(1)Verify the feasibility of the extend finite element program firstly.The C/C composite model without pre-existing cracks was adopted to compare the results of extend finite element program and the results directly by ANSYS simulation.The simulation results is consistent with each other,which verifies the feasibility of this program.(2)According to the conceptual model of the C/C composite and CNF-C/C composite,and the theoretical formula,the effect of nano fiber modification on the toughness of C/C composites was proved,the reasons for the improvement of the mechanical properties of CNF composites were analyzed,and the influence of nano fiber content was estimated by this model;(3)The propagation of pre-existing crack in C/C composites and CNF-C/C composites,which perpendicular to the interface,comparative analysis with the result of calculation can be observed that the addition of nanofibers indeed enhance the performance of C/C composites,because of the addition of nano fibers increase the bonding strength between carbon fiber and matrix,which is same as researchers previous study;(4)The crack propagation in CNF-C/C composites with different fiber length of nano fiber were simulated,all other conditions are the same except for the length of the fiber.The result show that with the increase of nano fiber length,the degree of crack deflection decreases,which proved that the longer the length of the nanofibers,the stronger the degree of bonding between carbon fiber and matrix,and the better CNF toughening effect of C/C composites.(5)The crack propagation in CNF-C/C composites with different elastic modulus of the matrix were simulated.It can be seen that crack deflection degree gradually decreases with the increase of elastic modulus of matrix under the same load,which means that fiber is not easy to be pulled out,and CNF has better toughening effect on C/C composites.(6)The crack propagation in CNT-C/C composite materials with different content of nanofibers were simulated.According to the result,crack deflection degree decreases with the increase of the nanofibers content,namely with the increase of nanofibers content,the more difficult to debonding between carbon fiber and matrix,the better CNF toughening effect of C/C composites. |
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