Preparation And Properties Of C / C Composites With Wrap Strap

Needle punching process is a technology for producing carbon fiber preforms, which has advantages of low cost, simple processing, short fabricating times, high automation and easily preparing complicated and thin-walled preforms. These exceptional properties made the process as a very important method to produce the preforms used as the nozzle of rocket motor. In this work, four typed preforms of cylindrical shape were designed and produced by means of combining the the axial, circumferential and angled plies of continuous carbon fibers with wrapping tapes. In these preforms, the preform 1# was prepared by alternate lamination of circumferential tape and continuous fiber layer with a step-wise needle punching. The preform 2# was made of circumferential tape,circumferential long fiber layer, and axial long fiber layer. The preform 3# was fabricated from circumferential tape, circumferential long fiber layer, axial long fiber layer and angled laminated long fiber layer. The inner-layered structure of preform 4# was similar to the preform 1#, and its outer layer was made of axial long fiber layer, circumferential long fiber layer and angled laminated long fiber layer. The thickness of 1#~3# preforms were20 mm, while the inner and outer layers of preform 4# were 10 mm.These tape-wrapping needle-punched preforms were densified by chemical vapor deposition to produce carbon/carbon(C/C) composites of density of 1.55~1.60g/cm3. The influences of the preform structures on the mechanical and thermal-physical properties of the composites were investigated. The relations between the structures and the properties of the composites were also discussed, which was important for the applications of the tape-wrapping needle-punched C/C composites in the nozzle. The main conclusions are following:The structure of these preforms was studied by scanning electron microscope. The results show that the laminated plane is constituted of discrete short fiber felt and continuous long fibers. The needle-punched fiber bundles are found in the radial direction,which is formed from the discrete short fibers by needle-punching. The needle-punched fiber bundles traverse the tape layers, continuous fiber layers, and the fiber felts to form a2.5-dimensional structure.The matrix microstructure of the composites was studied by polarized light microscope. The results show that the matrix of the composites produced from preform1#~3# is dominated by smooth laminar(SL) pyrocarbon(PyC). For the composites obtained from preform 4#, a thin layer of rough laminar(RL) PyC is formed on the surface of the SL layer. The composite 2# has a higher axial tensile strength of 33.54 MPa. The reason is attributed to the higher axial fiber volume fraction about 8.6% caused by the laminated non-woven fibers. Meanwhile, the composite 2# has higher compression strength in the axial and radial directions which reach 110.0MPa and 130.8MPa,respectively. The composite 1# with wrapped tape and continuous long fibers has higher tensile strength of 88.9MPa in this direction due to the higher fiber volume fraction(15.3%). The composites of higher flexural and shear strength can be produced from preform 4# because the long fibers are laminated in the axial, circumferential and angled directions. The flexural strength, axial and circumferential shear strength of the composites are 94.9MPa, 9.7MPa and 10.6MPa, respectively. The four typed composites’ axial and circumferential tensile strength increase with the higher fiber volume fraction.The axial and radial specific heat capacity(Cp) of these four typed composites increase with an increasing testing temperature from 25℃ to 1000℃, while they show a similar Cp under a same testing temperature. The thermal conductivity(λ) increases as the testing temperature rises from 25℃ to 400℃. After 400℃, the axial λ exhibits a slight decline, whereas the radial λ tends to increasing slowly. The composites 2# and 4# have lower thermal expansion coefficient(α) due to the long fibers introduced into their axialand angled directions.From above, the mechanical and thermal-physical properties of the composite 2# is relatively outstanding of the four typed composites. The target properties of the composites can be reached by tailoring the preform structure. The optimized experiments confirm that the tape-wrapping needle-punching technology possess excellent designability in the processing and properties, which is a potential technology for fabricating the preforms of revolution objects.