Preparation And Mechanical Properties For C/SiC Composites And Components

The reentry of space shuttle is characterized by very high heat loads, so thermal protection systems(TPS) is required to have high strength under thermal and mechanical loads. C/SiC composites as new thermostructure materials can comply with the requirements of TPS during the re-entry of spacecrafts.The structure and mechanical properties of TPS materials are analyzed in thisthesis. In addition, the two different connection method--threaded connection andrivet connection are also discussed. The main results of investigations are as follows,(1) 2D C/SiC materials are fabricated by RMI process. The extraordinary merit of this process is cost effective. The results show that the composites is extraordinarily dense, with density 2.31g/cm3, open porosity 1.39 % . The compression strength vertical and parallel to layer are almost the same, and the values are 418MPa and 409MPa respectively. The damage and failure behaviors are mainly determined by the failure modes of matrix, and the materials undergo brittle failure. Comparing the interlaminar shear strength of materials fabricated by RMI and CVI process, the former (43MPa) is higher than the latter (29MPa).(2) The needle-punched 3D C/SiC materials fabricated by CVI process is quite loose, with density 1.90g/cm3? open porosity 16.09%. The bending strength vertical to layers is less than the strength parallel to layers, and the values are 206MPa and 287MPa respectively. The compression strength vertical and parallel to layers are almost the same, and the values are 147MPa and 154MPa respectively, which are affected by the interface between non-woven cloth and short-cut fiber web. The interlaminar shear strength of materials is 27MPa, which is enhanced by the fibers vertical to layers.(3) The low cost manufacture method of C/SiC bolt and nut by CVI process are brought forward. The bolt and nut with specification M8 are manufactured with good integrality through this method, which is applying for a patent (already accepted). The fracture surface near the connection area between the screw and the bolt shank is desired with tensile strength 108MPa. The nuts withstand tensile loads withoutdamage.(4) The tensile strength of the plate with hole and plate filled with pin (with same outline dimension and different hole diameter) is tested. It is discovered that the tensile strength of plate with hole is decreased obviously from 173MPa to 119MPa with the increasing of hole diameter from Φ2.5mm to 06mm. The tensile strength of plate filled with pin is higher than that of the plate with hole, and reach maximum value 176MPa with pin diameter 04.5mm. The pin weakens the stress integration around the hole in a certain extent and reinforces the plate.(5) The tensile strength of riveted plate with pin diameter Φ3.4mm is tested. The result shows that controling the match clearance between the plates can ensure the filling of SiC matrix efficiently, which improve the integration strength between plates, and finally the ability to resist tensile failure increases.