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The influences of fiber preform structure and thread engagement length on the mechanical properties of Carbon fiber reinforced silicon carbide matrix ( C/SiC) threaded joints were studied. The results show that stacking 3K carbon fiber cloth followed by stitching is a good preform for preparing a C/SiC nut because of its high bearing ability. Stacking 1K carbon fiber cloth followed by stitching is a preferred preform to prepare a C/SiC bolt, and its minimum thread engagement length resulting in bolt rupture instead of thread spalling failure is 4 mm, which is obviously smaller than those of other bolts. [ABSTRACT FROM AUTHOR]

A new method to form helical C/ Si C spring is proposed. Using paraffin mold as a sacrificial core, unidirectional carbon fiber bundles (infiltrated with resin) are wrapped around the mold to form helical spring, and after resin curing, the mold is removed, leaving a preform of C/ Si C spring. Following densification is finished with precursor infiltration and pyrolysis ( PIP) process. The spring constant of C/ Si C spring reaches 7.88 N/mm and could be regulated by varying composite density and carbon fiber content. The spring properties could be improved by twisting the carbon fibers at 35-50 twist/m. The restoration ratio reaches 100%, but energy dissipation happens during unloading process. After oxidation in air at 1200°C for 10 min, the spring has an 82.4% spring constant remaining ratio. [ABSTRACT FROM AUTHOR]