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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]

Abstract: C/SiC composites with three preforms (carbon fiber needled bulk felt, Type A; stacking carbon fiber cloth followed by stitching, Type B; alternatively stacking carbon fiber cloth and unidirectional layer of carbon fiber tows followed by stitching, Type C) were prepared by precursor infiltration and pyrolysis (PIP) process, and then machined into M8 nuts and bolts. The influences of different preform, machining method and machining time, on the thread shape and properties of C/SiC nuts and bolts, were studied. The parameters to prepare C/SiC nuts are optimized as machining time at 9 PIP cycles and textile reinforcement structure of Type B preform. Compared with turning as bolt machining method, grinding method gives better thread shape. The average tensile strengths of C/SiC bolts (grinding machining) with three preforms are 95.9, 180.3, 243.2MPa, and shearing strengths are 59.5, 69.8, 106.3MPa, respectively. The tensile strength retention ratios of all the three bolts after oxidation in air for 20min are over 90% at 1000°C and about 80% at 1200°C. The bearing loads of the external thread teeth are 1895N, 4324N, and 3670N from Type A, B, C preforms, respectively. [Copyright &y& Elsevier]

A new tow-spreading technology was employed to spread T700SC 12 K fibers to a width of 12 mm, based on which plain weave carbon cloth with a low areal density of 100 g/m 2 and the thickness of 0.1 mm was obtained. 2D C/SiC composites reinforced by such T700 carbon cloth, together with T300 3 K plain weave carbon cloth (200 g/m 2 areal density) for comparison, were prepared by precursor infiltration and pyrolysis process. Chemical vapor deposition pyrocarbon (PyC) interphase was also used to modify the surface structures of both fiber reinforcements. The mechanical behaviors of the composites were predominantly affected by the in situ strength of carbon fibers as well as the relationship between the surface characteristics of carbon fibers and the material interface. T300 composites failed in a brittle mode, whereas T700 composites displayed a non-brittle fracture behavior. Mechanical properties of both composites were improved by PyC interphase. T700 composites with PyC interphase had a homogenous fiber-matrix structure and exhibited the optimum mechanical property, with the flexural strength, flexural modulus and shear strength of 425±23 MPa, 37±3 GPa and 24±2 MPa, respectively. [ABSTRACT FROM AUTHOR]