Preparation and mechanical properties of C/SiC nuts and bolts

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, 243.2 MPa, and shearing strengths are 59.5, 69.8, 106.3 MPa, respectively. The tensile strength retention ratios of all the three bolts after oxidation in air for 20 min are over 90% at 1000 °C and about 80% at 1200 °C. The bearing loads of the external thread teeth are 1895 N, 4324 N, and 3670 N from Type A, B, C preforms, respectively.