Effects of fiber preform structures on the mechanical properties of C/SiC nuts and bolts

Carbon fiber-reinforced silicon carbide (C/SiC) nuts and bolts (M8) with different fiber preform structures were prepared by precursor infiltration and pyrolysis. The influences of fiber preform structures on the mechanical properties of C/SiC nuts and bolts, as well as the failure behaviors of threaded joints were studied. A C/SiC nut, which was fabricated by using the preform prepared by stacking 3K carbon fiber cloth followed by stitching, had the highest shearing strength (64.5 MPa). The bolt with the preform prepared by alternatively stacking 3 K carbon fiber cloth and unidirectional layer of carbon fiber tows followed by stitching had the highest extreme tensile strength (243.2 MPa) and shearing strength (106.3 MPa), but low thread tooth bearing ability (3.5 kN) and critical thread engagement length (9 mm). It is suitable for applications emphasizing the extreme tensile or shearing strengths of threaded joints or possessing enough thread engagement length to ensure bolt rupture as the failure mode. The bolt with the perform prepared by stacking 1K carbon fiber cloth followed by stitching had the highest thread tooth bearing ability (5.0 kN) and the lowest critical thread engagement length (6 mm), as well as moderate extreme tensile strength (163.0 MPa) and shearing strength (82.1 MPa). It works effectively for applications concerning thread tooth strength or possessing limited thread engagement length. Therefore, the preform for preparing a C/SiC bolt should be selected according to its application requirements.