Tightening characteristic of C/SiC composite threaded fasteners at room temperature

The tightening characteristic of threaded fasteners made of C/SiC ceramic matrix composite at room temperature was investigated. Through experiment the relationship between torque and clamping force was measured during tightening and loosening process, meanwhile, the loss rate of clamping force in short or long time was recorded and the condition of wear on the thread surface was observed using microscope. In addition, the effect of material’s nonlinear tensile behavior on the tightening state was also analyzed. The results indicate that there is an approximately linear relationship between clamping force and tightening or loosening torque, and the average friction coefficients of thread and bearing surfaces are 0.52 and 0.46, respectively. As the tightening torque increasing, some wear abrasion occurs on the thread surfaces which, however, will weaken the effect of embedment process between engaged threads, and hence reduces the loss rate of clamping force and promotes its stability after assembly. After proper pre-tension treatment on the bolt in order to increase the elastic limit of the material, the anti-loosening capacity of the fastener can be improved.