Effects of material and geometric parameters on the room-temperature compressive behavior of ceramic matrix composite helical springs

Ceramic matrix composites (CMC) possess low density, excellent high-temperature resistance, and good damage tolerance, making them attractive for elastic components operating in extreme environments. In this study, a series of C/SiC and SiC/SiC cylindrical helical compression springs were fabricated via chemical vapor infiltration (CVI), and the effects of densification degree, preform architecture, fiber type, tow size, and geometric parameters on room-temperature compression behavior and cyclic response were systematically investigated. The results show that the CMC helical springs exhibit pronounced hysteresis during room-temperature compression, and the damage evolution is dominated by matrix microcracking, interfacial debonding, and frictional sliding. For the C/SiC springs, the spring rate shows a strong linear positive correlation with material density, increasing from 0.54 to 5.09 N/mm as the density rises from 1.48 to 2.01 g/cm³, an increase of approximately 8.4 times. Compared with the two-dimensional circumferential braided structure, the three-dimensional four-directional braided structure increases the spring rate by 38.5%. Increasing the tow size from 1 k to 6 k raises the spring rate from 3.69 to 4.52 N/mm. The SiC/SiC springs exhibit higher spring rate than the C/SiC springs. In addition, the spring rate decreases with increasing pitch and increases with wire diameter. After 1000 room-temperature compression cycles, the spring rate retention ratios of the C/SiC and SiC/SiC springs remain 97.9% and 96.0%, respectively, indicating good cyclic stability.