1997 年 1997 巻 42 号 p. 55-60
Coil springs made of silicon nitride (Si3N4), which has higher strength and heat resistance than other ceramics, have recently developed. By examining the range of strengths and the heat resistance of the coil springs, it is shown that the coil springs can be used at temperatures up to 1000°C. Using Weibull failure theory, we derive an equation to calculate effective volumes of coil springs and examine the influence of effective volume on the strength of coil springs. The results show that the mean strength of coil springs decreases with increasing effective volume. Therefore the strength of coil springs can be estimated from an equation of the effective volume, and this equation can be used in design of coil springs. Furthermore, by conducting proof tests, coil springs that have relatively large defects can be eliminated and so only highly reliable coil springs can be placed in service.