A STUDY ON STRENGTH CHARACTERISTICS OF SI3N4 COIL SPRINGS

Coil springs made of silicon nitride (Si3N4), which has higher strengt h and heat resistance than other ceramics, have recently been develope d. 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 tempera tures up to 1000 degrees C. We derive an equation to calculate the eff ective volumes of coil spring and examine the influence of size on the strength of coil springs. In addition, using a process zone size fail ure criterion, proof tests were conducted and analysed. The results sh ow that the mean strength of coil springs decreases with increasing ef fective volume. Therefore the strength of coil springs can be estimate d from the value of the effective volume, and this relationship can be applied in design calculations. Furthermore, by conducting proof test s, coil springs that have relatively large defects can be eliminated a nd so only highly reliable coil springs can be placed in service.