1996 年 1996 巻 41 号 p. 7-11
By using new technique which enables us to measure the depth of initial fatigue cracks in springs, the mechanism of fatigue on engine valve springs was made clear:
(1) The initial cracks on non-electropolished springs start from the surface of wire. By contraries, on electropolished springs, they start from inside of wire.
(2) On non-electropolished spring, the depth of initial cracks has certain critical values, which probably depend on applied stress.
(3) When the initial crack on non-electropolished springs reaches the critical depth, failure occurs suddenly. On the other hands, when the initial crack on electropolished springs comes to surface, sudden failure takes place.