抄録
Setting treatment is ordinarily given to helical springs in order to improve the fatigue strength and to suppress the fatigue deformation. The effectiveness of setting treatment on helical springs has been proved by several experiments, and recently the authors examined this effect on curved leaf springs, which verified the same availability. The beneficial effect of setting seems to arise primarily from two factors, favorable residual stress and work hardening.
As to the measurement of residual stress in helical springs, no calculation formula according to the dissecting method is found as yet due to the complexity of their shape. In practice, the helical springs shaped by the coiling machine are likely to have triaxial residual stresses as well as torsional one, being in an extremely complicated state.
In this study, as a first step, the problem was limited to measure only the torsional residual stress introduced by setting, and along this line a new calculation formula was derived. Helical springs of the material SUP 2 were heat treated in two ways, that is, tempered at the temperature of 450°and 500°C separately, and then subjected to setting treatment. Fatigue tests were made in partly pulsating compression with both springs, which showed an effectiveness of setting distinctly. Residual stress measurements were carried ont using a new formula, at the stress levels above and below the fatigue limits, and the changes in residual stresses were examined. The results were in quite good agreement with those obtained previously.
