Abstract
The large pitch angle of a coil spring required by higher design stress generates multi axial stress condition. As a result, the correctness of Wahl's stress equation in large pitch angle coil springs seems to be questionable to conduct a fatigue life assessment. It seems urgent to establish the characteristic stress suitable for fatigue life assessment as well as to study the effect of residual stress and surface roughness. The research committee conducted a variety of fatigue tests and stress evaluation using finite element analysis in order to investigate followings.
1) Which stress, such as maximum principal stress, maximum shear stress or Misses stress, is most suitable for estimating fatigue life?
2) How can we evaluate the effect of residual stress?
The test results come to the conclusion that the correlation of fatigue life and maximum principal stress is higher than the other stress condition.
