Stress Cycle Counting Method and Predicted Life

Abstract

The predicted life of a rolling stock truck frame under service load history is greatly influenced by the cycle counting method selected and the S-N curve used. However, little words have been done to evaluate and select the most suitable counting method and S-N curve for the prediction.
In this paper, six kinds of cycle counting methods and three kinds of S-N curves were investigated by using the measured service stress data, and the predicted lives (a modified Goodman's method for evaluation of mean stress effect and a modified Miner's rule for fatigue damage calculation were applied) were compared to the service life.
The following results were obtained;
(1) Two cycle counting methods (the zero cross range pair and the zero cross range pair mean methods) showed the lives close to the service life, and the S-N curve B (which was used for the fatigue life prediction of fillet welded joint of truck frame by S. Tanaka) was good for the life prediction of the truck frame.
(2) When the effect of mean stress was taken into account, the lives under full load and vacant load conditions became a half of those without considering the effect.
(3) By using the zero cross range pair and the zero cross range pair mean methods for cycle counting and the S-N diagram B, the life under the full load condition was about 15% less than that of the vacant load condition.