The Influence of piston shape on air-spring fatigue life

This paper presents how the piston shape of an air-spring can influence both its load-deflection characteristic and the fatigue life. Two piston shapes are considered in this study for which load-deflection characteristics and fatigue lives are compared. A method for the estimation of air-spring fatigue life is upgraded by adding the influence of the mean stress level and afterwards used together with finite element analysis to predict the fatigue life and, ultimately, the timing and global location of failure within the air-spring. These predictions are then compared with measured results and show good agreement thus proving the validity of the method used here for calculating fatigue life. Both experimental and predicted results show that the highest fatigue life can be expected if a noncylindrical, back tapered piston is used. This is only the case if the air-spring is mounted at its optimal design height as the study also shows that moving away from optimal design height does have a detrimental effect on the fatigue life of back tapered air-springs. This is due to the appearance of higher stress amplitudes in the flex member during operation. Such stress amplitudes and consequently fatigue damage can be reduced by avoiding sharp transitions in the piston design that cause additional bending of the flex member in a direction opposite to the deflection in the flex member fold