The influence of piston shape on air‐spring fatigue life

Abstract

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.

Rubber–fibre composite modelling and its influence on fatigue damage assessment

“…The results of the FE analyses (FEAs), which show equivalent von Mises stresses are shown in Figures 11 and 12. Previous measurements and research [5][6][7] on the used rubber-fibre composite have shown that damage normally occurs in the middle rubber layer. Therefore, only stresses in the rubber are given.…”

“…In the past, many papers have been published describing different methods for evaluating long-fibre rubber composites with respect to fatigue life. In particular, the research focuses on individual products such as tyres, [1][2][3][4] air springs [5][6][7][8][9] or hydraulic hoses, 10 but none of them really focuses on the finite element (FE) modelling technique applied to the product concerned. The research focusing on the influence of FEM model complexity on the results of the analysis 11 shows that model complexity has a great influence on fatigue life prediction, but it does not go as far as to address micro modelling and the influence of different modelling techniques on fatigue life prediction.…”

Determining influential factors for an air spring fatigue life

“…For L 27 (3 13 ) array, several standard linear graphs are available, but only the one presented in Figure 3 Researchers have shown that the critical plane approach gives good predictions of the rubber components fatigue life. 5,6,10,[21][22][23] These investigations of natural rubber's fatigue life have shown that crystallization of natural rubber has a significant impact on its fatigue life. [24][25][26][27][28][29][30] Reinforcement by rubber crystallization occurs, when stress ratio R > 0.…”

“…With increasing and decreasing piston diameter, the air spring's effective diameter D eff is increased or decreased. Stresses can be determined using finite element analysis [5][6][7][8][9][10] hence, the design and operating conditions of an air spring can be changed using simulations to determine changes in the maximum , lever eccentricity; e p , eccentricity; h, height; h d , design height; IT, number of interactions; l, lever length; LV, number of levels; n, number of experiments; p, air pressure; R, stress ratio; T, quality characteristic average; y i , quality characteristic; α, inclination; ϑ, temperature; ϑ 0 , absolute zero temperature; b μ, prediction average; σ acp , stress amplitude calculated with critical plane approach; σ x , stress in the x direction; σ y , stress in the y direction; τ xy , shear stress; ϕ, cord angle stress. This progressive spring stiffness characteristic allows a similar amount of comfort whether the vehicle is fully loaded or empty.…”

“…[2][3][4] If a prediction of fatigue life is required, stresses on the air spring flex member must first be determined so that S-N curves can be calculated. Stresses can be determined using finite element analysis [5][6][7][8][9][10] hence, the design and operating conditions of an air spring can be changed using simulations to determine changes in the maximum Nomenclature: a, Shomate equation gas constant; b, Shomate equation gas constant; c, Shomate equation gas constant; c p , heat capacity at constant pressure; d, Shomate equation gas constant; d i , flex member inner diameter; D o , flex member outer diameter; DF, degrees of freedom; e, Shomate equation gas constant; e l , lever eccentricity; e p , eccentricity; h, height; h d , design height; IT, number of interactions; l, lever length; LV, number of levels; n, number of experiments; p, air pressure; R, stress ratio; T, quality characteristic average; y i , quality characteristic; α, inclination; ϑ, temperature; ϑ 0 , absolute zero temperature; b μ, prediction average; σ acp , stress amplitude calculated with critical plane approach; σ x , stress in the x direction; σ y , stress in the y direction; τ xy , shear stress; ϕ, cord angle stress. Such changes in maximum stress ultimately influence the fatigue life of an air spring.…”