A B S T R A C T The paper deals with the fatigue and failure analysis of serial shot-peened leaf springs of heavy trucks emphasizing on the influence of thermal treatment and shot peening on fatigue life. Experimental stress-life curves are determined by investigating smooth specimens subjected to fully reversed rotating bending conditions. These test results are compared to corresponding ones determined from cyclic three-point bend tests on shotpeened serial leaf springs in order to reveal the influence of the applied thermal treatment and shot peening process on the fatigue life of the high-strength steel used for leaf spring manufacturing, dependent on the load level. Microstructure, macro-and micro-hardness analyses are performed to support the analyses and explain the effects resulting from the certain shot peening process on the surface properties of the high-strength spring steel under investigation. The assessment of the fatigue results reveals nearly no life improvement due to the manufacturing, emphasizing the necessity for mutual adjustment of shot peening and thermal treatment parameters to take account for life improvement. D = diameter E = Young's modulus f 1 , f 2 = fatigue endurance strength correction factors K = slope of the stress-life curve HB = Brinell hardness M σ = mean stress sensitivity factor N f = number of cycles till specimen rupture R = stress ratio R = radius R m = ultimate tensile strength R z = mean roughness depth σ a = stress amplitude σ E,a = endurance stress amplitude σ m = mean stress I N T R O D U C T I O NHigh-strength steels are used in various technological fields, particularly in the industry of spring manufacturing. Especially in the automotive industry, leaf springs constitute the most effective suspension way of commerCorrespondence: G. Savaidis.

The prediction of the crack initiation lifetime in consideration of the statistical and technological size effects will be introduced in course of an analytical model. To verify this method results from fatigue tests at constant and variable amplitude loads for unnotched and notched specimens of the aluminum alloy AA6009 will be considered.

In order to estimate the crack initiation lifetime of the aluminium alloy AA6009 an analytical model, based on local stress strain approaches will be presented. To calculate fatigue lifetimes of engineering components statistical and technological size effects have been taken into consideration. In addition, fatigue tests have been undertaken with load spectra, which are representative of stresses and strains actually experienced by the component during service.