Complexity of Determining the Fatigue Strength of Real Structures Under Random Vibration Conditions—Two Case Studies

Fatigue failure remains a major concern in the design and performance evaluation of machine components and structures as it accounts for a significant proportion of mechanical failures. This article presents a fatigue evaluation methodology based on SN (stress-cycles to failure) curves to understand and predict the fatigue behaviour of complex components under various loading conditions with widely varying device geometry and dynamics. In order to accurately interpret and utilize the SN curves, the paper outlines key factors influencing material fatigue, including stress amplitude, mean stress, stress concentration, environmental effects, and surface finish. The integration of these factors into the SN curve-based assessment is discussed to tailor fatigue evaluations to specific machine components and structures. To demonstrate the practical application of SN curves in fatigue assessment, two case studies of machine components and structures are presented. The paper ends with a summary and conclusions, the most important of which is that the greatest impact on design fatigue life consists of accurately estimated stresses resulting from the load conditions and the dynamics of the structure.