The Stress-Strength Interference Method Applied to Fatigue Design: The Independence of the Random Variables

The use of the probabilistic analysis called Stress-Strength Interference Method (SSIM) applied to the endurance limit approach is being analyzed. Mean stress effect is often included to modify this fatigue limit. Plus, through the use of K factors, the fatigue limit is usually modified to account for the influence of loading mode, temperature, component size, corrosion, roughness... A necessary assumption of the SSIM is that stress and strength are independent. In this study, the independence of stress and strength is discussed. It appears that those variables may be in fact dependent. This error may lead to unconservative reliability predictions.