• Fatigue assessment of current FKM guideline is too conservative for nonproportional loading. • New normal stress-based approach significantly improves accuracy. • Proposals are validated using an extensive database with fatigue test results. The guideline “Analytical Strength Assessment” is a stress-based framework for evaluating the fatigue strength of safety-relevant components. However, it possesses significant weaknesses when dealing with multiaxial nonproportional stresses, often leading to results that are unnecessarily conservative and which waste valuable component potential. This study addresses these shortcomings by proposing two new calculation procedures designed to be compatible with the existing framework of the guideline: a normal stress-based approach using modified scaled normal stresses and a shear stress-based approach inspired by the Findley parameter. Both methods utilize a critical plane approach in combination with a nonproportionality measure and a multiaxiality grade to adjust the S-N curves and mean stress correction. The accuracy of these proposals is validated using a comprehensive database containing fatigue lives for various materials, including steel, cast iron, and aluminium, under both proportional and nonproportional multiaxial loading. The evaluation confirms that the current guideline is highly conservative for nonproportional loading and shows that changes to the algorithm of the guideline can increase accuracy for both nonproportional and proportional stresses, thereby making significantly higher fatigue performance accessible
Wächter et al. (Fri,) studied this question.
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