Required Fatigue Strength (RFS) for evaluating of spectrum loaded components by the example of cast-aluminium passenger car wheels

Abstract This paper displays, through the example of a cast aluminium wheel (G-AlSi7Mg0.3 T6, i. e. EN AC-42100 T6 or A 356 T6), the evaluation of critical areas through the method of Required Fatigue Strength (RFS). The RFS-values are derived from the local design spectra of the most critical areas of the component by searching the position of local particular Woehler-lines resulting in the prescribed allowable damage sum Dal within the cumulative damage calculation by the modified Palmgren-Miner hypothesis according to Haibach. The RFS-value is nothing more than the knee point of the calculated Woehler-line with defined slopes and cycle position of the knee point. As long as the production process delivers a material quality, i.e. a component related fatigue strength exceeding the calculated RFS-values, the required service durability is fulfilled. The paper demonstrates, through the example of a cast aluminium passenger car wheel, the evaluation of critical areas through RFS-values derived from the local design spectra of the most critical areas of the component and the experimental verification of the required service durability for 300,000 km and load occurrence probability of Po,Load ≤ 1%.