Finite Life Fatigue

Constant amplitude loading with stress levels above the endurance limit cause material damage, crack initiation and after a limited number of loading cycles failure will occur. In case of measured loading histories or results from multibody simulations the resulting stresses can show strong fluctuations or even random behavior. In order to determine stress ranges and cycle numbers from random input counting procedures are used. For this purpose LIMIT offers a standard rain flow algorithm which determines stress ranges at different levels and the corresponding load cycle numbers. The stress ranges are ordered by magnitude and can be used to calculate the amount of damage, using the simple Miner damage accumulation rule. If stress levels above the endurance limit occur and cause damage, then the S-N curve usually changes its shape and all stress ranges above the cutoff level have to be taken into account as well. Stress ranges below cutoff do not contribute to damaging the material. This procedure is available within EC3, FKM and other codes.