Experimental and analytical study of the effect of variable amplitude loadings in VHCF regime

摘要

Components and structures (e.g.helicopter rotors,wind turbine components or wheelset axels) arecommonly exposed a very high number of cycles with variable amplitudes.For the study of the influence ofvariable amplitude loadings in the very high cycle fatigue regime different load-time-histories up to 109cycles are used,which have different amounts of small amplitudes beneath the fatigue strength of theinvestigated material.The experiments are performed with an ultrasonic fatigue testing system withfrequencies up to 21 kHz.In order to avoid an excessive heat development of the specimen,pulsed loadingswith adequate pause lengths are applied.Therefore,only block loadings can be realized.The usedload-time-histories have been counted by the rainflow method and then divided into different number ofclasses providing that within every class a minimum number of cycles restricted by the experimentalperformance is given.The classes have been reconstructed to a load-time-history by varying the sequence ofthe classes.The influence of the different reconstructions as well as of the amount of the amplitudes beneaththe fatigue strength is quantified by the fatigue lifetime.These experimental data are used to proofconventional analytical approaches (Palmgren-Miner′s rule) of structural durability in the VHCF regime.