TWI Industrial Member Report Summary 365/1988
By T R Gurney
The primary objective of this work was to determine the extent to which the fatigue life of specimens subjected to loading spectra, in which the mean stress of the individual cycles varied, differed from that for specimens subjected to the same spectra with either the mean stress or the minimum stress held constant. The spectra were so arranged that their rainflow counts were identical in spite of the changes in mean stress.
Since the work was exploratory in nature it was necessary to restrict the range of parameters which were studied. Thus, tests were only camed out on one type of specimen (a plate with longitudinal non-load-carrying fillet welded edge attachments) using two basic spectra, both with the same block length (128 cycles), at two stress levels (maximum ranges of 275 and 175 N/mm2). The results have been assessed in terms both of Miner's rule and the 'area' rule proposed by the author.