TWI Industrial Member Report Summary 293/1985
By T R Gurney
Fatigue tests have been carried out on specimens with non-load-carrying fillet welded attachments on the edges of the stressed plate using both very short loading blocks and Rayleigh and Laplace type spectra. The tests with short loading blocks on as-welded specimens showed that the 'design rule' derived in previous work was more satisfactory than Miner's rule for that situation. With stress-relieved specimens, however, neither rule was wholly satisfactory and it is clear that there is a need to allow for the non-damaging parts of the subsidiary load cycles. The results obtained with the Rayleigh and Laplace spectra showed a distinct tendency for sigma (n over N) to increase with block length and also with the peak stress in the spectrum. The alternative rule was safer at short and intermediate block lengths but showed a tendency to become unsafe at very long block lengths. There appears to be scope for using both rules for design purposes, depending upon the particular condition of peak stress and block length under consideration.