Issue 33

V. Anes et alii, Frattura ed Integrità Strutturale, 33 (2015) 309-318; DOI: 10.3221/IGF-ESIS.33.35 317 Figure 11: Block extraction methodology for random loadings. During the block extraction, it can be established the inherent unitary damage of each block as follows in Eq. (8): _ ,max,ssf,block 1 unitary block f block D N vcc  (8) Eq. (8) shows the methodology to estimate the unitary damage within a loading block. On the left, in numerator the number 1 is related to the number of loaded blocks, which in this context is 1. In the denominator, it is represented the material fatigue strength when subject to a loading block, where ,max,ssf,block f N is the fatigue life estimate based in the maximum value of the SSF equivalent stress within a loading block, and block vcc is the virtual cycle counting regarding each extracted block. In order to estimate the instantaneous accumulated damage, the Palmgren-Miner rule concept can be used as follows in Eq. (9). . 1 ,max,ssf,block 1 i SSF random f block i D N vcc         (9) Eq. (9) represents the instantaneous accumulated damage value, which is updated block by block until . SSF random D reaches the value 1, which is the reference condition, considered here to estimate a high fatigue failure probability. F INAL REMARKS n this paper was discussed and analysed several aspects related to random multiaxial fatigue. First, it was discussed the importance of having multiaxial fatigue packages in which is contained multiaxial fatigue models synergistically linked, in order to deal with all fatigue phenomena in multiaxial random fatigue. Second, it was presented the SSF equivalent shear stress damage parameter where it was focused the SSF physical foundations. Third, it was presented the virtual cycle counting method to evaluate a block damage and finally it was presented how the SSF equivalent stress in synergy with the virtual cycle counting method can be used to estimate random accumulated damage under multiaxial loading conditions. A CKNOWLEDGEMENTS he authors gratefully acknowledge financial support from FCT – Fundação para a Ciência e Tecnologia (Portuguese Foundation for Science and Technology), through the project PTDC/EME-PME/104404/2008 and through IDMEC, under LAETA, project UID/EMS/50022/2013. I T