Numéro : 2723 - Year : 2017
About crack propagation in design
Michel HUTHER, ITG, Consultant (Paris - France)
Since many years the Miner sum is, although often criticized, the basic method for the fatigue verification of the marine structures. The critics concern the physical validity due to its linear evolution versus time and the unknown state of the structure corresponding to the failure criteria. However the return experience shows a good correlation with the in-service reality. In front of this approach the crack propagation provides a non linear growth versus time in conformity with measurements on samples and with in-service crack observations and clearly defines the type of failure corresponding to the failure criteria. As this approach is more realistic, it appears possible to replace the Miner sum by this approach. However it must be recognized that this replacement does not always correspond to the capacity of the design offices for the fatigue verification calculations in design. The aim of this paper is to analyse the reasons of this state of fact, knowledge and difficulties, and to propose a solution coherent with the Miner sum approach which allows the crack propagation method application by design offices for the fatigue verification in design.