A series of comparisons between some of the most common procedures for fatigue measurement of welded structural components are carried out. The load cycles are of a stochastic nature, typical of those associated with naval structures during their lifetime. The superstructure of a tanker ship is subjected to non-simultaneous stochastic loads due to wave motion and to those of calm water. The maximum value of the stresses in both load histories is assumed to equal to 80 N/mm2 whilst the mean periods are 10 seconds and 7 days, respectively. The cumulative damage produced is estimated using a dual parameter counting method (rainflow method) and a single parameter counting method (range-pair counting method). Both approaches have been finalised to the evaluation of the lifespan according to the procedures envisaged in the British Standard (BS) and Germanischer Lloyd (GL) regulations which, currently, appear to be the most accredited in the field of fatigue measurement in naval structures. From the results, the following considerations can be drawn: The damage calculated by the single parameter method is equal to approximately 70 % of that calculated by the rainflow method for load histories with a high number of cycles whilst, in the case of load histories with a low number of cycles, it even appears negligible (9 %) with respect to those calculated by the dual parameter method. The calm water load, although inducing stresses of the same amplitude as these produced by wave motion, produces a cumulative damage completely negligible with respect to that attributable to the action of waves. Whichever counting procedure adopted, the total damage calculated by the GL procedure is underestimated with respect to the BS; meaning consequently the lifespan calculated by the GL overestimated with respect to that calculated by the BS.
Evaluation of the fatigue resistance of welded structures for naval use
Welding International ; 17 , 6 ; 451-465
2003
15 Seiten, 26 Bilder, 10 Tabellen, 24 Quellen
Aufsatz (Zeitschrift)
Englisch
Algorithmus , Auswertemethode , BS-Norm , Ermüdung bei hohen Lastspielzahlen , Ermüdung bei niedrigen Lastspielzahlen , Ermüdungswiderstand , Haltbarkeit , Lastwechsel (Lastspiel) , Markov-Prozess , Matrix (Zahlenschema) , Norm , Parameterschätzung , Schadensakkumulation , Schiffsaufbau , Schweißkonstruktion , Schwingungsermüdung , Spannungswelle , stochastisches Verfahren , Tankschiff , Wasser , Zählverfahren , Zugbeanspruchung
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