engleski

Fatigue Strength Assessment of Ship Structures

Fatigue is responsible for a large proportion of failures occurring in welded ship structural details. The cracks occurred mostly on the side longitudinals at the connections to transverse bulkheads and transverse webs on all types of vessels. The loads responsible for fatigue are generally not large enough to cause material yielding. Instead, failure occurs after a certain number of load or stress fluctuations. For the purpose of developing the required unified procedure, many topics concerning the fatigue strength of hull structures (primarily tankers) have been reviewed and discussed in this paper. Required informations for evaluation of fatigue strength are: the material characteristics (cast in the form of S - N curves), long-term stress distribution (or stress histogram) of the structure, factors influencing fatigues strength (mean stresses, residual stresses, corrosion). Depending on how the long-term stress distribution is determined, the analysis procedure for fatigue assessment of hull structures can be defined as the so-called “spectral fatigue analysis” or as the so-called “simplified fatigue analysis”. This method is briefly presented here, as well as its crucial details such as: stresses to be used (nominal, hot-spot or notch stresses), S - N curves, Weibull shape parameter, total number of life-time cycles, fatigue design loads and other influencing factors.

Fatigue strength; ship structures; S-N curves; hot-spot stresses.

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