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Fatigue damage model for welded joints of perpendicular plates

2015; Taylor & Francis; Volume: 29; Issue: 11 Linguagem: Inglês

10.1080/09507116.2014.937598

1754-2138

Janusz Kozak, Zbigniew Górski,

Fatigue and fracture mechanics

Fatigue cracks occurring in ship structures are formed in areas particularly susceptible to variable loads, i.e. areas of stress concentration, which include welded joints. In the case of fatigue cracking of complex welded structures, which include ship hulls, the cracking process can be divided into two stages: propagation of the crack in the direction of thickness and the development of the crack across its width. In addition, some of the fatigue cracks develop unseen and cannot be noticed by an observer (inspector), due to the conditions in which the inspection takes place (a ship standing in the dock, places prone to cracking are generally difficult to access, contaminated, located in closed and unlit spaces). In order to clarify the mechanism of formation and development of fatigue damage in complex welded structures, fatigue tests were carried out for a model of a welded joint of perpendicular plates within the model of a ship's structural node, determining the strength of the hull. The test model was a replica of the bilge node (area where the ship's side joins with the bottom) of a ship, created on a scale similar to real life and subjected to a sinusoidal oscillating alternating load, which corresponded to the load present in the actual structure, induced by inertial forces due to the acceleration of the structure subjected to lateral rolling of the vessel. Based on the results of the analysis, a two-stage model has been proposed for fatigue destruction of the vessel's bilge node, based on which an analytical method (utilizing the methodology of nominal stress and fracture mechanics) has been developed to determine the fatigue strength of complex nodes of ship structures.