Multiaxial Fatigue Simulation Of Tubular Joints On Marine Structures

Most marine structures are welded by steel pipes.Because tubular joints arelinked by weld,under the effect of the structure of those tubular joints and welds onthem, stress concentrations will be easily found near the intersecting line.Because thesafety of tubular joints will affect the safety of ocean structures directly,so tubularjoints is the critical and dangerous parts of marine structures,and the the fatigue ofthem will cause the failure of ocean structures. Above all, it is of important to studythe multiaxial fatigue damage of ocean structures combined with their workenvironment.Normally, the working condition of marine structures is very poor，and most ofthose conditions contain wind waves and ocean current.In the long-term effects ofthese loads, fatigue damage will occur in those marine structures,and failure willhappen with the cumulative of fatigue damages.The failure of those structures cancause security and economic losses. Therefore,it is meaningful to study multiaxialfatigue of the ocean structures.The force with the composite of wind, waves, currents,marine structures showing a multiaxial property, correspondingly the fatigue of oceanstructure presents a multiaxial property too.Compared with the previous study onuniaxial fatigue, multiaxial fatigue can reflect the actual situation of marine structuresmore property, it can also explain the fatigue failure mechanism more property too.As the working environment of the marine structures becomes deeper,and theocean conditions becomes more dangerous,it is very important to find a multiaxialfatigue model to study the phenomena and predict the life of multiaxial fatigue.Thereare a lot of problems are not solved about the evolutionary mechanisms of multiaxialfatigue,and there is no theoretical system is approved in the academic field yet.This paper mainly discusses the mathematical model of ocean currents and waveloads,find the simplified form of these loads to simulation ocean structures by the useof finite element software. Since most of the management nodes work below the surface of the water,So built the offshore platform model and analysis the dynamicand static performance under ocean loads by Ansys software,then extract a specialK-joint to analysis its multiaxial stress and fatigue feature.Preliminary discussions thedistribution of stress and fatigue life of the pipe node under multiaxial loading indifferent forms.The analysis mainly focuses on the stress and fatigue lifecharacteristics appropriate to the actual situation of multiaxial loading case of theK-joint weld location.Finally, calculate the initial crack presence of the stress intensityfactor of the material,and those findings can provided preliminary groundwork for themultiaxial fatigue study of complex structures.