Influence Analysis Of Welding Residual Stress On Fatigue Strength Of Ship Structure

Ship is a class of large and complex welded structure. It is subjected to dynamical loadsinduced by wave, cargo and ballast water pressure. Under the effect of these dynamical loads, thehull structure is prone to fatigue failure phenomenon. In recent years, with the widely use ofhigh-strength steel in ship and ocean engineering structures, the problem of fatigue damage ofthe hull structure became prominent. In most cases, welded areas of the hull-structure are thevulnerable parts of the whole structure. The welding residual stress directly affects the fatiguestrength of the hull structure. So it is significant to analyze the influence of welding residualstress on fatigue strength of ship structure.A bulk carrier is taken as an example. This issue establishes three cabin structure model of abulk carrier by direct numerical calculation using the finite element method according toCommon Structural Rules for Bulk Carriers. After boundary conditions determined and meshed,finite element analysis model of three cabins is established. At the same time, considered theuniform loading, loaded compartment, normal ballast and heavy ballast loading conditions, aswell as each of the four loading conditions, the loads of ship structure fatigue are calculated.Then, fatigue hotspots are selected and the meshes near to hotspots are refined. Spot stresses ofselected hotspots are achieved by automatic analysis through compiled program of ANSYSAPDL. Further, the equivalent notch stresses of hotspots are obtained. Ultimately the cumulativefatigue damages of different spots are obtained. On this basis, four levels of welding residualstress on those same hotspots are considered. Compared and analyzed the results of the weldingresidual stress on the cumulative fatigue damage degree of each hotspot, it shows that thewelding residual stresses have a greater impact on the bulk carrier structural fatigue strength. Theresults have reference meaning to the relaxation method of welding residual stress and thefatigue strength of bulk carriers.