Research On Low Cycle Fatigue Of Ship Stiffened Plate Based On Fracture Mechanics

The fatigue strength of ship’s structure has very important significance on thesafety and survivability. At present all the research achievements and applications offatigue strength are basically for high-cycle fatigue of ship hull structures. Along withthe increasing in ship dimensions and more use of high-strength steel in recent years,the stress and deformation of ship structures are so high and large, which result invery prominent problem of low-cycle fatigue damage to large-scale ships. This hasbecome the key issues demanding prompt solution in the development of large-scaleships. In this paper the low-cycle fatigue crack initiation life of ship stiffened platebased on local stress-strain method has been studied; based on the crack propagationtheory of fracture mechanics, the paper has developed a method to determine thestress intensity factor of stiffened plates with cracks both in the stiffener and the plate.At the same time, the low-cycle fatigue crack propagation life and stress intensityfactor of ship stiffened plate are analyzed in the paper, hoping that the research workcan provide more reliable reference for the prediction of low-cycle fatigue of shiphull structures.The paper mainly includes the following aspects:(1)Systematically summarizing current study methods and progress on low-cyclefatigue of ship hull structures, briefly studying fatigue propagation life of ship hullstructures and its influenced factors on the basis of fracture mechanics, introducingthe fracture theory.(2)Using local stress-strain method and combining damage mechanics theory,the crack initiation life of ship stiffened plate is studied, the fatigue calculation andanalyses are achieved with MSC.Fatigue.(3)A procedure for evaluation of the stress intensity factor of stiffened plateunder uniaxial tensile load has been proposed, allowing for the existence of an edgecrack in stiffener web and a central through crack in plate. The Paris displacementformula、the variational principle are combined with the deformation compatibilityequation to define the stress intensity factor. (4)The stress intensity factor at the crack tip changing with stiffener’s spacingand stiffness of ship stiffened plates is studied in the paper. The crack preventioncharacteristics is also analyzed.(5)The low-cycle fatigue crack propagation life of initial crack ship stiffenedplate is carried out with virtual crack closure technique (VCCT) and Paris crackgrowth rate formula is also introduced to evaluate fatigue crack life. The low-cyclefatigue life of ship stiffened plate has carried on the preliminary forecast in order toprovide some ideas for further research.This paper expounds the effects of variable factors on low-cycle fatigue life ofship stiffened plate in different aspects, it is the development on the theory of fatiguestrength analysis and application. The research work has some referenced value forthe prediction of low-cycle fatigue of ship hull structures.