Study On High-Low Cycle Fatigue Life Prediction Method For Hatch Corners Of Large Container Ship

Because the container ship has the characteristics of large opening in the cargo hold area and narrow side width,the stress concentration in the hatch corner is obvious,which is the prone and frequent part of fatigue failure.Generally speaking,the failure form of hull structure due to fatigue damage belongs to the fatigue problem of low stress level and high cycle period.However,when the ship encounters extreme sea conditions,due to the stress concentration at the corner,the stress may be close to or even exceed the material yield limit,which eventually leads to the low cycle fatigue failure of the structure under less extreme cyclic load.Therefore,the fatigue damage caused by complex load during the service of super large container ship which has experienced severe sea conditions for many times can be regarded as high-low cycle composite fatigue problem.Therefore,a high-low cycle composite fatigue calculation method based on spectral analysis method is proposed in this paper,which can consider the fatigue failure of alternating high cycle and low cycle loads.The main research contents of this paper are as follows:(1)This paper introduces the existing methods to evaluate the fatigue performance of hull structure,compares and analyzes the advantages and disadvantages of the existing fatigue calculation methods,and puts forward a high-low cycle composite fatigue model which can uniformly characterize the high cycle and low cycle performance.At the same time,uniaxial tensile test and low cycle fatigue test are carried out,the test pieces,working conditions and data measurement scheme are briefly introduced,the required parameters for establishing high and low cycle composite fatigue model are obtained and sorted out,and the accuracy of the model is verified by comparing the low cycle fatigue test value with the predicted value of the model.(2)Based on the high-low cycle composite fatigue prediction model established above,this paper takes a 4600 teu container ship as the research object,and adopts the code simplification algorithm,design wave method,spectral analysis method and composite fatigue method to obtain the fatigue life of hatch corners at different parts.By comparing and analyzing the differences between several methods,the influence of low cycle fatigue corner life caused by extreme sea conditions is discussed,and a new idea is provided for the fatigue performance evaluation method of hull structure.(3)In view of the conclusion that the prediction result of high-low cycle composite fatigue life is greater than that of ordinary fatigue life,the influencing factors of highlow cycle composite fatigue in hatch corner are discussed in this paper.For the external load factors,the effects of different wave dispersion diagrams,speed and wave direction on the diagonal fatigue life are discussed in this paper.For the influencing factors of hatch corner itself,the influence of corner size and type on stress concentration and fatigue life is analyzed by establishing a corner local refinement model.