| River-Sea-Going ship(RSGS)plays an important role in Yangtze River shipping by its unique advantages.At present,the government has also issued relevant policies to promote the development of RSGS.Although there are good opportunities for the RSGS,there is no reference regulation for their fatigue strength assessment.If referencing GUIDELINES FOR FATIGUE STRENGTH OF SHIP STRUCTURE and defaulting the whole life in the sea,then the structure weight of RSGS will increase and lead to the gross dead weight tonnage decrease,rising costs.Moreover,this method directly ignores the effect of load interaction between river and sea on fatigue strength.Therefore,it is necessary to carry out basic research on fatigue assessment of RSGS.From this,according to the route characteristics of RSGS,this paper simplifies the river and sea wave load into small-large two-step alternating load and one type is selected for fatigue test,which is the intersection between longitudinal and transverse bulkhead.The crack propagation process is studied by combining fatigue tests with numerical analysis,in order to provide a scientific basis for the establishment of fatigue strength assessment of RSGS.The main research contents and conclusions are as follows:(1)The fatigue test was carried out by means of comparative tests,two model under constant and three under two-step alternating load,aiming at the effect of different load history on crack propagation life.The results show that the higher load is the main force driving crack propagation.Conservative results will be obtained if only the effect of higher load on damage is considered.Under this test condition,participation of lower load reduces crack growth rate under higher load cycle and increases crack propagation life.Different load history has different effects on crack propagation life.When the ratio of lower load to higher load is 3:1,the life improves obviously.(2)Based on fracture mechanics,the simulation method of crack propagation under constant amplitude load is studied.The effects of initial defects and residual stresses on crack propagation life are considered by using the software FRANC3 D and ABAQUS.Finally,this method is used to simulate the crack propagation process,and the variation regularity of stress intensity factor is given.The crack propagation life and crack propagation path are compared to verify the reliability of the simulation method.(3)The influence of different load history on the range of effective stress intensity factor is discussed.The correction factor of effective stress intensity factor considering the effect of small load is put forward under the specific load-history ratio and load-amplitude ratio.The results show that when the crack length is in the half width of weld toe,the lower load has a significant effect on the crack propagation life under higher load cycle.When the crack length extends to about 14 mm,the effect is the greatest.When the crack length exceeds half width of weld toe,the effect decreases gradually,but it is still advantageous to improve the crack propagation life. |
PDF Full Text Request