| There are many wooden fishing boats in China's coastal areas,which existed many issues such as long vessel age,old hull,easy to corrosion and so on.The upgrading of old fishing boats has been an urgent problem to be solved in the development of fishery in China.High density polyethylene(HDPE)fishing boats were taken as the research object in this paper based on the fishing boat replacement update development idea of "substituting plastics for steel and substituting plastics for wood ".Meanwhile,the direction of the fatigue life was chosen as the research content in order to let people have a better understanding of this type of ship,accelerate the upgrading of China's coastal old fishing boats,as well as enhance the fishery modernization process of our country.At present,the major fatigue assessment method of ship structure is the S-N curve method based on the assumption that the material has no defects.Because of the existence of crack defects and the lack of the S-N curve of HDPE material,the fatigue crack propagation theory and the structural finite element method was used to analyze and predict the fatigue life of the joints between the ship's stern bulkhead and the rear clapboard.The main research work of this paper included four aspects as follows.Firstly,the mechanical properties of HDPE marine plate were tested.These data were used to input the material properties and approximately simulate the material's curve for the subsequent finite element static analysis and the fatigue crack growth life analysis.Secondly,the construction process of the HDPE ships was summarized through investigation and research.Through the field investigation of the shipyard,the paper summarized the construction process of the HDPE boats and provided certain reference for the future construction of the ship.Next,the structural finite element analysis model of the HDPE ship was established and the static analysis was carried out to provide data for fatigue life prediction and evaluation.At last,the connection between the stern bulkhead and the rear clapboard was considered as the fatigue hotspot in the subsequent fatigue life study based on the linear constrained analysis results.And the mesh of the hotspot area was refined to provide a more accurate equivalent stress value for the further fatigue life evaluation.Finally,fatigue crack propagation life analysis was carried out for the hotspot.Based on the fatigue crack propagation theory,the fatigue crack growth life analysis of the hotspot was da/ dN-?Kcarried out by means of MSC.FATIGUE software and Paris law.The effects of different crack shape ratios and initial crack sizes on fatigue life were discussed,also the strength of the whole ship structure under the fault of the stern bulkhead was analyzed.Following conclusions were obtained in this paper:Firstly,stress and displacement distribution of the entire boat were obtained through the static analysis of the finite element structure.The numerical simulation results showed that the overall strength of the boat satisfied the requirements.Secondly,the connection between the stern bulkhead and the rear clapboard was considered as the fatigue hotspot in the subsequent fatigue life study.By analyzing the fatigue life of the fatigue hotspots,we could draw the conclusions that crack growth rate was accelerated with the growth of load cycles,and it was lower in the early stage of crack propagation.Propagation life occupied the most part of entire life.Next,the different crack shape ratio and the different initial crack size had a great influence on the fatigue life of the crack,but the life values were in the same order of magnitude.In the case of a0 and ?? unchanged,the N was increasing with the increase of the a/c.In the case of a/c and ?? unchanged,the N was increasing with the increase of the a0.Finally,when the stern bulkhead was broken over the deck,the strength of the boat was still satisfactory,but the hull stiffness at the side connected to the stern bulkhead was insufficient. |
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