Theory And Experiment Technique Research On Integrity Of Structure Welded In-plane

With the improvement of the level of welding technology.“welded connection in-plane”block assembly technology has been applied to civil ship construction of domestic largeshipping enterprises. The use of “welded connection in-plane” assembly technology providesfavorable conditions for segment no allowance assembly, reduces the workload of two hullsassembling on the shipway greatly and shortens the product development time and productioncycle effectively. However, after adopting new technologies, whether the strength of the hull,stiffness, residual stress and welding deformation, fatigue life and so on will have greaterimpact later and how is the influence degree and so on have not been researched anddiscussed in depth.In this paper, on the basis of theoretical research and experimental comparison,numerical prediction method of residual stress of typical welded joint was established anddistribution rule and its impact on the ultimate strength of structure was also analyzed. Basedon the multi-scale theory, the formula of ultimate strength of typical welded joint with crackwas obtained through a large number of calculations. Failure evaluation on typical weldedjoint was carried out through introducing new R6failure judgment figure and the criticalcrack length was calculated. Fatigue life prediction under different initial crack lengths andthe ultimate and fatigue strength experimental research of typical welded joint were carriedout. Through the systematic study of the paper, the main research results are as follows:1) Through the comparison between numerical simualtion and experimental value ofplate butt welding, the finite element numerical simualtion method of the welding process oftypical welded joint was established. The numerical simualtion research on weldingtemperature field, stress field of typical welded joint under different docking technologies wascarried out and the distribution and characteristics of welding temperature field, stress field oftypical welded joint was obtained.2) The influence of different matches of boundary fixed way and welding materialstrength on residual stress and displacement fields was researched. Results show that residualstress and displacement fields of typical welded joint under different docking technologiesand boundary fixed ways will redistribute, but the maximum value of residual stress anddisplacement are not influenced. Different welding material strength matches has a certaininfluence on residual stress, between which the maximum difference value is80MPa. 3) The method of combining multi-scale theory with finite element technology wasapplied to ultimate bearing capacity of defect structure with micro crack. Process of thisresearch was divided into two parts using constitutive approximation method, namelymesoscopic and macro size model. Using constitutive approximation method, mesoscopic sizemodel of plate with micro crack was as the part different from conventional material propertyin the macro structure of typical welded joint. Basic orthogonal table calculation scheme wasestablished and then ultimate strength of the overall structure was calculated.4) Formula of ultimate strength of typical welded joint under different docking formsincluding three variables of relative crack length(RCL), crack distribution depth(CD) andproportion(CRD)was obtained through a large number of calculations. Based on formula ofultimate strength, influence of relative crack length(RCL), crack distribution depth(CD) andproportion(CRD) on ultimate bearing capacity of typical welded joint were carriedrespectively. And the influence of welding residual stress on ultimate strength of structure wasresearched.5) Based on the failure evaluation results of new R6failure judgment figure, failureevaluation on typical welded joint was carried on. The failure path curve was obtained byfailure evaluation. According to the ailure path curve, the critical initial crack length of typicalwelded joint was obtained. The research on minimum crack length which proposed at chapterthree was carried on. The results of the study provides a powerful reference for structureintegrity assessment.6) Failure evaluation on typical welded joint under four stress levels of167MPa,220MPa,335MPa and418MPa was carried on based on new R6failure judgment method.Critical crack sizes of different working conditions were obtained by failure evaluation. Crackcritical size of evaluation point obtained from new R6failure judgment figure was comparedwith test result. It also coincides well with experimental result.7) According to the micro crack size adopted above, fatigue life prediction on typicalwelded joint with initial crack was carried out. Through the prediction, relation curve betweeninitial crack length and fatigue life was obtained. Initial crack length of the actual structurewas also obtained through the comparison between fatigue test result and fatigue lifeprediction value of typical welded joint.