| For non main load-bearing structural components,if the yield stress exceeds the local structure,the elastic design criterion should not be used to evaluate the integrity and safety of the structure,because it will seriously limit the design space of the structure.For this kind of problem,the elastic-plastic design criterion can be used to evaluate the safety of the structure under the premise of plastic deformation's existence.Shakedown criterion is a widely used elastic-plastic design criterion for structures subjected to alternating loads,because it can give full play to the plastic bearing potential of materials,so that the structure can obtain more design space.After years of development,three kinds of numerical analysis methods have been formed for shakedown analysis,including successive cycle,theoretical calculation,standard formula calculation,etc.However,the successful cases of applying shakedown criteria to engineering in China are still limited,because the existing shakedown analysis process is not simple enough or lack of auxiliary program tools.Therefore,this paper focuses on the applicability improvement and auxiliary analysis tool development around the typical shakedown analysis method,and carries out the research work related to the validation of effectiveness.The main research contents are as follows:Firstly,the applicability of the successive cycle method and a theoretical analysis method(stress compensation method)are improved and the auxiliary program tool is developed.The related research contents of successive cycle method are as follows: 1)The elastic-perfectly plastic model is replaced by Chaboche model,which has stronger ability to simulate ratcheting;2)The program tool of chaboche model parameter fitting is compiled.The related research of stress compensation method is as follows: 1)The calculation formula of residual stress in the stress compensation method is simplified to realize the unification of the calculation formula of residual stress under mechanical load and thermal load;2)The influence of temperature on material parameters is introduced,so that the influence of temperature difference on shakedown analysis can be considered more accurately;3)An auxiliary program tool for shakedown analysis of stress compensation method is developed.Secondly,based on numerical examples of different load types,the applicability and accuracy of different shakedown analysis methods are compared.In addition to the two improved methods,a classical code calculation method(stress classification method)is also considered.The numerical results show that the improved method has good accuracy,and the program tool also has good applicability.Among the three methods,the results of the successive cycle method and the theoretical analysis method have little difference,while the results of stress classification method are sometimes quite different.The results based on Chaboche material model are lower than that of the elastic-perfectly plastic model,which indicates that the elastic-perfectly plastic model is not necessarily conservative.Because the improved stress compensation method only needs to perform linear elastic analysis,it is more efficient than the successive cycle method in determining the shakedown boundary.Finally,a test system for structural shakedown under alternating thermal load is introduced.The system can indirectly judge whether the structure is shakedown or not through the residual deformation history of the structure.Compared with the traditional high temperature stability test method,it has significant economic advantages.Based on the temperature difference load model,3D printing was used to complete the processing of the test piece and the shakedown test was carried out.The numerical results show that the shakedown limit of the external alternating ambient temperature peak is higher than 600?.In the experiment,three conditions of 100?,300? and 500? were considered,and the test results all showed that the structure was shakedown,which was consistent with the numerical results.The results show that the test system is feasible in shakedown test. |
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