| In recent years,the natural gas market in China has developed rapidly,as a result,the numbers of gas storages and high-pressure natural gas wells have been increasing gradually,therefore,the market demand for gas-tightness detection instrument is also increasing.The rubber is the core component of the instrument to provide an enclosed detection space,of which the material properties and size parameters are related to the sealing capability.This article uses ABAQUS to establish the first compression and the second compression finite element model of the rubber,and,with the use of reasonable simulation methods,the optimized rubber material and size parameters are obtained through simulation analysis,and the prototype production of the sample is completed,and the full-scale experimental table is built.Through experiments,the scientificity of the established model and the simulation method are verified,which provide basis for the design and optimization of the rubber of the gas-tightness detection instrument..The main research contents and results are as follows:(1)For the three kinds of hydrogenated nitrile rubber material commonly used in gas-tightness detection instrument,the specimens are made with reference to the relevant national standards.Then uniaxial compression and uniaxial tension tests are performed to obtain stress-strain curves.The existing hyperelastic constitutive model is used to fit the curves.By comparing the degree of fitting,the most suitable constitutive models are selected respectively for each rubber material,which provide an accurate description of mechanical behavior for rubber during the modeling process.(2)Combining the three selected constitutive models of rubber material,the finite element model of rubber of the 31/2" instrument under first compression is established on ABAQUS.In order to solve the problem of the large deformation,three simulation methods,mesh to mesh mapping,automatic stabilization and quasi-static analysis are used.The results show that under the same conditions,QMF-2 has a better sealing capability among three rubber materials,so it is used as the rubber material of gas-tightness detection instrument.(3)According to relevant literature,in the process of the first compression,the maximum value of the contact stress of rubber in its’ outer surface is used as the evaluation standard of the sealing capacity.Orthogonal test with three factors and four levels is designed,and then the simulation analysis of rubber of the 31/2" gas-tightness detection instrument under different size parameters is completed.The range analysis of the simulation results show that the external diameter among each size parameters has the greatest influence on the sealing capability of the rubber after first compression,followed by the internal diameter and the height,hence,the largest external diameter should be taken into consideration in the scope of engineering permission.The optimal size paremeters of the rubber of the 31/2" instrument are 72mm in external diameter,36mm in internal diameter,120mm in height.(4)In order to solve the problem that the maximum contact stress of the rubber with optimal size in the result of the simulation analysis of the first compression is still smaller than the annular pressure,which cannot give the answer whether the designed rubber meets the requirements of the actual detection operation,the finite element model of rubber of the 31/2" instrument under second compression is established on ABAQUS.In the process of the second compression,the ultimate annular pressure that can be withstood by the rubber under certain axial pressure is used as the evaluation standard of the sealing capacity.Orthogonal test with three factors and four levels is designed and then the simulation analysis is completed.The range analysis of the simulation results show that the rules obtained by the second compression are basically the same as that obtained by the first compression with mesh to mesh mapping method in all pressure levels and automatic stabilization method in the range of 30MPa.Based on this,the simulation of the second compression of the rubber under the actual loading sequence of the instrument is preformed,through which the four groups of rubber selected in the orthogonal test are re-optimezed,and the result shows that the optimal size parameters of the rubber are still 72mm in external diameter,36mm in internal diameter,120mm in height,therefore these sizes are used as the actual sizes of the rubber.Simulation studies have shown that this particular rubber is conservatively estimated to meet the requirements of the actual detection operation within the range 30 MPa.(5)Based on the optimal rubber material and size parameters obtained from the simulation analysis and optimization design,the development of the 31/2" instrument is completed,and a full-scale experimental bench simulating the on-site working conditions is established,then experimental study on the sealing capability of the rubber is carried out.The experimental results verify the accuracy of the second compression simulation analysis,and prove that the use of two simulation methods,mesh to mesh mapping and automatic stabilization,and the use of the evaluation method for sealing capability of the rubber under first compression are basically reasonable.In addition,the experimental results prove that the designed rubber can meet the requirements of the actual detection operation within the range of 50MPa.Through the research in this paper,a set of experimentally verified finite element simulation models and analysis methods for the first and second compression are established for the study of the rubber of the gas-tightness detection instrument,which provides the basis for the design and optimization of the rubber of the instrument.In this paper,through the comparison of the simulation results of two stages and the experimental data,the application scope and accuracy of the three simulation methods,mesh to mesh mapping,automatic stabilization,and quasi-static analysis,are determined in solving the problem of large deformation of rubber.The results have important guiding significance for the finite element simulation analysis of rubber. |
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