Finite Element Analysis Of Solid Expandable Tubular Forming Based On Twin-Shear Stress Yield Theory

With the increasing demand of oil and gas resources,there is a huge gap between domestic oil and gas supply,and it is increasingly urgent to develop oil and gas resources.Petroleum exploration and development have moved towards deep reservoir and ultra-deep reservoir,which makes oil exploration and drilling more difficult.The mono-diameter expandable tubular technology can avoid diameter loss of the oil wells during the wells drilling,which is the technical guarantee to achieve deep and ultra-deep wells.The theory of material constitutive is the theoretical basis for the development of expandable tubular technology.In this paper,the twin-shear stress yield theory is applied,and the combined method of theoretical deduction,numerical analysis and experimental verification is used to research the expansion force,residual stress and deformation in the forming process,which can provide a reference for material selection and structural design of the mono-diameter expandable tubular technology.The main work and conclusions of the thesis are summarized as below:(1)The expansion force in solid expandable tubular technology was investigated under different material strengthening models.Based on the twin-shear stress yield theory with the single curve hypothesis,the formulas were derived using three different strengthening models and were verified by the FEM results.The results show that the formulas derived from the ideal elastic-plastic model is unreliable,the linear hardening model and the power exponential hardening model are reliable,and the derivation formula of the power exponential hardening model can fit the true value well,with an error of less than 5%.(2)Taking the finite element programming of the twin-shear stress yield theory as the goal,the tensor expression of the twin-shear stress yield constitutive model is built.According to the UMAT subroutine development interface of ABAQUS software with the Fortran language,the finite element programming of the constitutive model is completed,and it is successfully embedded into the main program of ABAQUS,and the accuracy of the subroutine is verified.(3)The axis axisymmetric FEM model was built by ABAQUS,and the UMAT subroutine was applied to simulate the expandable tubular forming process under different expansion rates.The results show that the stress increases with the increase of expansion rate during the forming process,and the twin-shear equivalent stress contours is distributed in a strip shape.There is a large residual stress after forming,and it increases with the increase of expansion ratio,which indicates that the expansion forming is a non-uniform deformation process.The expansion force increases with the increase of friction factor and expansion ratio,and it is indicates that the friction factor is an effective parameter for controlling the magnitude of the expansion force.In the case of deformation,both the length shortening and the thickness reduction increase with the increase of the expansion ratio,and the growth trend basically increases linearly.The amount of length shortening decreases rapidly with the increase of friction factor,while the thickness reduction increases continuously with the increase of friction factor.Therefore,improving the metal flow performance with increasing the friction factor can reduce the unevenness flow of the metal.(4)The expansion experiment of a TWIP steel expandable tubular with an expansion ratio of 20% was conducted.The results show that after the TWIP steel expandable tubular is expanded and formed,the diameter of the tube is enlarged,the wall thickness is reduced,and the actual expansion rate is 21.02%.The finite element simulation of the same size shows that the actual expansion rate after expansion is 21.33%.The expansion force calculated by the twinshear stress yield theory is closer to the experimental value than that calculated by Mises yield theory,and the relative error is about 2%.The expansion experiment verified the applicability and rationality of the twin-shear stress yield theory applied to TWIP steel materials.