Nonlinear Analysis of the Threaded Connection with Three-Dimensional Finite Element Model

摘要

The engagement surface of the threaded connection of Oil Country Tubular Goods (OCTG) is a complex helical surface.The stress analysis of the threaded connection involves material nonlinearity,geometric nonlinearity and contact nonlinearity.It is difficult to obtain an analytical solution and the finite element method (FEM) is a powerful numerical method for solving the problem of threaded connection.Due to the complexity of three-dimensional modeling and the difficulty of computational convergence,researchers usually use two-dimensional axisymmetric finite element models to analyze the characteristic of threaded connection.However,two-dimensional axisymmetric model can not efficiently simulate the stress characteristics of the threaded connection with make-up torque,which has greatly influence on the reliability of the connection,and it can not reflect the real stress state of the threaded connection.In this paper,an explicit dynamic FEM is employed and the nonlinear contact theory,nonlinear elastic-plastic stress-strain relationships and the von Mises yield criterion are considered to analyze the stress distribution of the threaded connection.As examples,three-dimensional elasto-plastic finite element models of bypass valve and drill pipe threaded connection are established.Mechanical characteristics of the threaded connections are analyzed,in which the make-up torque,axial loads and working torque are comparable with the real working conditions.It is found that the pin of bypass valve threaded connection shows a high stress and is broken when the working torque exceeds 22992.8 N·m.Meanwhile,drill pipe threaded connection is reliable under the most demanding load.Analysis results presented in this paper are consistent with the field observation.