Three-dimensional parametric modeling and mechanical characteristic analysis of S135 drill pipe joint thread
S135 steel drill pipe has been widely used in drilling construction such as mine exploration,water exploration and gas extraction.However,due to the cyclic effects of axial tension,compression,torsion,bending,and their composite loads on the threads of drill pipe joints,the service life of the joint threads is far lower than their design life,making them the weakest link in the entire drill pipe struc-ture.Therefore,the mechanical properties of drill pipe joint material were obtained by tensile test,and its constitutive parameters were calculated and transformed to obtain the finite element analysis of the drill pipe joint.In order to improve the efficiency of finite element analysis,the geometric expression of the thread section profile perpendicular to the axis of the drill pipe joint was derived.Based on the de-sign ideas of rotation,lifting,reduction radius and connection nodes,a three-dimensional thread para-metric modeling method considering the taper and shoulder of drill pipe joint was proposed.Based on the relationship between elements and nodes,a parametric 3 D hexahedral mesh modeling program for drill pipe joint connection was developed,and its validity and feasibility were verified by comparing with the calculation results of interactive modeling method.Furthermore,mechanical characteristics of the joint external thread under the combined load of make-up torque,compression and torque,com-pression and torque and bending were analyzed.The analysis results indicate that:The stress on the ex-ternal thread of the drill pipe joint under three working conditions shows an approximate"bathtub"shape,with the maximum stress on the first tooth.With the increase of the number of turns,the stress on the thread teeth decreases rapidly,and the stress on the last round of thread teeth shows an upward trend.Under the action of bending moment,the stress on the thread teeth exhibits asymmetric charac-teristics.When designing joint threads,it is necessary to consider the influence of wellbore curvature and pay special attention to the stress on the first thread tooth of the compression edge of the joint.
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