عنوان مقاله [English]
In this article using axisymetric elements in ANSYS standard code, threaded tool joints of drill strings, which expose to failure in vertical drilling more than other members, have been modeled. Also, for modeling the contact between surfaces contact elements are used. Axial tensile and compressive forces, internal and external pressures arising from drill fluid on pipe, exerted torque by the motor on the top of the well, and bending moment caused by drill collars buckling are the main loads exerted to the model. According to the API standard, some preloads are also exerted to the tool joint to improve the fatigue behavior. Different types of loading composed of tension and compression, pure preload and combination of them are applied to the model. Some conclusive results have been drawn from the analysis including the location and value of maximum stress concentration factor in Pin and Box, the effect of preload on the stress concentration factor and as a result on the fatigue life of the tool joint and the contact stress distribution on the screw threads. Finally, convergence of the contact pressure on the contact surfaces has been investigated.