Application of finite element method in the structure optimization of drill collar thread

The bottom hole assembly failure caused by drill collar thread usually occurs during the air drilling. On the basis of field resources analysis, the drill collar thread model is created by UG, and analyzed the thread stress under different axial forces by finite element method. The structure optimization design process of drill collar is described in the paper. It is summarized that R1=8 mm, R2=15 mm is the optimum transition radius of stress relief groove.