Numerical analysis of load capacity and strength of rigid flanged shaft couplings

Abstract

Rigid flanged shaft couplings are commonly used to connect two shafts that transmit large torque. A pair of flanges is clamped by multiple reamer bolts since they are subjected to large shear force. In JIS B 1451, it is assumed that the shaft torque delivered to shaft couplings is transmitted only through the cylindrical surface of reamer bolt as shear forces, although it is also supported by the friction force on the contact surfaces. In the previous paper, Shear Force Transfer Ratio (SFTR) is defined in order to evaluate the ratio of the shear forces supported by the reamer surface and the action of friction. Then, the distributions of SFTR and the bending stresses along the reamer surface are analyzed by three-dimensional FEM, focusing on the effect of the fit between the cylindrical surface of reamer bolt and the bolt hole. In the actual rigid flanged shaft couplings, it is predicted that the scatter of initial bolt stress among multiple bolts and the misalignment between the two shafts significantly affect the SFTR and the bending stresses to be produced. Commonly observed misalignments are parallel misalignment or offset, axial misalignment or endplay, and angular misalignment. In this study, the effects of the scatter of initial bolt stress and the misalignments listed above are analyzed by three-dimensional FEM, in which an engaged thread portion with complex geometry is replaced by a simple cylinder. By conducting parametric calculations, it is concluded that the bolt force scatter has a minor effect under the commonly encountered tightening conditions, and the angular misalignment specifically affects the load capacity and the bending stresses generated in reamer bolts. It is also found that unlike the other types of misalignments, a harmful influence of angular misalignment cannot be mitigated even if the initial bolt stress is increased.