Enhancement of fatigue life of net section in fitted bolt connections

Abstract

The basic idea of this paper underscores enhancement of fatigue life of the net section in bolted connections by means of the developed method whereby beneficial residual hoop compressive stresses, distributed almost uniformly along the hole axis, are created around the bolt hole. Since the method includes bolt hole cutting up to a precise size after preliminarily cold hole expansion, it is especially appropriate for fitted bolt connections. In the case of conventional cold hole expansion the residual compressive hoop stresses are characterized by significant axial gradient and a tensile field sometimes arises on the hole entrance face. The proposed method homogenizes the compressive field around the bolt hole in an axial direction by means of residual hoop stress redistribution. These stresses significantly reduce the operating tensile stresses at the net section points. Due to the tensile operating load, the resultant hoop normal stresses (superposition from residual compressive and operating tensile stresses) at the net section points are significantly smaller in comparison with the conventional case. The developed method has been studied both experimentally, by X-ray diffraction technique, and numerically, by finite element (FE) simulations. Four FE models have been developed for investigation and optimization of the proposed approach. Application of this approach enhances the fatigue life of the net section in bolted connections due to operating tensile stress reduction.