Design research on the unmeshed thread section structure of engine conrod bolts

Abstract

In the design standard for hexagonal flange bolts, the reliability of the bolt connection structure varies when different structural forms of bolts are selected. However, there are few studies on the design and selection of bolts with different structural forms, and the design law of the bolt connection structure cannot be summarized comprehensively. In this paper, a finite element model of conrod bolt tightening was established based on the mesh convergence criterion, and the model was verified by comparing the simulation curve of tightening torque-bolt preload with the theoretical curve. The influence of the length of unmeshed thread, the length of thin rod and the diameter of thin rod section on the stress and deformation of conrod bolt was studied, it is found that the increase of the three kinds of structural parameters will reduce the stress concentration and radial deformation at the first thread of engagement, which can guarantee the structural strength of the bolt. At the same time, the fatigue safety factor of the bolt easy-to-failure region was analyzed, and the reliability of different structural forms of bolts was evaluated comprehensively. The results show that when the structure of bolt conforms to the design standard of full thread hexagonal flange bolt, the length of unmeshed thread is 27 mm, the stress value and radial deformation of the first thread are the smallest, and the fatigue safety factor of the bolt easy-to-failure region is the largest, which is not easy to damage. In the design of hexagonal flange bolts, full thread hexagonal flange bolts are used as much as possible.