An analytically improved four-stage model for single-lap torqued bolted joints accounting for preload relaxation. (January 2023)

• Record Type: Journal Article
• Authors: Liang, Yichen; Xu, Fei; Zhang, Xiaoyu; Wang, Anwen; Ma, Chunhao
• Is Part Of: Thin-walled structures. Volume 182(2023)Part B
• Publication Date: 2023-01
• Subjects: Preload relaxation -- Bolted joint -- Composite connection -- Poisson's effect -- Theoretical model; Thin-walled structures -- Periodicals; 690.1
• DOI: 10.1016/j.tws.2022.110252
• Languages: English
• ISSNs: 0263-8231

Abstract

Abstract: The bolted joint is a vital connection type in aerospace, shipping, mechanics, and other fields. The bolt preload always exists and is standardly specified due to the tightening of the bolts, which would significantly influence the joint's mechanical properties because of the preload relaxation. However, the vast majority of extant theoretical models of bolt joints do not account for this influence. In this study, the mechanism of preload relaxation in a single-lap bolted joint subjected to static tension is investigated. An improved analytical four-stage model is then proposed, which can predict the load–displacement curves of bolted joints with the preload relaxation for various initial bolt preloads, bolt-hole clearances, and materials with varying component thicknesses. The load–displacement curves predicted by the improved four-stage model demonstrate that due to preload relaxation, the slope of the joint load–displacement curve decreases in the first, second, and fourth stages, and the turning points of each stage would be moved back accordingly. The improved model enables the structural engineers to precisely determine the effects of various sensitivity factors on the bolted joint. The results indicate that a higher initial bolt preload, a thinner joint, and the combination of high stiffness bolts and low stiffness plates would result in a more pronounced preload relaxation. Highlights: The bolt preload would relax under static load, reducing the joint stiffness by more than 50%. An improved four-stage model was derived to account for the bolt preload relaxation. A sensitivity analysis is conducted to show the effect of the elastic modulus of the bolt/plate on the preload relaxation. It is demonstrated that preload relaxation is more significant for thin-walled structures with small-spacing bolts.