Abstract
The aim of this study is to design and test a new, simple, and reusable linear variable differential transformer (LVDT)-based in situ bolt preload monitoring system (L-PMS) during fastening of a truck wheel assembly. Instead of measuring the elongation of a bolt, the distance between the end surfaces of both the bolt and nut was monitored via the L-PMS. The distance obtained from the L-PMS was experimentally correlated with the actual preload measured by a washer-type load cell. Since the variation of the distance is related to the stiffness of the bolt and clamped parts, a finite element analysis was also conducted to predict the sensitivity of L-PMS. There was a strong linear relationship between the distance and bolt preload after the bolt and nut were fully snugged. However, a logarithm-shaped nonlinear relationship was irregularly observed before getting snugged, making it difficult to define a clear relationship. In order to tackle this issue, an arc-shaped conductive line was screen-printed onto the surface of the clamped parts using a conductive carbon paste. The results show that a resistance variation of the conductive line during fastening enables to determine the snug point, so the L-PMS combined with resistance measurement results in an approximately ±6% error in the measurement of bolt preload. The proposed L-PMS offers a simple but highly reliable way for measuring bolt preload during fastening, which could be utilized in a heavy-truck production line.
Highlights
IntroductionBolts have been widely used for assembling machine components owing to the associated easy-tightening process and their relative insensitivity to service temperature and humidity
Bolts have been widely used for assembling machine components owing to the associated easy-tightening process and their relative insensitivity to service temperature and humidity.Bolted joints play important roles in maintaining structural integrity since their failure could lead to a catastrophic result
Initial nonlinear relationships between Dbn and the preload were found before reaching to the snug point, which hinders a reliable estimation of the preload using the L-PMS
Summary
Bolts have been widely used for assembling machine components owing to the associated easy-tightening process and their relative insensitivity to service temperature and humidity. Bolted joints play important roles in maintaining structural integrity since their failure could lead to a catastrophic result. Bolts have often been considered one of the most neglected mechanical elements in engineering design of machines and structures. To improve the reliability and durability of machine parts, bolts must be properly tightened to pre-specified values of preload. Structural bolted joints are increasingly garnering attention in the automotive industry because of failure of bolts under harsh conditions and noise problems such as buzz, squeak and rattle due to insufficient preload [4]. Tens or hundreds (or even thousands) of bolts are Metals 2019, 9, 336; doi:10.3390/met9030336 www.mdpi.com/journal/metals
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