Residual torque–preload correlation in bolted joints and its application to reducing preload dispersion

초록

Batch tightening of bolts to a specific torque inevitably leads to preload dispersion, which can affect structural integrity. Residual torque is commonly used to detect such dispersion, based on the assumption that higher residual torque indicates higher preload. It is generally measured using on-torque and off-torque methods, applied in the bolt tightening and loosening directions, respectively. However, these methods have limitations, as the actual correlation between residual torque and preload in batch-tightened bolts remains unclear. To address this issue, we experimentally investigated the correlation under different tightening conditions. Furthermore, finite element analysis (FEA) was performed to assess bolt stress distribution after residual torque measurement. Contrary to the commonly assumed positive correlation, our results revealed a negative correlation between both types of residual torque and preload, with a more evident and stable negative correlation observed for off-torque. The FEA results showed that on-torque measurement caused progression of plastic deformation, whereas off-torque measurement reduced it. Finally, leveraging the negative correlation, a novel tightening method based on off-torque was developed. This method reduced the standard deviation of preload by 37% compared to conventional torque tightening, without affecting average preload. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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