A bolt preload monitoring method based on the refocusing capability of virtual time reversal

Abstract

Bolted joints are widely used in aerospace and civil structures. Nevertheless, bolts may easily lose preload because of inappropriate initial preloads or time-varying servicing loads. Hence, bolt loosening monitoring is important for ensuring the safety and reliability of the bolt-jointed structures. In this paper, a guided wave method based on virtual time reversal (VTR) and tightness index representing refocusing capability is developed for bolt preload monitoring and to mitigate the requirement of baseline. In VTR, a response signal acquired from the bolted structure in fully tightened condition is reversed and used as the excitation signal for the bolted structure in loosening states. On this basis, the ratio of the energy of the refocused wave packet in final received wave signal to the energy of the entire signal is defined as tightness index (TI E ). In this way, the calculation of TI E does not need to compare with baseline acquired in fully tightened condition. The effects of roughness of contact surfaces on guided wave propagation and the refocusing capability are analyzed by a 2D FE model. The proposed method is also experimentally validated by bolt-jointed structures with single and multiple bolts. The experimental results show that TI E increased almost linearly with the decease of bolt preload and is effective at the early stage of bolt loosening. In addition, the effect of temperature on preload detection accuracy is weak. Furthermore, it is important to select a right frequency to ensure that the TI E is sensitive throughout the entire bolt torque range.

Bolt damage identification based on orientation-aware center point estimation network

“…Wang et al 10 developed a new entropy-based damage index using the multi-scale permutation entropy algorithm, which eliminates the saturation phenomenon of the current damage index and enhances the performance of bolt early looseness monitoring. Du et al 11 proposed a guided wave method based on virtual time reversal and tightness index for bolt preload monitoring. The experimental results showed that the tightness index increased almost linearly as the bolt preload decreased.…”

Percussion‐based bolt looseness identification using vibration‐guided sound reconstruction

“…Mainstream contact methods primarily utilize piezoelectric transducers (PZT) attached to the structures of interest for damage detection. By attaching two PZT patches to each side of bolt joint, 2–5 bolted preload could be discerned by quantifying energy intensity of the stress wave propagating through joint interfaces 6 . Further, a PZT‐integrated smart washer was designed to allow long‐term detection of axial stress changes of fastened bolts 7,8 .…”

A novel autonomous strategy for multi-bolt looseness detection using smart glove and Siamese double-path CapsNet

“…1,2 However, bolted connections are prone to losing sufficient preload, which may result in disasters. Several methods have been proposed to detect bolt looseness, such as acoustic emission method, 3 vision-based methods, 4,5 active sensing method, [6][7][8][9] electromechanical impedance (EMI) method, [10][11][12] vibro-acoustic modulation method, 13,14 vibration-based method, 15 fiber-optic-based method, 16,17 and percussion-based method. [18][19][20][21][22] Though the above approaches have demonstrated promising performance, they all focus on the detection of single-bolt looseness, which is unsuitable for flanges.…”