“…Although many academic works have explored different methods of detecting bolt loosening, including vibration-based measurements [ 2 , 3 ], electro-mechanical impedance methods [ 4 , 5 , 6 , 7 , 8 ], electrical conductivity techniques [ 9 ], ultrasonic-based measurements [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ], and vision-based methods [ 21 , 22 , 23 , 24 , 25 , 26 ], much less research has been done on the applications of machine learning (ML) or deep learning (DL) algorithms in this field. Recently, ML and DL have become the breakthrough tools, particularly in the field of computer vision, to overcome the limitations of conventional structural health monitoring (SHM) and non-destructive evaluation (NDE).…”