Using the Subharmonic Resonance to Detect Bolted Joint Looseness

Bolted-joint structures are prone to loosening under vibration, which affect the structural integrity. This paper presents a bolt looseness recognition method based on the subharmonic resonance analysis. The bolted-joint structure is simplified to a nonlinear single-degree-of-freedom (SDOF) model, and the multi-scale method is used to explain the phenomenon of the subharmonic resonance. Experiments are performed on a bolted aluminum beam, where the damage is simulated by loosening the bolts. Two surface-bonded piezoelectric transducers are used to generate continuous sinusoidal excitation and receive corresponding wave signals. The experimental results demonstrate subharmonic components would appear in the response spectrum when subjected to the excitation of twice the natural frequency, which can be effective on bolt looseness damage detection.