Design of a networking bolted joints monitoring method based on PZT

As the failure of bolt connections by corrosion can result in major disasters and cause casualties and property damage, monitoring bolted joints is of great importance. However, current researches on lamb wave based bolted joint monitoring mainly focused on single-input-single-output (SISO) systems, which require a long diagnosis time and numerous transducers. To reduce the number of transducers on monitoring, the multiple-input systems, i.e. multiple-input-multiple-output (MIMO) system and multiple-input-single-output (MISO) system, can be adopted. However, both multiple-input systems are prone to failure due to the interference among the excited waves generated from multiple simultaneously-operated actuators. To remove such interference, an orthogonal variable spreading factor (OVSF) code based bolted joint monitoring method is proposed here. Firstly, instead of using the same detection signal, multiple detection signals generated using OVSF codes are emitted from different input ports. Then, for each considered input port, the corrosion information carrying waveforms are recovered from the acquired signals via timing acquisition and demodulation and utilized to reveal the status of the bolted joints via wavelet packet based analysis. To validate the proposed method, experiments with a MIMO system (i.e. three-input-two-output system) and a MISO system (i.e. six-input-single-output system) were conducted to simultaneously reveal six given bolted joint corrosion status in this research. Since the proposed method effectively suppresses the interference, the MIMO/MISO bolted joint monitoring system can present a performance similar to that of the SISO monitoring system but require fewer transducers.