Integrated acoustic‐vibration frequency‐modulation technology to detect the contact nonlinear features of mechanical structure

Bolt connection is mostly used to transfer the load between the mechanical components and plays a significant role in fixing and connecting the parts, especially in complex engineering structures. About 20% of mechanical system failure cases are related to bolt looseness; hence, timely bolt condition detection and maintenance can extend the working life of the mechanical system. To this purpose, current research proposes an integrated approach that significantly simplifies the test system in the conventional method and facilitates the online monitoring of bolted state, especially for small size and compact measured components. Using the proposed integrated acoustic‐vibration frequency‐modulation (FM) method, the signal characteristics are analyzed in the frequency domain to find out the frequency components associated with bolt looseness. Further, the proposed method is also experimentally verified by applying it to examine the specimen containing fatigue cracks, and the damage characteristics are obtained without a reference signal. In this framework, the proposed method is found to be more convenient and flexible than the traditional FM technology in the application of contact nonlinear condition monitoring.