Monitoring of bolt looseness using piezoelectric transducers: Three-dimensional numerical modeling with experimental verification

Across multiple industries, bolted connections have been widely used to hold different parts and components together, due to their advantages such as convenient use and low cost. However, bolt looseness may lead to disastrous consequences if not promptly detected. In this article, a novel numerical modeling is proposed to simulate the piezoelectrically enabled active sensing method that can monitor the looseness of bolted connection, and this investigation can help us better understand the mechanism of the active sensing of a bolted connection. Compared to prior investigations, the main contribution of this article is that we develop a new three-dimensional modeling method on microscopic roughness of bolted interface by using the fractal contact theory. The numerical results, backed by experimental verification from the testing on a bolted joint, reveal that the received signal peak amplitude is proportional to the bolt preload. This phenomenon can be attributed to the enlarging actual contact area with the increasing preload, since a larger contact surface can enhance stress wave propagation. Moreover, the proposed numerical modeling has better performance than similar research in the past, which can provide guidance for future investigations on bolt looseness monitoring.