Application of Frequency Method for Defining Threaded Joint Tightening Degree

There is a big variety of machines and equipment – internal combustion engines, aviation parts, building frames - joined by threaded joints, realized as bolt, nut and pin ones. For successful and safe exploitation of such equipment, it is required to check the tightening degree of threaded joints. There are few known methods of such control and one is presented in this paper. The proposed method is based on contact stiffness and friction change from thread tightening degree. At the same time, tightening changes with sufficient significance the dynamical properties of such a system - natural and resonance frequencies, amplitude – frequency and amplitude-phase characteristics, so, that it is possible to evaluate the tightening degree of the investigated joint. Dynamic properties are defined by exciting transient process between bolt head and tightened by this bolt detail using as short as possible force impact. Sensors register analogical signal of transient process and transmit it to a special computer card. The computer card converts analogical signal to code. Code is saved in the computer file for further processing. Processing data is saved in this file, and we find desired dynamical characteristics. Using special experimental bench proved that dynamic characteristics are sensitive enough to threaded joint tightening degree and the method is applicable to practice.