Theoretical and Experimental Identification of Clearance Nonlinearities for a Continuum Structure

Clearance is unavoidable in many engineering structures due to the manufacturing and installation errors. These clearances can cause intense impact and wear of the contacting pairs, which may change the dynamic response and eventually reduce the movement precision and the service life of the transmission system. Parameters identification of the clearance would provide better understanding of dynamic behaviors of the clearance and contribute significantly for the control of the induced disturbance and deviation. In this paper, based on dynamic characteristics of the clearance nonlinearity, the piecewise fitting method is first proposed to identify the clearance value of the continuum structure. During the proposed method, first, the rough scope of the clearance value extracted from the displacement response is divided into subintervals. And then, the nonlinear force is fitted by the piecewise linear function in the subintervals. Once the equivalent stiffness is obtained, the clearance value can be calculated by the sorting nonlinear force–displacement curve. The feasibility of the piecewise fitting method was verified by a cantilever beam system with clearances in simulation. Besides, some influence factors of this identification method, including the clearance value, exciting force level and measurement noise, are fully discussed to illustrate the robustness of this method. Moreover, an experiment system of a cantilever beam with adjustable clearances was designed to experimentally validate the effectiveness of the proposed method, and the results show that the piecewise fitting method can precisely identify the clearance value of continuous systems.