Measurement of rotating beam vibration using optical (DIC) techniques

In this paper, an experimental study is presented to validate a dynamic model of a rotating beam. The majority of existing vibration instrumentation is typically wired to an acquisition system through a connection using slip rings. An issue is the inherent signal to noise and the reliability of slip ring electrical connections. Herein, an experimental test rig is designed to overcome these issues. In addition, the rig is conceived to incorporate capabilities such as applying variable rotational speed using a variable frequency driver and provide vertical base excitation input to the centre of the rotation using a linear bearing. The tests are performed using random excitation on the fixed end of the rotating cantilever beam to excite the flapwise modes of the beam. The responses are then measured optically using a single high-speed camera, and the images are post-processed using a digital image correlation (DIC) method. This non-contacting optical method is used to extract the deflection of the beam as a function of time. The frequency response functions are then obtained from the measured responses. The modal frequencies are estimated and compared with numerical simulations to validate a Rayleigh-Ritz and FE numerical model for different rotational speeds.