Abstract:
Structural intensity is the energy flow of elastic waves through mechanical structures. In this work, the use of piezoceramic strain sensors for estimating the structural intensity of flexural waves propagating in beams at high frequencies is presented. The work was intended for structural health monitoring applications. A beam's dynamic response was modelled using the Timoshenko beam theory, which shows that above a certain cut-on frequency, a second type of flexural wave propagates. The method for estimating structural intensity was formulated based on average surface strain measurements. At above the cut on frequency, the two types of waves present were distinguished by analysing the different compositions of their structural intensity components. Three excitation cases of different frequency bands were studied: below, above and overlapping the cut-on frequency. Simulations showed that in all three cases, the structural intensity could be estimated in the time domain using digital filters. In particular, infinite impulse response filters were implemented for the excitation band overlapping the cut-on frequency. Experimentally, the intensity estimation method using piezoceramic strain sensor inputs was compared with those obtained using transverse velocity inputs measured by a laser vibrometer. At excitations below the cut-on frequency, both transducers were able to give structural intensity estimates to correctly identify the incident wave, however the reflected wave was only identified correctly by the strain sensors. In the case of excitation bands overlapping the cut-on frequency, only the strain sensors yielded structural intensity estimations consistent with the Timoshenko model. It was found that the laser vibrometer's measurements had a high level of noise contamination. At excitation bands above the cut-on frequency, the high frequencies of excitation caused the beam's behaviour to deviate from that predicted by the Timoshenko model.
