Full-Field Vibration Measurement by Time-Average Speckle Interferometry and by Doppler Vibrometry - A Comparison

摘要

Identification of dynamic material properties, non-destructive testing and study of vibroacoustic behaviour of different structures require the use of complex, pointwise and full-field measurements, which are capable of providing data for experimental modal analysis or model updating. Nowadays, among other techniques, optical non-contact techniques represent the favourite choice as they do not add mass, stiffness or damping to the structure under test. When the range of vibration amplitudes allows it, most of these techniques are based on interferometric principles. Development of laser sources and detectors leads to a continuous improvement of vibration measurement techniques. However, a hard choice still has to be made between spatial resolution and temporal resolution. Another difficult choice is between space bandwidth product and energetic sensitivity of the detector. While the number of pixels of a camera is continuously increasing, the pixel size seems limited at its lower end. The paper presents a comparative study of the vibration amplitude fields as measured by two full-field non-contact techniques, speckle interferometry and laser Doppler vibrometry, and predicted by finite-element model. The measurements concern the free and the forced vibrations of a thick, composite plate with free boundaries.