Measuring plate vibration using deflectometry: The advantages and limitations of add-on reflective material

Deflectometry is a full field optical method which utilizes the slope fields on the surface of a planar object to track deformations. The use of a high speed camera gives the ability to measure all points on the surface instantaneously and with high spatial resolution, providing more knowledge on how structures react to transient excitations. Here, the reflected grid method will be used, as it involves geometry that allows for simple calculation of curvature distributions. This method of deflectometry relies on specular reflections to create amplifications of the measured deformations in the test plate. Therefore, this requires the plate under test to have a reflective surface. An experiment was constructed to test the vibration of a flat plate excited by an automatic force hammer. A collection of adhesive tapes, films, and spray were applied to the test object in order to increase the reflectivity of the plate. The advantages and limitations of each type of add-on reflective material will be discussed. Finally, the add-on material was used on a more complex structure to showcase the potential of deflectometry for measuring plate vibration.