Laser vibrometry to identify resonances of coated substrates

摘要

It is often desirable to determine the resonant frequencies of complex bodies, either to avoid vibrations (such as in car design) or to enhance them for a specific application. Under some circumstances, the body may be fragile or unstable, such that conventional methods of analysis are inappropriate. Laser vibrometry offers a method of analysing very small displacements or surface velocities (μm or smaller) which is non-contact and thus does not alter the mechanical properties of the object. This is particularly useful when investigating the behaviour of objects covered in layers of a delicate coating. This paper presents a method of establishing not only the resonant frequencies, but the displacements caused by each resonance using a scanning laser vibrometer. Analogies are drawn to equivalent numerical methods of Eigen analysis, as well as impedance analyses, showing how the three methods are complimentary. The work illustrates how oscillating an object at different frequencies causes dramatically displacement patterns, which can be predicted by numerical modelling methods and then validated experimentally with two independent analyses.