ABSTRACT
The resonance method is based on the excitation of a test specimen by a certain external frequency (the resonance frequency) in its natural oscillations. Depending on the type of excitation, one obtains longitudinal, torsional or bending vibrations. The resonance frequency is dependent on the geometrical dimensions, mass distribution and elastic properties of the specimen. In general, the specimens should have a simple geometrical shape. Prisms or cylinders are suited best if their length is four to six times their cross dimensions. The excitation is induced by a large band, adjustable electrodynamic emitter. When the exciting frequency equals the natural frequency of the specimens, “standing waves” are produced, that is to say, resonance occurs. The amplitude of the resulting oscillations reaches a maximum. Since the natural frequency of a specimen is largely dependent on the elastic properties of the materials to be tested, conclusions can also be drawn concerning its elastic constants.
