Oberst Beam Excitation Using Piezo Electric Actuators
AbstractThe «Oberst beam» is a classical method for the characterization of damping material based on a multilayer cantilever beam (base beam + one or two layers of other materials). As the base beam is made of a rigid and lightly damped material (steel, aluminum), the most critical aspect of this method is to properly excite the beam without adding weight or damping. So, exciting the beam with a shaker is not recommended because of the added mass. Alternative solutions are suggested such as electro-magnetic noncontacting transducer (tachometer pick-up, for example) can provide a good excitation but it is limited to ferro-magnetic materials. As aluminum and stainless-steel are widely used for the base beam, a small bits of magnetic material must be fastened adhesively to achieve specimen excitation. This method creates two other problems. The first one is the difficulty to properly measure the excitation force and the second one is the added damping due to the magnetic materials bits in the case of non-magnetic base beam. However, the measurement of the motion of the beam can be easily made using a non-contact transducer (a laser vibrometer for example).
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