Measurement of the isotropic dynamic Young's modulus in a seismically excited cantilever beam using a laser sensor

An approach to the direct measurement of the dynamic Young's modulus for a viscoelastic material using a contactless sensor, based on a laser emitter-receiver, is presented in this paper. The proposed method consists in exciting a cantilever beam specimen by means of a seismic acceleration. The acceleration of the base is recorded by means of a piezoelectric accelerometer, and the vertical displacement of a suitable point of the specimen is recorded by means of an accurate laser sensor. Using a contactless sensor avoids introducing any perturbation due to contact that could locally change the mechanical properties of the material. This enables one to accurately determine Young's modulus as a function of frequency. A mathematically accurate treatment of the experimental measurement of Young's modulus is also presented, yielding a final expression for E(i omega) as a function of the two measured entities, namely the acceleration of the base and the vertical displacement of an adequate point of the specimen. Experimental curves of Young's modulus at different temperatures are reported. (C) 2000 Academic Press.