APPLICATION OF LASER VIBROMETRY AND A RESONANCE TECHNIQUE TO THE MEASUREMENT OF THE COMPLEX MODULUS OF ELASTOMERIC MATERIALS

摘要

An optical technique is described for obtaining the dynamic loss factor and Young's modulus of elastomeric materials. The technique involves a two channel laser Doppler vibrometer for measuring the relative amplitude and phase at two points on a longitudinally excited material sample. Replacing the two accelerometers ordinarily used in this materials characterization technique with non-intrusive laser probes offers numerous advantages. The primary advantage is the simplification of the mathematical procedure for obtaining the material properties since end mass (accelerometer) effects can be discarded. Results from a test conducted to compare optical and accelerometer data show very good agreement except at frequencies where the sample and/or test apparatus exhibit a high degree of flexural motion. The lack of agreement in these cases is explained. In such cases it is recommended that the optics be rotated in order to detect these flexural modes so that they can be avoided, if warranted, when evaluating the longitudinal response of the sample.