A method for measuring the dynamic parameters by extracting the incident wave

The complex Young's modulus of viscoelastic materials can be determined by monitoring the propagation of a traveling burst in a thin bar, which is called wave-speed method. While the test samples are always too short to make the incident wave for lower-frequency signals be detected, which lead to low-frequency test is difficult using this method. To solve this problem, a method of extracting the incident wave is presented in this paper. A pulse wave is generated by the exciter and is used to force the longitudinal vibration of a viscoelastic thin bar. The velocities of the two ends of the thin bar are measured by two laser Doppler vibrometers. The incident waves at both of the two ends of the sample can be easily extracted, and the dynamic parameters of the sample can be obtained by the ratio of the vibration velocities of them. This method expands the experimental frequency range of the wave-speed method and the measured results agree well with that of commercial viscoelastic instrument.