Investigation of the zero-crossing technique in measurement of phase velocities of the guided wave in thin CFRP composite plate
Keywords:Lamb wave, mode, dispersion curves, phase velocity, zero-crossing technique, non-homogeneous material.
AbstractOne of the main areas for application of the guided waves is inspection of composite materials. These materials usually possess anisotropy of elastic properties. In order to investigate the possibilities of the developed phase velocity measurement technique based on accurate measurements of the zero crossing points of ultrasonic signals the numerical modelling of a thin CFRP plate was carried out. The finite element model of the CFRP plate with thickness 0.2 mm, length 100 mm and width 40 mm was created and used in order to obtain the signals for analysis. The A0 mode was excited by attaching tangential force and the S0mode by attaching normal force to the one edge of the plate. The width of the excitation zone was 10 mm and it was situated in the center of the plate. The waveform of the excitation signal was 3 period, 400 kHz burst with the Gaussian envelope. In general, the investigations demonstrated the same regularities as were obtained on non-homogeneous material and enable to identify different modes in the signals and to reconstruct the segment of the phase velocity dispersion curve.
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