Attenuation of Lamb Waves in CFRP Plates

The paper presents the Lamb wave attenuation of Carbon Fiber Reinforced Plastic (CFRP) plates on the basis of an experimental transmitter-sensor scheme. We measured separately the S0 and A0 Lamb modes of CFRP plates with three different kind of laminate lay-ups; unidirectional [0]8s (and [90]8s), cross-ply [0, 90]4s, and quasi-isotropic [0,45,-45,90]2s. Several ultrasound transmitters were used as actuator and short-duration high-voltage pulses were used for excitation. Two kinds of AE resonant sensors with resonance frequency around 260 and 500 kHz, respectively, were used to record the Lamb waveforms of the plates. By using sensors on both sides of the plate, the confirmation and separation of both modes, S0 and A0, were successfully carried out. This result was also confirmed by using the wavelet transform of the recorded signals. The experiment was carried out at several transmitter-sensor distances, so both phase and group velocities and attenuation could be obtained. By means an appropriate fitting of a theoretical model of attenuation, including the geometrical attenuation, the damping factor of both modes was obtained for each laminate and sensing frequency. The experimental results for velocities and damping factors were compared with previously published and theoretical ones. Directivity results are also reported, showing complex behavior dependent on laminate layups as expected.