Air coupled Lamb waves evaluation of the long-term thermo-oxidative ageing of carbon-epoxy plates

Thermo-oxidative ageing of carbon-epoxy plates has been done for up to 3500 h at two temperatures. Non-destructive evaluation by means of non-contact ultrasonic methods has been tested to characterize the aged plates. Experimental results obtained using Lamb waves propagation in the plates are presented here. Experimental and theoretical dispersion curves are compared. It is shown that the phase velocity of the A0 and S0 Lamb modes is decreasing when ageing duration increases. Assuming the plate to be homogeneous and orthotropic, we demonstrate that this phenomenon is related to an important decrease of the C55 elastic parameter of the plate.