AbstractsEngineering

Acoustic Emission (AE) based structural health monitoring systems have the potential to assess the state of metallic / composite structures and detect damage in real time as it grows. This is done by monitoring the Lamb waves that occur due to the release of energy and the specific boundary conditions. Environmental and Operational Conditions (EOC) have a significant effect on the wave propagation phenomena, potentially influencing their ability to detect and localize damage. This study sought to extend past research done on metallic structures and was focused on understanding the effects of temperature on the propagation of ultrasonic Lamb waves in composite materials using analytical, numerical and experimental tools. Two test specimens were used, one hybrid laminate with glass and carbon fibre epoxy layers and a sandwich panel with a 2 mm foam. Three temperatures steps of -40, 25 and 70°C were used. An analytical MATLAB code was used to generate dispersion curves for the hybrid material at the previously mentioned temperature steps. Next, the experimental setups were modeled in an FEM ABAQUS CAE environment. Three 5 cycle Hanning windows, with frequencies of 150, 300 and 400 kHz, were used to excite a piezoelectric actuator. The response was then picked up using 3 piezoelectric sensors located at angles of 0, 45 and 90° with respect to the actuator. Finally, the experimental tests were performed and the results were compared with those of the FEM model and the dispersion curves. The comparison was performed using the signals received by the 3 sensors. Preliminary experimental results showed that the maximum change in speed due to temperature variation was 7% for the laminate and 12% for the sandwich panel. The results have also been verified using the FE models.