Practical Experiences to Know Making Acoustic Emission-Based SHM Successful

The use of ultrasonic waves in the context of SHM offers methods to analyze materials and systems. Both Acoustic Emission-based approaches (passive, active) are limited by the propagation characteristics of ultrasonic waves, especially in inhomogeneous materials like carbon fiber reinforced polymers (CFRP). The use of the piezoelectric and inverse piezoelectric effect is a very accurate method of sensing and exciting ultrasonic waves. However, the transducers resonance characteristics affect the waveforms. For illustration in this contribution different excitation signals are experimentally compared in frequency domain by fast Fourier transform (FFT) and in time-frequency domain by continuous wavelet transform (CWT). Then transducers effects along the propagation path of the wave are investigated. Frequency and fiber direction dependent damping factors of ultrasonic waves in CFRP as well as the influence of the transducers are determined. The distance between sensors in a sensor network is limited by attenuation, so fiber direction must be considered. Finally, by analyzing the frequency response of the transducer, a filtering method is developed to compensate for the resonance characteristics of the transducers. Finally, a more accurate estimate of the energy released and therefore a more accurate estimate of the severity of damages/failures is proposed.