The reflected wave is a tensile pulse, which interacts with internal interfaces and can cause actuator fracture, delamination and debonding depending on its amplitude. The incident pressure pulse produces a piezo voltage in the piezoceramic plate of the specimen. The pressure wave reflected at the transmission bar loads the specimen as tension wave. Interpretation of piezo voltage behaviour is most complicated due to wave interference. Figure 6 shows some results of a prepreg laminate.
Top diagrams present the piezo voltage during three shots.
These slopes may be caused by local actuator breaking. Furthermore, a dark circle is formed in the middle corresponding to the incident bar. The metal coating is damaged due to actuator cracking. Starting from this circle, radial cracks are spreading. The smooth form is lost, the peaks are lower.