fig5

Figure 5. (A) Dependence of output voltage signal on different stresses. The inset shows the linear relationship between the piezoelectric signal and the stress on the sample; (B) Peak Voltage of the collected signals and flexural strain of the specimen during the three-point bending fatigue test; (C) Simultaneously recorded load and capacitance in DCB test, and the capacitance derivative vs. time curve; (D) The nearly linearly relationship between capacitance and the length of interlaminar crack in GFRP laminate.