Impact Damage Detection in Composite Laminates Using PVDF and PZT Sensor Signals

Low-velocity impact damage is a major concern in the design of structures made of composite materials, because impact damage is hidden and cannot be detected by visual inspection. Piezoelectric sensors can be used to detect variations in structural and material properties for structural health monitoring. In this study, polyvinylidene flouride (PVDF) and lead zirconate titanate (PZT) sensors are used for monitoring impact damage initiation and propagation in composite laminates to illustrate this potential benefit. Several tests for monitoring the stress wave signals including acoustic emission due to failure modes, such as matrix cracking, delamination, and fiber breakage are performed. A series of impact tests at various impact energies by changing the impact mass and height is performed on the instrumented drop weight impact tester. The wavelet transform (WT) and short time fourier transform (STFT) are used to decompose the piezoelectric sensor signals in this study. Test results show that the particular waveform of sensor signals implying the damage initiation and propagation are detected above the damage initiation impact energy. It is found that both PZT and PVDF sensors can be used to detect the impact damage.