Fabrication of PVDF film sensors for fatigue damage monitoring of single-lap adhesive joints

Polyvinylidene fluoride (PVDF) has been widely used in piezoelectric applications because of its outstanding properties such as low permittivity, high thermal stability, high chemical resistance, and flexibility. In this study, PVDF film sensors were prepared for fatigue damage monitoring of single-lap adhesive joints. PVDF films were fabricated using the solvent casting method, and post treatment, including mechanical stretching and heat setting, was conducted to increase the β-phase crystallinity of the films. Subsequently, the PVDF films were polarized to align the molecular dipoles. The crystal structures of the PVDF films were investigated using X-ray diffraction (XRD) and the thermal behaviors were analyzed using differential scanning calorimetry (DSC). The piezoelectric constants of the prepared PVDF films were measured using a d33 meter. The sensing performance of the films for fatigue damage monitoring of single-lap adhesive joints was assessed by fatigue tests under various stress levels. In addition, a fatigue failure manual based on the PVDF sensor signal, which can predict the failure of the adhesive joints, was constructed.