Local Contact Stiffness Detection for Nondestructive Testing Based on the Contact Resonance of a Piezoelectric Cantilever

In the field of nondestructive testing (NDT), a suitable defect identification parameter plays an important role in evaluating the reliability of structures or materials. In this work, we proposed a NDT method which detects the sample's local contact stiffness (LCS) based on the contact resonance of a piezoelectric cantilever. First, through finite element analysis (FEA) we showed that LCS is quite sensitive to typical defects including debonding, voids, cracks, and inclusions, indicating that LCS could be a good identification parameter. Then, a homemade NDT system containing a piezoelectric cantilever was assembled to detect the sample's LCS by tracking the contact resonance frequency (CRF) of the cantilever-sample system. Testing results indicated that the proposed NDT method could detect the above mentioned defects efficiently and precisely. The cantilever-stiffness dependent detection sensitivity was specially investigated and the stiffer cantilevers were found to be more sensitive to small defects, while the softer cantilevers were more suitable for large defects detecting with smaller pressing force. Finally, the detection limit of this NDT method is investigated both experimentally and computationally. The proposed LCS-based NDT method could be very promising for defect detecting in noncontinuous structures and composite materials.