Electromechanical impedance method for assessment of adhesive bonds of CFRP at the production and repair stage

Numerous techniques of non-destructive testing (NDT) of structural parts of CFRP are investigated. In this paper electromechanical impedance (EMI) technique is studied as an NDT tool for assessment of adhesive bonds. In order to perform the assessment a surface mounted piezoelectric sensor is used. Due to the piezoelectric effects the electrical response of the sensor is related to mechanical response of the inspected object. The electrical quantities of the sensor are tracked in order to find a relation with the mechanical state of the object. In the reported research adhesively bonded CFRP samples were investigated. The adhesive bonds were modified simulating the conditions in manufacturing and repair stages. Sample surface was contaminated before bonding with release agent in order to simulate a manufacturing stage threat to the quality of the bond. Pre-bond thermal treatment, pre-bond contamination with de-icing fluid, and faulty curing of the adhesive were considered as repair stage threats to the quality of the bond. The electromechanical impedance spectra were investigated searching for anomalies and changes caused by modification of the adhesive bond. These spectra for different cases were compared with reference measurement results gathered from pristine samples. Numerical indexes for comparison of the EMI characteristics were proposed. The sensitivity of the EMI method to modified bonds was observed