Influence of repair-related modification of adhesive bonds on electromechanical impedance characteristics

There is a continuous search of non-destructive testing (NDT) techniques dedicated to assessment of adhesive bonds. In this research we focus on adhesive bonds of composite parts made of carbon fibre reinforced polymers (CFRP). The electromechanical impedance (EMI) technique was proposed. The technique uses a piezoelectric sensor that is surface mounted on the inspected structure. The electrical quantities of the sensor are measured as a function of frequency. Due to direct and converse piezoelectric effects the electrical response of the sensor is related to mechanical response of the structure. Analysing changes in conductance, resistance and other quantities one draws conclusion about the mechanical state of the structure. In the reported research adhesively bonded CFRP samples were investigated. Each sample comprised of two CFRP plates joint by the adhesive. Pre-bonds modification of the plates were investigated. The modification comprised of sample treatment (for example: thermal treatment) or contamination (for example with release agent).The paper shows results of EMI technique for single pre-bond modifications as well as mixed modifications of two types. Differences between the cases are discussed