Electrochemical impedance spectroscopy inspection of composite adhesive joints

Abstract

Lap shear joints comprised of aluminum-aluminum, aluminum-glass fiber-reinforced polymer (GFRP), aluminum-carbon fiber-reinforced polymer (CFRP), CFRP-CFRP, CFRP-GFRP and GFRP-GFRP, were exposed to 95% relative humidity (RH) at 50 • C, 70 • C and 90 • C, to salt fog and to a 90 • C/95%RH freeze cycle. Electrochemical impedance spectroscopy (EIS) spectra were taken across the whole bonded assembly using an EIS corrosion sensor. Periodically, some specimens were pulled to obtain bond strength as a function of exposure. As expected, the higher the temperature, the faster the bond degradation. The low-frequency impedance correlated with bond strength of the humidity-exposed specimens and showed the same Arrhenius dependence, suggesting that moisture absorption by the adhesive was the limiting factor in bond performance and that EIS has the potential to nondestructively track bond health and warn of deterioration.

Detection of Moisture in Adhesive Bonds Using Electrochemical Impedance and Dielectric Spectroscopies

“…There was no practical means of measuring the ingress of moisture into the bondline prior to bond failure. Recently, moisture absorption has been tracked by measuring changes in the dielectric constant of the adhesive by electrochemical impedance spectroscopy (EIS) [14][15][16][17][18][19][20][21][22][23] and dielectric spectroscopy [24][25][26][27][28][29][30][31][32][33][34][35][36][37].…”

“…Davis and co-workers have adapted an EIS-based coating health sensor technology to detect the initial degradation of a bondline resulting from the ingress of moisture and to correlate the sensor measurements with mechanical properties [15][16][17][18][19][20][21][22][23]. This approach eliminates the immersion requirement and allows these measurements to be obtained under ambient conditions of an adhesive sandwiched between two adherends.…”

Change in Electrochemical Impedance Spectrum of Al/CFRP Adhesive Lap Joint by High Temperature, High Humidity-Cold Cycle Test

“…Resins generally age owing to water absorption from the environment 2) that results in deterioration of the mechanical properties 3) and a decrease in impedance 4,5) (deterioration of anticorrosion effect on metals). In addition, the impedance of epoxy resins immersed in saltwater changes with temperature.…”

Fractional-order modelling of epoxy resin

“…The alternative non-destructive testing has been also studied, namely those techniques based on ultrasound [4], acoustic emission [5], holographic interferometry [6], thermography [7], radiography [8], Lamb waves [9] and electrical impedance spectroscopy (EIS). EIS has been adopted for monitoring the curing process of structural adhesives [10], the debonding process [11], the bond-line degradation [12], the adhesive contamination [13], integrity monitoring [14] and others [15,16].…”