Abstract
Bonding qualities of aluminium-alloy adhesive joints are evaluated by ultrasonic spectroscopy using the transmission characteristics for a normal incidence wave. Double-through transmission measurement was carried out for perfect bond (PB) and weak bond (WB) specimens immersed in a water tank. For the WB specimen, contamination was intentionally introduced at an adhesive-adherend interface in the bonding process. The doubly transmission coefficient was obtained by spectral analysis for the measured waveform of each specimen, showing local maxima at different frequencies. To further examine the peak behavior, the transmission coefficient was calculated by the theoretical analysis based on the one-dimensional model of a tri-layer structure in fluid. Two adhesive interfaces were modeled by linear spring-type interfaces, which are characterized by interfacial stiffnesses. The theoretical result shows that the transmission coefficient has multiple local maxima at different frequencies due to the multiple reflections at the interfaces. The frequencies of several peaks decrease when the interfacial stiffness of an adhesive interface is decreased. The interfacial stiffness is estimated for each specimen by comparing the peak frequencies of the measured and theoretical transmission coefficients. As a result, the interfacial stiffness for the WB interface is estimated to be approximately 20 percent of the PB interfacial stiffness. The peak frequencies of the measured transmission coefficients are well reproduced by the theoretical results based on the estimated interfacial stiffnesses.
