Characterization of interfacial degradation in adhesive joints using EMAT's

An ultrasonic technique utilizing horizontally polarized shear (SH) waves was modeled and developed to characterize early stages of interfacial degradation damage in adhesive joints. Electromagnetic acoustic transducers (EMAT's) were used to implement the technique.; A finite element model for ultrasonic SH wave propagation in adhesive joint was developed. The numerical model was used to aid the design and experimental evaluation of the inspection technique. Interfacial damage effects were modeled in the wave propagation program. An approximate linear relationship between the percentage of damaged interfacial area and reflected SH wave amplitude was found.; Accelerated degradation experiments under controlled laboratory conditions were performed on adhesive joints. Prototype EMAT's capable of generating and receiving SH waves were designed, constructed and optimized to produce the maximum ultrasonic echo signals possible. The SH EMAT's and conventional piezo-electric transducers were utilized to perform ultrasonic C-scans on degraded joints.; The scan results revealed approximately twice the sensitivity of SH waves compared to that for P and SV waves to both early and late stages of the joint's interfacial degradation. However, P waves exhibited higher spatial resolution for detecting individual water patches compared to SH and SV waves. SV waves were found to be the most sensitive wave mode to surface distortions on the adhrend's surface.