If a nondestructive testing technique for assuring bond strength can be developed, evaluated and approved, then the use of adhesive bonds in critical structures could become widespread. Both postmanufacture and in-service testing techniques are required. While normal disbonds can be detected easily using ultrasonic testing or other methods, weak bonds and zero volume disbonds have proven extremely elusive. Six ultrasonic techniques are presented in this paper: two conventional
(double through transmission and pulse/echo) and four advanced (wideband ultrasonic spectroscopy, nonlinear ultrasonics, oblique incidence ultrasound and shear wave resonance). This paper explains these techniques and reviews their application in previous work, and gives results from recent work on specimens with contaminated adhesive. Encouraging results obtained with double through transmission, pulse/echo and ultrasonic spectroscopy are discussed. The other techniques were found to be inconclusive for contaminated bond lines.
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