An ultrasonic oblique incidence technique is proposed to help solve the problem of interfacial weakness detection between adhesive and adherend in adhesively bonded structures. The technique employs transverse waves with an angle of incidence chosen from numerically established angular characteristics of the reflection factor for different interface boundary conditions. The interface with imperfections is modelled as a bond having a rigidity of a finite value, covering a range of delamination from 'smooth' to a 'welded' or perfect bond. Experimental measurements carried out on adhesively bonded aluminium-epoxy resin specimens illustrate quite nicely the increased sensitivity of using transverse waves for interfacial weakness detection. To improve sensitivity, a signal feature in the frequency domain is also used.
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