Dry-coupled low-frequency ultrasonic wheel probes: application to adhesive bond inspection

One of the factors limiting the more widespread use of adhesive bonding by industry is the lack of fast and reliable non-destructive testing methods. This paper describes a novel low frequency (< 500 kHz) dry coupled wheel probe which can be used to assess the integrity of three layered adhesive joints. A key novel element of this wheel probe is its operation in pulse-echo mode at low frequencies with a wide bandwidth. The system measures the first through thickness resonance of the joint which is then used to infer bondline thickness. The system is demonstrated on a range of adhesively bonded specimens of automotive specification. Also its sensitivity to alignment and coupling are discussed as are other factors limiting its operation. (C) 2002 Elsevier Science Ltd. All rights reserved.