Glue Line Nondestructive Assessment in Timber Laminates with an Air-Coupled Ultrasonic Technique

Author

Sergio J. SanabriaEmail author

Christian Müller

Jürg Neuenschwander

Peter Niemz

Urs Sennhauser

1. 1.
2. 2.

Chapter

First Online: 

20 October 2010

Abstract

Glued solid wood products have gained much importance during the last years, as they allow an efficient and versatile use of the renewable timber material. Current standardized methods for bonding quality assessment consist of tests of small specimens cut from the structure during production or visual in-service inspection. Ultrasonic diagnostics are traditionally based on discrete point measurements using contact techniques. Transducers are generally pressed onto the timber surface with a coupling gel, liquid, or membrane couplant. Large glue line defects in glued timber constructions have been detected with this method (Dill-Langer et al. 2005). The disadvantages are a low precision in signal level measurements, which are highly dependent on the coupling pressure, and that the coupling agent may deteriorate the object. Better repeatability and one-dimensional continuous scanning is achieved with roller transducers, which have been applied to defect inspection in hardwood lumber (Kabir et al. 2002). Non-linear effects have been used to assess delaminations between veneer lamina and particle board (Solodov et al. 2004); a welding piezoelectric stack couples high power ultrasound into the sample and its surface is scanned with a laser vibrometer.

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