Nonlinear NonDestructive Testing
Watch a presentation of NNDT (Held for Nikolaj Sadtjikov, Russian ambassador in Sweden)
This research is supported by a grant from Vetenskapsrådet for “Nonlinear nondestructive evaluation of material conditions – resonance and pulse techniques” within which graduate student Kristian Haller is working since the summer of 2002 having so far worked with e.g. different metals, plastic-carbon fiber composites and plexiglass.
Background on nonlinear ultrasound techniques
There exist a new class of innovative nonlinear ultrasound non-destructive techniques that provide extreme sensitivity in detecting and imaging incipient damage in the form of micro-cracks or delaminations, weakening of adhesive bonds, thermal and chemical damage, etc. The sensitivity and applicability of nonlinear methods to damage is far better than what can be obtained by currently used technologies [Johnson].<7p />
There are several alternative and connected ways of nonlinear interrogation: by investigating the generation of harmonics and intermodulation of frequency components, the amplitude dependent shift in resonance frequencies, the nonlinear contribution to attenuation properties or the non-permanent (but slowly recovering) change in material parameters called Slow Dynamics [Guyer]. The concept of these methods is that the damage will be measured directly with the instantaneous detection of increase in nonlinearity. The direct connection between nonlinearity and microdamage in metals and composites is established without doubt in several preliminary conducted experimental case-studies (see Fig. 2,3).
Figure 2. Aircraft composites:left damaged, and right undamaged. Sidebands around high frequency on the left is evidence of damage (from A. Sutin)
Figure 3. Frequency sidecomponents of damaged compositeship hull.
Another advantage is that the testing may be done at relatively low frequencies so that attenuation or diffraction are not as much of a problem as for linear ultrasound.
Recent work performed at our department within the nonlinear methods include for example [Larsson], [Gunnarsson], [Rudenko] and [Hedberg 2002, 2003].
The group has very close cooperation with among others Dr. Paul Johnson, Los Alamos National Laboratory, USA (see [Guyer ; Johnson]) and Dr. Alexander Sutin, Stevens Inst. Tech.USA. Both visited the department August, 2000 and Sutin visited for one week in September 2002.
- Gunnarsson, R. Non-linear ultrasound investigation of extended plates, Master’s degree thesis, Blekinge Institute of Technology (2003)
- Guyer, R.A., Johnson, P.A. Non-linear mesoscopic elasticity: Evidence for a new class of materials, Physics Today April 1999, 30-36 (1999)
- Hedberg, C.M. ”Dynamic modelling of some nonlinear materials”, in Proceedings of Forum Acusticum, Sevilla, September 16-20, 2002. (Invited).
- Hedberg, C.M., Arnoldsson, S. and Gunnarsson, R. Two utilizations of open resonator concept in nondestructive testing, 10th ICSV Stockholm, July 7-11, 2003.
- Johnson P. , The new wave in acoustic testing, Materials World September 1999, 544-546
- Kazakov V.V., A. Sutin, P.A. Johnson, Sensitive imaging of an elastic nonlinear wave-scattering source in a solid, App. Phys. Lett. 81(4), 646-648 (2002).
-Larsson K, Silverbris A, (2003), Crack detection using non-linear wave modulation spectroscopy, Master’s degree thesis, Blekinge Institute of Technology.
-Rudenko, O.V. and Hedberg, C.M., Nonlinear response of a layer to pulse interaction in diagnostics of small inhomogenities, Doclady, Section Mechanics (Reports of the Russian Academy of Sciences) Vol. 374, No. 2, pp. 194-197 (2000)
-Theory of Nonlinear Acoustics in Fluids, (Kluwer Academic Publishers, Dordrecht, The Netherlands) by B.O. Enflo and C.M. Hedberg, 2002 ISBN 1-4020-0572-5.