Research Vibrothermography movie: MJPEG (13 MB) | Ogg Theora (12.5 MB)Explanation
The focus of our research is vibrothermography. This is a Nondestructive Evaluation (NDE)
technique for finding cracks, delaminations, or other flaws. In vibrothermography,
high-amplitude sonic or ultrasonic vibration causes frictional heating at cracks or other
delaminations, and the heating is measured with an infrared camera.
Major applications of this technology include maintenance inspection and manufacturing
quality assurance of jet turbine blades and discs, as an alternative to
Fluorescent Penetrant Inspection (FPI). Vibrothermography has also been used
for inspection of automobile engine parts and composites.
Vibrothermography originated with the work of Henneke et al.[1,2]. and has more recently
been improved and popularized by Favro et al.[3]. It has transitioned from a laboratory
curiosity to one of the most exciting new NDE methods. Nevertheless, substantial questions
remain about its reliability and the underlying physics of the heat-generation
process.
Most vibrothermography laboratories use an ultrasonic welder (designed for welding plastic)
as a vibration source. These welders generate 1-3 kW of acoustic power and transmit that
power through a very small tip into the specimen under test. The high energy flux creates
the risk of damage to the specimen. Moreover, the acoustic
impedance mismatch between tip and specimen often causes the tip to break contact during
each acoustic cycle creating a hammering effect. This hammering effect is extremely sensitive
and often not reproducible ("chaos"), leading to questions about reliability.
The goal of our research program is to improve the reliability of vibrothermography.
We have developed next-generation experimental apparatus, and we will use this
both to investigate the underlying physics of the heat generation phenomenon and
to apply that knowledge to verifying and quantifying the reliability of the measurement.
A key advantage of our vibrothermography system is that it uses a (relatively)
low power broadband excitation system instead of the high power single frequency
excitation used elsewhere. Broadband excitation, such as a frequency sweep (chirp),
can excite the natural resonances of a specimen and therefore can cause
enough motion to generate detectable amounts of heat at cracks with
comparatively low. In addition, the broadband excitation can be tuned to match
the specific resonant frequencies of the specimen, thereby improving the
chances of detecting a crack.
For more information contact Dr. Holland or read
the 2006 QNDE Proceedings paper References E. G. Henneke II, K. L. Reifsnider, and W. W. Stinchcomb, Thermography – An NDI
Method for Damage Detection, J. Metals 31(9) 11–15 (1979) K. L. Reifsnider, E. G. Henneke, W. W. Stinchcomb, “The Mechanics of Vibrothermography”,
in Mechanics of Nondestructive Testing, ed. W. W. Stinchcomb (Plenum Press,
New York) 249–276 (1980) L. D. Favro, X. Han, Z. Ouyang, G. Sun, H. Sui, and R. L. Thomas, Infrared imaging of
defects heated by a sonic pulse, Rev. of Sci. Inst. 71(6) 2418–2421 (2000) Selected Publications S. D. Holland, C. Uhl, Z. Ouyang, T. Bantel, M. Li, W. Q. Meeker, J. Lively, L. Brasche, and D. Eisenmann, Quantifying the Vibrothermographic Effect, NDT&E Intl. (2011).S. D. Holland and J. Renshaw, Physics-based image enhancement for infrared
thermography, NDT& E International 43(5), 440-445 (2010).J. Renshaw, S. D. Holland, and R. B. Thompson, Measurement of crack opening stresses and crack closure stress
profiles from heat generation in vibrating cracks, Applied Physics Letters 93, 081914 (2008) J. Renshaw and S. D. Holland,Full-field vibration measurement for vibrothermography Review of Quantitative Nondestructive Evaluation 27 498--503 (2008).S. D. Holland, C. Uhl, and J. Renshaw, Toward a viable strategy for estimating
vibrothermographic probability of detection Review of Quantitative Nondestructive Evaluation 27 491--497 (2008). S. D. Holland, J, Renshaw, and R. Roberts Measurement of dynamic full-field internal stresses through
surface laser Doppler vibrometry, Applied Physics Letters 91, 134101 (2007) S. D. Holland, First measurements from a new broadband vibrothermography measurement system, Review of Quantitative Nondestructive Evaluation 26 (2007) 478-483