Frictional heat is generated wherever cracks or defects are located. A thermal imaging camera highlights the cracks.
Frictional heat is generated wherever cracks or defects are located. A thermal imaging camera highlights the cracks.

Diagnosis for Wood ProblemsLooking for a hairline crack in the wood furniture? Checking the quality of the joints in assembled pieces? Researchers in Germany have developed a new method capable of doing just that.

Using ultrasound thermography, research scientist at the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut, can find defects that can’t be seen by the naked eye. In doing this, they use an ultrasound agitator working at a frequency of 20 kHz (20,000 times a second). In layman’s terms, the ultrasound agitator causes the wood to vibrate. When cracks or other defects are present, the agitation causes the parts of the material to rub together and frictional heat is produced. The thermal imaging camera then registers the heat and shows the defect. With hairline cracks, researchers says, the heat also can be seen along the length of the crack. The technique works with any species and a depth of up to 20mm can be measured.

Diagnosis for Wood Problems“We can spot the imperfections in raw timber. That is crucial for rejecting defective wood before time and money have been invested in processing it,” WKI physicist Peter Meinlschmidt said in a statement.

“Our process is especially suited for finding defects in high-quality solid wooden parts and window frame squares and to detect badly glued joints. It’s a non-destructive testing method. Applying the ultrasound agitator does leave small pressure marks though – but these aren’t an issue when you’re dealing with raw timber,” added Meinlschmidt.

According to the institute, the “high-power ultrasound thermography even allows the researchers to probe beneath the surface to uncover dowels that have not been glued and defects hidden under coatings – something that today’s much less reliable testing methods, such as mechanical materials testing or electrical measuring, are simply not able to do.”

I look forward to seeing this technology in North America in the near future.

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