Originally Posted by kmacdonald
As others have said, thermal imaging just shows surface temperature. What that represents is a guessing game
That's under-stating the same as saying that sailing is just going out on the water
and putting up some cloth to let wind
push the boat.
I've worked with a lot of bonded composites and there is a HUGE difference between an inspector experienced in the use of IR scans, one making an educated guess based on training
, and people using the tool with minimal experience or training
. The first two will use the results of the scans to know where to look closer and where to not waste time.
I was working with a guy looking at a rotor blade and there was a minor color feature in the plies which caught his eye that had not registered to me. He already knew what was going on because of his training and experience so to show me he brought out a drawing of the part and a heat gun then lightly warmed the surface for a few seconds. Because the interior
features act as a heat sink, the next scans were like having x-ray vision for the cross section. It turned out that one of the plies had been doubled or tripled, concentrating stress at the edge of the steps in plies we could not see. That was the point he used ultrasound and was able to count the number of plies and where each ended. The very expensive rotor blade could have failed through a very shortened fatigue life and was scrapped.
In the field, we would try to use IR just after dawn or sunset, because the effect of rapidly changing temperature on the surface versus the internal heat sinking characteristics was very much like using the inspectors' heat gun.