I wonder why this is not used on airframes and engines?
Norbar is another company selling this stuff, and there are probably many others.
It is a bit more time consuming than a torque wrench, because you have to take one measurement with each individual bolt in the unloaded state, to get the reference length. It also doesn’t work where the bolt is not geting much of a stretch; it states that negligible elongation occurs when tensile stress levels are less than about 10% of the material’s ultimate tensile stress, and it won’t work with short bolts.
It would seem to be perfect for the crankcase through bolts which, if done incorrectly, fail with disastrous results.
In some cases the procedure is already used but with a micrometer used to measure the elongation. On our engines this is done on conrod bolts. The ultrasonic method does not need access to both ends of the bolt.
The usual way to get an accurate tension in a bolt (when that is needed), is to use a bolt tensioner. A torque wrench is not a precise method for obvious reasons, but it is good enough to prevent damaging over/under torquing, and applying roughly equal tension in all the bolts (seasoned mechanics are in fact better at it using only their hands).
A bolt is not always a “bolt” either. In aircraft structures, shear bolt, is the common bolt type.
That’s really clever too. Didn’t know this existed…
It needs good access to the bolt though.
Peter wrote:
It needs good access to the bolt though.
Not particularly IMO. Besides, it’s purely a design consideration. If precise tension is needed in the bolts, then the item must be designed so this is possible to achieve.
We can do a lot of things with electric screwdrivers nowadays, much smarter than a good old torque wrench.
You have to learn and calibrate your bolt joints though.
When I originally read about this method I thought they used the variation in the resonant frequency of the bolt to indicate its tension.
Instead, they are simply measuring its length, which is obviously harder to do accurately and impossible for short bolts, etc. Also it doesn’t work if the bolt is not getting stretched much because the stuff it is clamping together is getting squashed.
Resonant frequency variations have been used in other areas e.g. the classic mass flow measurement method. That was invented by a guy I was at univ with.
