smart bolts

[coppercone2]

I saw a video and I thought it was fake but it looks real. I saw the bolts before with the plastic that is supposed to get squeezed out as a tightness indicator and I thought that was pretty far out, but this takes the cake.

https://smartbolts.com/



Reminds me of a humidity tag



pricing is high, but at least its available
https://www.mcmaster.com/products/smart-bolts/

[CatalinaWOW]

At several points in my career it was demonstrated that torque is an inadequate control parameter when you are working a bolted joint at the very edges of feasibility.  All bolted joints should be designed so they don't become unloaded under the devices operating conditions.  In aerospace and some other applications you get boxed in by space and weight requirements until you must operate  the bolt fairly near its limiting tensile strength.  And this is where you find that unit to unit variations in thread form and fit, residual contamination and intentional lubrication plus other voodoo factors can make huge differences in the tension applied at a given torque.

Those strain indicating screws (there are actually multiple variants, some have built in load cells for example) can save the day in those corner applications.

[coppercone2]

I knew of those ones with electronic connections but the fact that they put a mechanical device in there is very bizarre

[CatalinaWOW]

The mechanism on these is extremely simple.  A rod up the center of the bolt with a red tip.  Unstressed the red tip touches the face of the window.  The open space around the rod is filled with colored ink.  As the bolt stretches under load the ink flows into the gap.  The density of the ink is chosen to fully obscure the end of the rod at full tension.

[Whales]

Interesting that they choose full saturation as the "correct" tightness.  I would have thought that detecting over over-torque would be good too.  Perhaps this suggests the indicators are very inconsistent?  They could put the colour scale on the bolt head too.

[Gyro]

The mechanism on these is extremely simple.  A rod up the center of the bolt with a red tip.  Unstressed the red tip touches the face of the window.  The open space around the rod is filled with colored ink.  As the bolt stretches under load the ink flows into the gap.  The density of the ink is chosen to fully obscure the end of the rod at full tension.

It's a shame the drilled out core for the indicator takes out metal that would otherwise contribute to the tensile strength. This probably means a larger diameter bolt for a given application. A nice idea but seems a diminishing return in terms of corner applications.

[Doctorandus_P]

It's a shame the drilled out core for the indicator takes out metal that would otherwise contribute to the tensile strength. This probably means a larger diameter bolt for a given application. A nice idea but seems a diminishing return in terms of corner applications.

No, probably not true. Normally the shaft of a bolt is much weaker then the head of the bolt, so when carefully designed this can be integrated into the bolt head without any strength loss.
Also, when weight is important, such as in airplanes, often bolts with a much smaller (and thus lighter) head are used.

[BrokenYugo]

Nothing beats direct stretch measurement AFAIK, so these should work quite well. They've been around a while, I think I first saw them in a McMaster catalog about 15 years ago, and that catalog was probably a few editions out of date.

No, probably not true. Normally the shaft of a bolt is much weaker then the head of the bolt, so when carefully designed this can be integrated into the bolt head without any strength loss.
Also, when weight is important, such as in airplanes, often bolts with a much smaller (and thus lighter) head are used.

While true you have to be careful to leave enough strength in the head. I'm reminded of a Mercedes AMG engine known for popping heads off the head bolts because the torx drive pocket took too much material out.

[Gyro]

It's a shame the drilled out core for the indicator takes out metal that would otherwise contribute to the tensile strength. This probably means a larger diameter bolt for a given application. A nice idea but seems a diminishing return in terms of corner applications.

No, probably not true. Normally the shaft of a bolt is much weaker then the head of the bolt, so when carefully designed this can be integrated into the bolt head without any strength loss.
Also, when weight is important, such as in airplanes, often bolts with a much smaller (and thus lighter) head are used.

According to CatalinaWOW's description, the hole goes down nearly to the end of the shaft doesn't it? ...

The mechanism on these is extremely simple.  A rod up the center of the bolt with a red tip.  Unstressed the red tip touches the face of the window.  The open space around the rod is filled with colored ink.  As the bolt stretches under load the ink flows into the gap.  The density of the ink is chosen to fully obscure the end of the rod at full tension.

That must weaken the shaft.

[coppercone2]

the point is that you might still be able to get a close sheer strength for the bolt head.

It would be weaker by the top area of the cylinder.

I assume when you harden it strain might not be equal through the bolt

What is interesting is if you drill out a bolt and harden the surface of the inner bore?

[CatalinaWOW]

With some imagination you can see that the rod doesn't have to be the diameter of the indicator dot.  Thus the loss in cross sectional area is small.  Similarly the load path from the head to the shaft of the bolt can be made almost unaffected by the indicator.

Even so, there is some small impact.  The most difficult applications use exotic steels with very tightly controlled heat treatment.  They make grade 8 bolts look like silly putty.  And are still barely strong enough so these indicator bolts are not suitable.

[Doctorandus_P]

That must weaken the shaft.

Again?
If you really want to know, then stop making such assumptions. It just make you look silly. Instead, look up some datasheets and compare different classes of bolts with their load capability. I do not find this topic very interesting, first because I'm sure they know their stuff and have done it in such a way it does not weaken the bolt. Second, I assume these bolts cost more then I'm willing to pay for them. I'm quite happy with 8.8, sometimes 12.9 if I can obtain them easily enough, but that is about my limit.

[Gyro]

@Doctorandus_P: Don't get your panties in a bunch. If you "do not find this topic very interesting" then you know what to do. If I look silly to you then so be it.

Surely we can agree that removing any cross sectional area from a solid cylinder will affect its tensile strength. Such change is easily calculable from the degree of reduction of csa and the material's properties and treatment.From their website, it does indeed have a narrower pin than the indicator head As CatalinaWOW says. I'm sure the manufactures do have a good handle on this.

I have zero intention of using them either, but certain aspects of their design and manufacture still intrigue me. Things like how the bottom of the center rod is attached, presumably by something like capacitor welding (or is it held down by a belleville spring in the head?). Looking at the 'How it works' section on the website the pin only extends down a small proportion of the bolt shaft, presumably this is sufficient to assess the full length, although it won't specifically detect anomalies issues occurring nearer the end due to mating thread anomalies. Also the details of calibrating each bolt in mass production, presumably the pin attachment has some variability even if the pins start at a precise length. It implies some elongation testing when mounting the windows. The inability to indicate that a bolt is over torqued, or is stretching in use rather than loosening (I think I would prefer something where the correct stretch is indicated by dark red rather than black). It's perfectly fine to be curious about such things without any intention of using them.

[Kleinstein]

Quite some bolt have first a part with no thread. The sensor part may not have to extend beyound that part, that is a bit larger cross section to start with.

For some applications they specify not just the torque, but a torque curve, like tighten to a specific torque and than so another 180 degree or so to that reach another torque value.

The color indictor is nice, as it may also detect of the stress is reduced later, though not detecting extra stretch. The initial elecstic part could be tested, but excessive strain is hard to test in production.

[themadhippy]

Quite some bolt have first a part with no thread

All bolts have  a part with no thread,if its threaded  along the entire length its a set screw

[CatalinaWOW]

I must point out that I am not a mechanical engineer, just did products that involved high strength bolted joints and absorbed a bunch while getting product out the door.  Also, the mechanism I described may not apply to this specific brand.  It was how something we looked into a couple of decades ago.

If you look at basic engineering texts they will show that tension in a bolt is proportional to torque.  Our team ran tests and found that this is approximately true, but that the standard deviation of observed results was close to half the mean.  When trying to use 70% or more of the ultimate strength of the best bolts available this wasn't acceptable.  Instrumented bolts were investigated but not feasible.  We ended up tracking down the sources of the variability we saw and were able to control it adequately.

The single lesson I learned from a career in that industry is that there is no method of joining things that doesn't have traps.  Bolting, riveting, welding, adhesive bonding it doesn't matter.

It also gave me great respect for those who have achieved success in challenging applications.  Like dental crowns and reflective markers on highways.

[ealex]

AVE took one apart several years ago:

https://youtu.be/ClPwlpa86bY?feature=shared

[thm_w]

Quite some bolt have first a part with no thread

All bolts have  a part with no thread,if its threaded  along the entire length its a set screw

Are you joking or serious? Clearly they were talking about partial vs fully threaded bolts.
https://www.fastenright.com/blog/the-difference-between-full-thread-bolt-and-partial-thread-bolt-uses

You can't sense in the bolt head itself because there is no stretch there.

edit: these were linked in youtube comments and look to be similar https://www.wermac.org/bolts/rotabolt.html as Kleinstein said they seem to end where the threading begins.

[themadhippy]

Are you joking or serious? Clearly they were talking about partial vs fully threaded bolts.

Maybe a language thing,but at least over here the correct  term for fully threaded bolt is a set screw

[thm_w]

Are you joking or serious? Clearly they were talking about partial vs fully threaded bolts.

Maybe a language thing,but at least over here the correct  term for fully threaded bolt is a set screw

ok, this is what is used in NA:

[Stray Electron]

Nothing beats direct stretch measurement AFAIK, so these should work quite well. They've been around a while, I think I first saw them in a McMaster catalog about 15 years ago, and that catalog was probably a few editions out of date.

No, probably not true. Normally the shaft of a bolt is much weaker then the head of the bolt, so when carefully designed this can be integrated into the bolt head without any strength loss.
Also, when weight is important, such as in airplanes, often bolts with a much smaller (and thus lighter) head are used.

While true you have to be careful to leave enough strength in the head. I'm reminded of a Mercedes AMG engine known for popping heads off the head bolts because the torx drive pocket took too much material out.

   Which engine(s)?  And was it an engine used exclusively for the AMG cars or did the non-AMG Mercedes use the same engine(s)?

    Several of the Mercedes do have a bad reputation for breaking head bolts but it was almost always because they used a Yield To Torque bolts and people re-used them when they were supposed to be replaced every time that were removed.