4 ms·

That’s true, but you can have a qualified inspector mark bolts with goo with a paint line that straddles to the fastening surface. Then you can just inspect the

That’s true, but you can have a qualified inspector mark bolts with goo with a paint line that straddles to the fastening surface. Then you can just inspect the paint line for movement, which gets you most of the same functionality at significantly lower cost. Of course, that requires a trustworthy inspector, which is one application where smartbolts become useful, if you don’t have a trustworthy inspector available at install time. But many projects that have importantly torqued fasteners (bridges, buildings, rollercoasters) have certified inspectors anyway… which is why smartbolts are a niche product I think. Speaking to the trust problem - if you trust the operator of the torquing install device, you don’t need fancy torque indication at all, just mark the paint line at install. That is the most cost effective.

mc32 5y ago
Yes, that seems like a cheaper option; however, I think when you have constant stresses over time, bolts can stretch or simply parts can wear over time and a paint score or even a frozen nut won't reveal lessened tension. Though maybe in this case the issue would have become a concern way before the bolts start to indicate a problem?
- blamazon 5y ago
  Interestingly that has kind of moved upstream to a design phase consideration in modern times due to the incredible depth of understanding we have about materials. Structures can be designed such that their expected loading will not stress fasteners beyond their ‘yield strength’, which is well characterized. Fatigue complicates the analysis, but we understand that too nowadays, although that is an understanding forged by many unfortunate consequences, such as: https://en.m.wikipedia.org/wiki/Aloha_Airlines_Flight_243 https://en.m.wikipedia.org/wiki/Aloha_Airlines_Flight_243
  - mc32 5y ago
    Maybe the following has been designed out; however, I've on occasion seen the following wear pattern which compromises the initial strength of a fastener (usually due to friction over time): _ _ _______| | _| |__/ | | ______ | |_ ____/ |_| |_|
    - blamazon 5y ago
      First, I love the plain text diagram! (Edit: not fatigue) This failure should be predictable during the design phase and that fastener is either wrongly specified or should have a recommended number of cycles after which it should be inspected and replaced if found to be out of specification. Of course, many items in our built world do not receive the same level of design scrutiny as I would wish, nor the maintenance regime…
      - auxym 5y ago
        Unless I'm misunderstanding the diagram, it does not look like fatigue at all but rather yielding from shear loading. The definition of fatigue is a small crack (in fact microscopic in the beginning) that grows through the application of cyclical loading (typically about 10k cycles is the lower bound for high cycle fatigue, which does not involve macro yielding). Thus a fatigue failure would look like a fully ruptured part , usually with two distinct zones of the fracture face: one smooth zone from crack growth ( sometimes with characteristic "beach marks") and the final sudden rupture which is usually rough. https://en.m.wikipedia.org/wiki/Fatigue_(material) https://en.m.wikipedia.org/wiki/Fatigue_(material)
        blamazon 5y ago
        You are correct, I had a brain fart.
        mc32 5y ago
        What I was trying to convey, which I didn’t do well in the diagram, was you have a bolt holding two plates together or a splice, and you have wear on the bolt shank -not necessarily shearing.
lbhdc 5y ago
The paint line is the most common method I have seen. I was an inspector and for fasteners in a critical load path we would use an ultrasound machine to measure the length of the bolt (these were installed in flange like connections). We would measure them when first installed and compare measurements after that piece of equipment was used. For really critical components we would disassemble them after every use and would perform multiple tests on each piece including fasteners.
usrusr 5y ago
That line is fine if the bolt winding itself loose is your only failure scenario, but some might have others as well. What of they clamp a part that can subtly deform in certain exceptional situations? Then you could have a bolt with zero tension that is still perfectly aligned with the marker line from when it was properly torqued. What I find somewhat surprising is that they make the "ok" indication black. The cry for attention state in red seems nicely intuitive at first glance, but given the market they serve they should be far more concerned with false negatives than with false positives and I imagine that it would be very easy for dirt or bad lighting to make a red indicator remain unnoticed in an inspection. Perhaps the color choice is an inherent property of the chemistry involved?
- chipsa 5y ago
  It's not chemical. It's mechanical. It basically covers the red with a black liquid when it's good. A different color probably wouldn't cover the red as well. The bolt is basically hollow to do this.
mrjin 5y ago
Totally agree. And two cents to add. The so called smart bolt adds movable parts in side a part supposed to be inertia and at the same time might compromise the strength in comparison with ones with the same profile and body material. And when faulty, it actually more dangerous than ordinary ones: now your torque wrench and the bolt gives different readings, which one to trust?
- chipsa 5y ago
  There's no moving parts. The bolt is hollow with a pin projecting from the tip of the bolt back to the head. When put under tension, the outside of the Bolt stretches, but the inside pin doesn't. It's not as strong as a solid bolt of the same size and material. But that's something you engineer around.

mc32 5y ago

Yes, that seems like a cheaper option; however, I think when you have constant stresses over time, bolts can stretch or simply parts can wear over time and a paint score or even a frozen nut won't reveal lessened tension. Though maybe in this case the issue would have become a concern way before the bolts start to indicate a problem?

blamazon 5y ago
Interestingly that has kind of moved upstream to a design phase consideration in modern times due to the incredible depth of understanding we have about materials. Structures can be designed such that their expected loading will not stress fasteners beyond their ‘yield strength’, which is well characterized. Fatigue complicates the analysis, but we understand that too nowadays, although that is an understanding forged by many unfortunate consequences, such as: https://en.m.wikipedia.org/wiki/Aloha_Airlines_Flight_243 https://en.m.wikipedia.org/wiki/Aloha_Airlines_Flight_243
- mc32 5y ago
  Maybe the following has been designed out; however, I've on occasion seen the following wear pattern which compromises the initial strength of a fastener (usually due to friction over time): _ _ _______| | _| |__/ | | ______ | |_ ____/ |_| |_|
  - blamazon 5y ago
    First, I love the plain text diagram! (Edit: not fatigue) This failure should be predictable during the design phase and that fastener is either wrongly specified or should have a recommended number of cycles after which it should be inspected and replaced if found to be out of specification. Of course, many items in our built world do not receive the same level of design scrutiny as I would wish, nor the maintenance regime…
    - auxym 5y ago
      Unless I'm misunderstanding the diagram, it does not look like fatigue at all but rather yielding from shear loading. The definition of fatigue is a small crack (in fact microscopic in the beginning) that grows through the application of cyclical loading (typically about 10k cycles is the lower bound for high cycle fatigue, which does not involve macro yielding). Thus a fatigue failure would look like a fully ruptured part , usually with two distinct zones of the fracture face: one smooth zone from crack growth ( sometimes with characteristic "beach marks") and the final sudden rupture which is usually rough. https://en.m.wikipedia.org/wiki/Fatigue_(material) https://en.m.wikipedia.org/wiki/Fatigue_(material)
      - blamazon 5y ago
        You are correct, I had a brain fart.
      - mc32 5y ago
        What I was trying to convey, which I didn’t do well in the diagram, was you have a bolt holding two plates together or a splice, and you have wear on the bolt shank -not necessarily shearing.

lbhdc 5y ago

The paint line is the most common method I have seen. I was an inspector and for fasteners in a critical load path we would use an ultrasound machine to measure the length of the bolt (these were installed in flange like connections). We would measure them when first installed and compare measurements after that piece of equipment was used. For really critical components we would disassemble them after every use and would perform multiple tests on each piece including fasteners.

usrusr 5y ago

That line is fine if the bolt winding itself loose is your only failure scenario, but some might have others as well. What of they clamp a part that can subtly deform in certain exceptional situations? Then you could have a bolt with zero tension that is still perfectly aligned with the marker line from when it was properly torqued. What I find somewhat surprising is that they make the "ok" indication black. The cry for attention state in red seems nicely intuitive at first glance, but given the market they serve they should be far more concerned with false negatives than with false positives and I imagine that it would be very easy for dirt or bad lighting to make a red indicator remain unnoticed in an inspection. Perhaps the color choice is an inherent property of the chemistry involved?

chipsa 5y ago
It's not chemical. It's mechanical. It basically covers the red with a black liquid when it's good. A different color probably wouldn't cover the red as well. The bolt is basically hollow to do this.

mrjin 5y ago

Totally agree. And two cents to add. The so called smart bolt adds movable parts in side a part supposed to be inertia and at the same time might compromise the strength in comparison with ones with the same profile and body material. And when faulty, it actually more dangerous than ordinary ones: now your torque wrench and the bolt gives different readings, which one to trust?

chipsa 5y ago
There's no moving parts. The bolt is hollow with a pin projecting from the tip of the bolt back to the head. When put under tension, the outside of the Bolt stretches, but the inside pin doesn't. It's not as strong as a solid bolt of the same size and material. But that's something you engineer around.