Bolt with built-in tensile strain gauge - photo and patent

[TSiArt]

[Jon]

21-second video:

[neilbourjaily]

Good chemistry/metallurgy. The same concept could be used on helmets. Plastics can be formulated so an impact would cause them to stink or to change color. That could be an effective way to detect high impact collisions involving the head.

[12bolts]

Would have liked to see what colour indication would be seen during over torqueing

[Jon]

Don't want to get lost in semantics here, but I should point out technically that I believe these bolts measure preload as opposed to torque. And I guess the advantage here (and the justification for $20 bolts) is the ability to roughly measure that preload, and NOT just the torque used to attain the preload? Someone more knowledgeable than me can expand on this.

[Ralphxyz]

Is that a left handed thread on the bolt or does blank mean it is underload and red it is free?

Ralph

[KustomsbyKent]

From what I've gleaned from our structural engineers and my own experience and research, Jon is correct in that this is measuring pre-load of the bolt so that the amount of torque to get it to that point is not relevant. The problem with using Torque to set pre-load is that quality of the threads, lubrication all help or hurt the amount of torque.
For example, a lubricated bolt can exceed the designed pre-load amount well before the recommended torque is reached. Additionally, a dry or bungered thread can cause it to prematurely hit the recommended torque without actually getting any proper pre-load.
Critical applications are engine crank bearing journals, connecting rod journals, head bolts, wheel lug nuts and many more.
Many manufacturers have gone to a torque to angle system, where you tighten it to a pre-determined lower torque, and then use a specified additional angle to get to the approximate designed pre-load.

So for some of these applications, these types of bolts would be well worth the cost for reliability and performance.