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

[PJs]

Check these three slides from that presentation out - the first shows just how little of applied torque actually goes into stretching the bolt - remember, a bolt is a spring that has to be stretched to work.

Second slide shows the components of a 4-lubricant comparison

Third slide shows the huge variation between applied torque (first red-marked column) and the tension generated in the bolt (second red-marked column) - only variable was the lubricant or lack thereof.

Forrest

Thanks for sharing the slides, Forrest. After looking at these for awhile, pondering and a bit of research, I do think the last slide has some interesting values as you pointed out. Particularly the thread torque to peak tension and the results of the Zinc Flake example was surprising to me. However, we would likely assume these test were done on their fasteners (with no mention of ASTM standards used in manufacture or OA length {ratio of thread to shank length}) other than Grade 5 Hex Cap, Gr2 full nut and yellow zinc washer; Nor did it state where the single washer was located (head or nut), and more curious to me was how the friction of 9050lbs was calculated or measured, and what the numbers in the 3 columns on the left (Thread, head, ref.) mean. The K-Factors seemed appropriate to ASTM standards, and the Peak ON torque (Head) seemed appropriate to me, but must we assume all these values were to achieve a Target Clamp Load of 9791 lbs. from slide 2?

Slide 2 showing their test setup, definitely looks legit and calibrated in a lab. Chart 1 though, is a bit crayon for me as it is only a resultant pie chart from, I assume a spreadsheet, that represents a "Clamp Load-Vs_Applied Torque" but gives statistics for friction, which appear to be within the ball park based on this White Paper by Ralph S. Shoberg, P.E., Director of Technology, PCB Load & Torque, Inc. The good (pertinent) stuff starts at the bottom of page 4. His other paper "Tightening Strategies for Bolted Joints" is also of interest in the discussion where he details all the complex variables, proper test procedures and outlines methodology and math for Torque-Angle Signature Analysis as shown in your slide 3 in the 2 columns next to peak tension giving insight to those numbers in the "Final Angle (deg)" column.

Sorry but I'm kind of a stickler on test methodology, Statistic and Data. My credo is/has been, Discernment in all things. Not to say I don't Jump to Incorrect assumptions sometimes, but I try...consciously.

Although this discussion rises above the average HMT/shop it does give some insights to properly choosing and applying fasteners to what ever we design or build. It says volumes to things to think about, like; if, where, and what washers are used, clearance hole sizes, material finish, grade, thread pitch, etc. and the all important question...does it really need to hold the planet together and will it hurt someone if it fails? Thankfully engineers, manufacturers, and Standards, makes it relatively simple to choose, get and use fasteners in our projects at home or professionally for every day use and the opportunities to push the boundaries of technology because we all have added to the advancements.

Thanks Jon for lighting the candle and Forrest the discussion, hopefully our members find some good value and insight to it.

I watched AVE's Vid when he first did it but will need to watch it again for any further comment, if any. Thanks TSiArt for bringing it forward here!

PJ

[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.