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

[Jon]

Bolt with built-in tensile strain gauge.





More: US patent #5668323

Previously:

Bolt threading GIF
Turning a bolt with another bolt - GIF
D shackle nut vibrates off of bolt - video
Miniature hunting knife made from stainless steel bolt - video

[McDesign]

I dunno'. I think the cross-section is so reduced at the "cup" for the indicator that the bolt is essentially useless for a given diameter.

All the elongation will be in that area before the bolt shank starts to load.

Maybe if your trick indicator half-inch bolt was only supposed to replace a normal 5/16" bolt . . .

Forrest

[PJs]

I dunno'. I think the cross-section is so reduced at the "cup" for the indicator that the bolt is essentially useless for a given diameter.

All the elongation will be in that area before the bolt shank starts to load.

Maybe if your trick indicator half-inch bolt was only supposed to replace a normal 5/16" bolt . . .

Forrest

I kind of agree. Elongation can occur at any place in the bolt and not necessarily linearly, usually just above the threaded section or at the base of the head or nut would be starting points. With the head and upper shank compromised by counterbore and a sight window added I would question any real accuracy of readings on that scale. I would however guess these are not used on any bolt <1".

The Abstract of the Patent is full of good details about the complexity of a threaded fastener systems but a few key factors are left out imho, like Quality control (1/100, 1/1k or 1/10k and always the Monday/Friday rule), metallurgic consistency, Grading, and Thread quality. It does however point out a LOT of other patents for this type of fasteners world wide.

The only thing I would think this is good for is a rough, visual thumb to eye rule, during initial installation torquing. Personally If something is critical, Torque Standards have been around a long time and if it needs torquing for critical reason...Use a well maintained and "Calibrated" torque wrench, in proper fashion!

PJ

[McDesign]

We just had a fastener guru from a supplier (Endries) come and give a presentation on threaded fasteners at work.
His take-away was that for critical applications, frictional factors were so variable in manufacturing assembly, and such a large absorber of tightening torque as measured at the bolt head, that measuring bolt stretch is really the only way to get a precise look at fastener clamping load. Luckily, few of our applications are that critical!

[TSiArt]

A guy on youtube AvE did a video on this type of bolt and his opinion is that this a bad idea from knowing how people can be lazy. I'll try to look up the video.

[PJs]

I would have liked hearing what all he presented. I agree to measure before and after is the true test for critical application. And I can't think of too many applications either, other than NASA and deep marine apps that might be that critical, maybe high speed rail too. I dealt with a few fastener manufactures over the years but mostly distributors that would bring people in periodically. Got to know a few of the loctite guys before they were bought out and they were a wealth of knowledge and help in difficult designs and environments.

[McDesign]

Pretty much any performance engine builder will measure rod bolt stretch instead of rod bolt torque -
https://www.jegs.com/i/ARP/070/100-9942/10002/-1

[PJs]

Maybe now day builders but I only built a few (maybe 6-8) street motors and don't remember seeing them back when, but did go through a lot of Plastigage and mic'd journals and such. Good Idea though for high power/rev motors!

[McDesign]

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

[TSiArt]