How to Understand Angular Torque and Torque to yield?
wbtools.com.au
Angular & torque to yield info
- Thread starter RINGER
- Start date
wbtools.com.au
Seasink,
That's one of my pet peeves. It seems this sort of nonsense has taken hold:
uxmovement.com
Did book publishers ever get complaints about their ink being too black?
For fellow geeks, besides tweaking the CSS in the web-developer screen, I have found it useful to install "Stylish" (on Firefox) so that tweaks are remembered. AussieFrogs text is ok, but it was still good to set a style so embedded links would stand out.
That's one of my pet peeves. It seems this sort of nonsense has taken hold:
Why You Should Never Use Pure Black for Text or Backgrounds
Did you know that pure black text can cause eye strain? A survey found that “58 percent of adults in the U.S.” have experienced eye strain from working on computers. Designers can do their part to reduce the likelihood of eye strain on their designs by paying attention to the color of black they...
uxmovement.com
For fellow geeks, besides tweaking the CSS in the web-developer screen, I have found it useful to install "Stylish" (on Firefox) so that tweaks are remembered. AussieFrogs text is ok, but it was still good to set a style so embedded links would stand out.
As I am in an argumentative mood today I will comment on some of that information from WB tools.
Firstly TTY bolts are used because they more accurately get to the desired clamping force than the old way. More accurate and less variation because it relies on the basic properties of steel material which are quite reliable and tested.
Secondly the method is more easily achieved on the production line by 'robots' or machines. Instruction to do a specified angle is much easier to program into a machine sequence than a variable end point like a torque. Hmm this might be the clincher today.
Thirdly the idea that it is verbotten to ever reuse a TTY bolt is part of the myth of the world "yield". The bolts are quite capable of yielding a 'long way' before they suffer any local area reduction and get to necking and danger of failure. Most manufactures do give a length measurement under the head for safe reuse. I have reused head bolts and crankshaft pulley retaining bolts and had no failures. A good clean and detailed inspection and measurement will be required. But that does not say you should do it !
Jaahn
Firstly TTY bolts are used because they more accurately get to the desired clamping force than the old way. More accurate and less variation because it relies on the basic properties of steel material which are quite reliable and tested.
Secondly the method is more easily achieved on the production line by 'robots' or machines. Instruction to do a specified angle is much easier to program into a machine sequence than a variable end point like a torque. Hmm this might be the clincher today.
Thirdly the idea that it is verbotten to ever reuse a TTY bolt is part of the myth of the world "yield". The bolts are quite capable of yielding a 'long way' before they suffer any local area reduction and get to necking and danger of failure. Most manufactures do give a length measurement under the head for safe reuse. I have reused head bolts and crankshaft pulley retaining bolts and had no failures. A good clean and detailed inspection and measurement will be required. But that does not say you should do it !
Jaahn
Not pale enough ...
Hi.
I've learnt a new word today - verbotten.
I guess reuse depends if the bolt has been stretched into the elastic zone or past the yield point into the plastic zone. A good article from below source. It seems that the torque method is still OK for elastic zone tightening:
Angle of rotation method is a method for controlling the clamp force by control of the tightening rotation angle from the snag point of the screw head, or nut, by calculating the angle on a pointer scale (a protractor), for example, or with an electrical detector; it can be used for both elastic region and plastic region tightening.
Incidentally, the snag point is the point at which the required tightening torque acts to force the screw and seating surface tightly together.
However, the straightforward torque method is often preferred for elastic region tightening, since the axial force varies noticeably with the rotation angle.
On the other hand, in plastic region tightening, the change in the axial force due to tolerance in rotation angle is smaller. For that reason, it may be possible to control the angle by sight watching the hexagonal form of the bolt or nut.
Vol.7 Screw Tightening Control Methods | NBK | The Motion Control Components
Although fastening objects using the axial force generated from tightening is the main role of screws (bolts), in actual work, I think there are many people who control the torque by tightening with a torque wrench, because it is difficult to directly monitor the axial force, and so guarantee...
www.nbk1560.com
Also the below graph clearly illustrates both the difference in, and variability of, clamped loads for the same torque with either dry or oiled threads/heads. Often it is difficult to obtain reliable information to ascertain if torqueing is to be lubricated or dry.
The graph here illustrates the torque-to-load behaviour between a dry installation and a lubricated installation. While the preload scatter at a given torque is quite random, you can influence the variability of that scatter by this simple modification.
Effects of Lubrication When Reusing Fasteners
By lubricating the fastener before every use, not only can friction be reduced to improve torque-to-load ratio, friction scatter can also be reduced to improve preload accuracy.
www.nord-lock.com
Cheers.
Whippet, glad to introduce a new useful word 
. Some interesting stuff for me to digest too.
I have done quite a lot of load/extension tests (stress/strain diagrams) on actual tensile testing machines. I have also done testing on real bolts and fasteners in my career at different times.
What I have observed is that the diagrams as produced in books and that Google dredges up are usually not a true diagram IE on the extension axis(strain axis). They are modified to exaggerate the important theory features of the curves and over time the true diagrams now shown are not a true image of what extension really happens at the elastic/yield/initial plastic area of the graph, compared to the rest of the diagram, > plastic > peak > failure part of the graph. It increases by a factor of about x100 would you believe with metals. That is a surprise to a lot of people who think they know what the graphs look like.
Of course lots do know but to find a reference on the web is difficult now and who actually does real testing. The importance for the subject here is that the plastic range after the elastic range is quite loong-----------------------by a lot of extension. In normal strength steel for bolts, whatever grade that might be, the plastic extension might be 100 x more than the elastic extension and a dual scale was used after removal of the precision extensometer and the graph had a "change of scale" note'. So easily noticed and plenty more where that comes from, sort of comment !! Note very high strength brittle steels are not used normally in vehicles for obvious reasons.
Here is a reference I did find with some interesting and accurate diagrams IMHO. There are several interesting metals diagrams but note one shows the dual scale diagram 'for accuracy' P15 and a complete diagram on P8 with both scales. Sorry about the ksi V in/in axis scales ! Also the pastle colours used !
Jaahn
http://faculty.mercer.edu/jenkins_he/documents/StressandStrain.pdf
. Some interesting stuff for me to digest too.I have done quite a lot of load/extension tests (stress/strain diagrams) on actual tensile testing machines. I have also done testing on real bolts and fasteners in my career at different times.
What I have observed is that the diagrams as produced in books and that Google dredges up are usually not a true diagram IE on the extension axis(strain axis). They are modified to exaggerate the important theory features of the curves and over time the true diagrams now shown are not a true image of what extension really happens at the elastic/yield/initial plastic area of the graph, compared to the rest of the diagram, > plastic > peak > failure part of the graph. It increases by a factor of about x100 would you believe with metals. That is a surprise to a lot of people who think they know what the graphs look like.
Of course lots do know but to find a reference on the web is difficult now and who actually does real testing. The importance for the subject here is that the plastic range after the elastic range is quite loong-----------------------by a lot of extension. In normal strength steel for bolts, whatever grade that might be, the plastic extension might be 100 x more than the elastic extension and a dual scale was used after removal of the precision extensometer and the graph had a "change of scale" note'. So easily noticed and plenty more where that comes from, sort of comment !! Note very high strength brittle steels are not used normally in vehicles for obvious reasons.
Here is a reference I did find with some interesting and accurate diagrams IMHO. There are several interesting metals diagrams but note one shows the dual scale diagram 'for accuracy' P15 and a complete diagram on P8 with both scales. Sorry about the ksi V in/in axis scales ! Also the pastle colours used !
Jaahn
http://faculty.mercer.edu/jenkins_he/documents/StressandStrain.pdf
Hi.
Interesting to know of your prior experience. There are some clever, experienced members on this forum across a range of disciplines.
Interesting PP pages. If the speaking notes were available that would assist to understanding some of the graphical information.
How would one know if a bolt is used in the elastic range compared to the plastic range, for a particular application? Maybe torque wrench for elastic, and initial torque/angle turn for plastic?
For the average mechanic in a critical torque to yield application eg: conrod, mains, cycl head etc might it be safer to just replace the fasteners?
Cheers.
Interesting to know of your prior experience. There are some clever, experienced members on this forum across a range of disciplines.
Interesting PP pages. If the speaking notes were available that would assist to understanding some of the graphical information.
How would one know if a bolt is used in the elastic range compared to the plastic range, for a particular application? Maybe torque wrench for elastic, and initial torque/angle turn for plastic?
For the average mechanic in a critical torque to yield application eg: conrod, mains, cycl head etc might it be safer to just replace the fasteners?
Cheers.
Wippet good questions. To answer the last first then yes probably safest to spend more money and get new fastners !! Possibly made in some cheap asian or european backwater but who knows the quality of the steel and the production.
Look at the manufacturer recomendations for the method of tightening the fastners. If it is a torque setting only then it is most likely older and in the elastic range. If it has angle specs after some initial small bedding torque, then almost certainly into the plastic range. The proper specs will usually give an inspection and a max length under the head for reuse. That is to check it has not been reused before or abused.
Interestingly in the old days some British motorbike bigend bolts were tightened to a stretched length using a micrometer on the length of the bolt. This also gave a set preload independant of torque or friction but was not into the plastic range. I believe some critical aircraft bolts were normally tightened similarly to a specific measured stretch.
The idea of the angle method is the preload is calculated by the pitch of the thread and that is certain. So say two x 90deg turns is half the distance of the thread pitch stretched.
Jaahn
Quality rod bolts such as ARP2000 or 625+ are done that way. I use a rod micrometer and typically stretch a 5/16” bolt 0.0055”.
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Hi.
Thanks Peter, that ARP website has lots of interesting reading. https://arp-bolts.com/p/technical.php
Here is one sentence from the Common Failures tab: "Many connecting rod bolt failures are caused by insufficient preload."
I also was not aware of the many specialized alloys used for high performance fasteners.
Plus some interesting discussion regarding different methods of preloading and also their ARP Ultra-Torque lubricant. They state that new fasteners require 5-7 load unload cycles to "level out" the initial friction to achieve consistant torque to preload.
Cheers
A different Torque To Yield tightening method.
I remember torquing up 3.25inch dia. TTY studs on a 132inch dia. butterfly valve on a large dam. We flogged them up with a 28lb sledge hammer using the part turn method. The first couple of studs were tightened with the stud's overall stretch measured and the nut's rotation recorded.
All studs were reused on the valve's removal for maintenance.
Caution: Take care not to put dents in your bonnet if you use this method!
I remember torquing up 3.25inch dia. TTY studs on a 132inch dia. butterfly valve on a large dam. We flogged them up with a 28lb sledge hammer using the part turn method. The first couple of studs were tightened with the stud's overall stretch measured and the nut's rotation recorded.
All studs were reused on the valve's removal for maintenance.
Caution: Take care not to put dents in your bonnet if you use this method!
For those, like me, who are not familiar with the tools required for stretch measuring, here are some pics of specific rod bolt stretch gauges.
The rod bolts for this have a center in the ends to hold the gauge ballends. I note the head end has the center recessed to enable better access to the head.
Or if you need to follow advice from BIGRR the last tool may be for you !
Jaahn
The rod bolts for this have a center in the ends to hold the gauge ballends. I note the head end has the center recessed to enable better access to the head.
Or if you need to follow advice from BIGRR the last tool may be for you !
Jaahn
I do not know what that comment is for ??
We are having a conversation here and some people are interested in the subject that was originally posted and it is in the Technical and Performance section. Those of us that do wish to learn newer technologies and work practices do take the opportunity to google the subjects posted here and have a discussion. Others share their experience. Possibly better than looking at hundreds of odd cars for sale.
So Sj B if you do not like it then I suggest you please just move on without any silly comments. If you wanted to join the conversation usefully then look for some articles or references or even give your experiences, that are in your acceptable units
Unfortunately a lot of technical information is still coming from the US and they do use inches and pounds. . Actually I can and have worked in either the US or the SI system.
Jaahn
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