how to calculate bolt tightening torque

How to calculate bolt tightening torque.
By applying tightening torque, we are basically stretching the bolt. which in turns creates a tensile stress in the bolt.
The tensile load developed in the bolt due to tightening torque is known as preload. The tensile load in the bolt, creates a compressive force in the bolted joint. which is often known as clamping force.
When we apply tightening torque to a bolt, it seems that all applied torque converts into preload. But unfortunately only 10% of the applied torque convert into useful preload.
And about 50% of the applied torque is used to counter, frictional resistance between the nut and the washer or nut and joint.
And remaining 40% of the applied torque is used to counter frictional restraint between threads of nut and bolt.
The tightening torque also depends on the nut factor K.
The value of nut factor depends on Fastener Materials, type of Coatings and lubricant.
if we load the bolt up to its yield point. Than bolt will have permanent deformation and it cannot be used again. So in case of fasteners we define a term proof strength or proof load.
Proof strength can be defined as the maximum tensile stress that can be applied to a bolt, which will not result in plastic deformation. In other words, the material must remain in its elastic region when loaded up to its proof strength. Proof strength is typically between 85 to 95% of the yield strength.
In case of non-permanent bolted joint, where we want to reuse bolts. In such applications bolt should be loaded up to 75% of its proof strength, this is to avoid permanent deformation in bolt.
So for non-permanent bolted joint preload can be calculated as 0.75 times proof strength multiplied by bolt stress area.
And if the bolted joint is permanent, then we can load the bolt up to 90% of its proof strength. Therefore, in case of permanent bolted joint preload can be calculated as 0.90 times proof strength multiplied by bolt stress area.
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[TushhsuT]

Nice. Short, informative and clear. Thank you!

[rohitnarayan]

Pls do an example calculation also, to verify wether viewer will be doing correctly or not.
Presentation is really very good 👍

[muhammadmudassarjaveed]

How many no of thread need to be outside after bolt, after full tightening? Which stander deal with it

[technoworks.]

Download spredsheed for tightening torque click following link.

[najibahmadi]

Thansk for a very good and detailed explanation. I appreciate if you could share where you get the tables.

[hemantpandey]

The presentation is quite amazing. If possible.. please focus on improving voice quality. Waiting for your next video ! : )👍👍👍

[zakher]

thanks a lot Dear good explanation May i know in which code you use as reference for table

[thiagob.]

Very good explanation. Greetings from Brazil...

[be_good_citizen]

Thanks for such a wonderful video.. presentation and animation is really nice.

[AnimeBakugo]

Can you please share the nut fator pdf and the spreessheet ?

[bgajul]

good presentation....what the difference between non permanent bolted joints vs permanent bolted joints ? thx..

[sooriya-ppuz]

good explanation bravo.May i know in which code you use as reference .

[jrohit]

This is an excellent explanation. Could you add links in the description to the tables used in the video?

[NikunjShah]

Please make more videos like this which can be useful for mechanical engineers

[huzaifabavar]

Can you please tell me that if screw connection loaded by 22kN force and coefficient of friction for dry Surface is 0.16
Then which screw size is suitable like M10 or M12 ???

[josephnkhata]

How do you calculate the required torque when you are tightening a material like rubber? Like a flat rubber seal being tightened with bolts against a metal surface

[SupriyoNaskar-eokc]

Why 0.938 is deducting from Pitch during stress area calculation of bolt? Please explain.

[ravikumarkanagaraj]

Hi, thanks for great video, explanations are very clear. Could you please tell from where u took the reference for pre load calculation. 0.75% of proof strength for non permanent joint is there any iso standard?? Currently i am checking for A4 70 grade bolt, there proof strength is mentioned as stress at 0.2 permanent strain is it correct? References for the formulas would be really helpful.
Thanks

[rupeshpatel]

Sir please calculate 20mm Dia Bolt ( F ) Value. Pitch 2.5m / Gr. 8.8
If possible please calculate Minimum / maximum torque in Nm.
M20 Bolt. / Gr. 8.8 / Pitch 2.5m / K= 0.15 / 600 Mpa.
We use this bolt in Railway Bridges. This is a High strength friction grip Bolt.

[brenk]

dividing by 1000 is to convert mm to meters, this step is not needed if you keep your input values the same as the output values i.e. Newtons and meters, otherwise very good