Maximum Torque to Break a Thread
Maximum Torque to Break a Thread
(OP)
Hi,
I have a threaded connection which has a direct tensile load to break the thread is 12,000 lbf. I am trying to find the torque that can supply this load to the thread to break it. The thread is 0.4375-20UNF.
The load on thread and the torque load is perpendicular as you are aware of. can i apply the "direct tensile load to break the thread" into the torque formula on the machinarys handbook to calculate the maximum torque to break the thread.
If you have any questions, please let me know.
Mechatron
I have a threaded connection which has a direct tensile load to break the thread is 12,000 lbf. I am trying to find the torque that can supply this load to the thread to break it. The thread is 0.4375-20UNF.
The load on thread and the torque load is perpendicular as you are aware of. can i apply the "direct tensile load to break the thread" into the torque formula on the machinarys handbook to calculate the maximum torque to break the thread.
If you have any questions, please let me know.
Mechatron





RE: Maximum Torque to Break a Thread
If it is only a threaded connection, then you need to remove the bearing friction component and keep the thread friction and thread pitch components.
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Maximum Torque to Break a Thread
Is there a formula for find the maximum torque (ie before the thread breaks) for threaded connections.
RE: Maximum Torque to Break a Thread
RE: Maximum Torque to Break a Thread
What is it you are looking for, an absolute do-not-exceed torque, or a guaranteed breaking torque? Do you need to be accurate?
Is there any chance you can do this by counting turns of the nut? This may be more predictable and nut friction and the force required to cause plastic deformation.
JHG
RE: Maximum Torque to Break a Thread
I am theoritically trying to the find the absolute, do not exceed torque. I want the thread material to go beyond its elastic limit and reach the ultimate clamping force which is in the plastic region. If you torque beyond this point the thread will elongate but the tension will drop and eventually fracture.
can you help
RE: Maximum Torque to Break a Thread
then dT = Fsu*2*pi*r^2dr and Tult = Fsu*3*pi*r^3
RE: Maximum Torque to Break a Thread
T = 2/3 · π · r3 · τ
where
T = torque
π = 3.141 592 654
r = shaft radius
τ = shaft material shear strength
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Maximum Torque to Break a Thread
You need a stress strain curve for your bolt material so that you can find the maximum stress point. Your material looks like a grade five bolt to me. A similar steel material in my machine design book elongates 19% at fracture. For a reasonably long bolt, this should be quite a few turns of your nut, allowing for accurate control of force.
The primary cause of wrenching torque is friction. This is hard to predict accurately.
JHG
RE: Maximum Torque to Break a Thread
also a good point ... is the torque applying preload (like in the real world) or is this a theoretical application (maybe torquing against a jam nut, so there wouldn't be any preload) ?
RE: Maximum Torque to Break a Thread
RE: Maximum Torque to Break a Thread
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Maximum Torque to Break a Thread
Do you need 12,000 lb preload, or are you specifically looking to achieve the "maximum"?
It looks like about 1200 lb-in would exert the 12,000 lbs you're after. If you could use a SHCS the bolt would take it easily.
htt
HoloKrome catalog page 32 (pdf page 39)
I don't think intentionally using the thread region as the limit is commonly done. Too many variables. Torque-to-yield bolts and angle tightened bolts (same thing) plastically stretch the shank, for several thousandths of an inch of initial elongation and greater tolerance for joint preload load loss due to embedment,etc.
Designing with relieved shank bolts longer than 5 or so diameters assigns the stretching function to the entire bolt shank, which can be finished nicely to avoid stress concentration.
http://www
RE: Maximum Torque to Break a Thread
The equivalent stress with many names (distortion energy/octahedral shear stress/Hencky/von Mises ) is a yield criterion based on shear. For fracture in shear, it is common to use the value 0.6 · tensile fracture stress, which is obviously close the 0.577 value. However, the non-uniform stresses due to torsion require a different analysis. The sand hill analogy has been used to find the limit torque of polygonal shafts. This, and other techniques, result in the 2/3 value. A really good article on the subject is Strain 41 (2005) 31-32.
Regards,
Cory
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Maximum Torque to Break a Thread
I will check out the Sand Hill Analogy. Thanks for the tip.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
RE: Maximum Torque to Break a Thread
http://www.hexagon.de/dose/dose-1e.pdf