Toque vs Shear Stress
Toque vs Shear Stress
(OP)
I have an application where I am attaching a hex nut to a motor shaft with Loctite. The motor is rated to 2.3 IN-LBS and the loctite has a compressive shear strength of 3,495 PSI.
The equation for shafts, Shear Stress Max = (Torque x Radius of Shaft)/(Polar moment of inertia) only takes into account the cross-section. Does anybody know of an equation that will take into account the length of engagement as well?
Thank You
The equation for shafts, Shear Stress Max = (Torque x Radius of Shaft)/(Polar moment of inertia) only takes into account the cross-section. Does anybody know of an equation that will take into account the length of engagement as well?
Thank You





RE: Toque vs Shear Stress
T/(2pir^2l) where
pi=3.1416...
T=design torque
r=pitch radius of nut
l= width of nut
I would use 5 times the rated torque for motor startup and another 2 times for safety considerations or 10 times the rated. In any event, 3495 psi should be ok in your case.
RE: Toque vs Shear Stress
actuately this would be pi*d*(w*n) ...
d is diameter of the nut (say mean thread diameter)
w is the width of a thread
n is the number of threads engaged
conservatively, and simply, use pi*d*l ...
d is the diameter of the nut
l is the length of engagement
RE: Toque vs Shear Stress
Also, does it make any difference that it's a dynamic loading? All sorts of stuff will come lose when being vibrated that wouldn't in a static loading situation.
RE: Toque vs Shear Stress
Joe
RE: Toque vs Shear Stress
d = diameter of hole
l = length of engagement
RE: Toque vs Shear Stress
I would treat your application similar to torsion on a box/pin system. Apply a moment to the pin and get an axial load, this would directly lead to stress once you compute the pin shear area.
Note that the shear area of the box (nut) is always greater than the pin (screw). You need only worry of pin failure since the nut can take much more load.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada