Torque and Shear stress this time

In summary, the conversation discusses a question about determining the external diameter of a tube to transmit a torque of 30KNm while staying within a sheer stress limit of 80 MPa. Various formulas are provided and the final solution is given as D = 0.126781154m. The conversation also includes a thank you for the helpful comments.
  • #1
chrisking2021
7
0
I'm :confused: I'm OK at electrical theory but mechanical just doesn't compute.

I have the following question if anyone can help.

Determine the external diameter of a tube needed to transmit a torque of 30KNm if it has an external diameter twice that of its internal diameter. The sheer stress is not to exceed 80 MPa.


Any help would again be gratefully received.

Also could anyone tell me how to put formula into this thread as i don't really know how.:smile:
 
Last edited:
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  • #2
Useful formula

J = (pi/32)*(D^4-d^4)

T/J = Sheer Stress/r

T = Torque
r = Radius of external diameter
D = External diameter
d = Internal diameter

These are some formula I've tried working through but i need J or D to work it through.
 
  • #3
You have everything you need. J is a function of D only. D and D/2.
 
  • #4
Chrisking2021,
As Cyrus mentioned. All the info was given.
To finish off the question, for those like me found the thread.
The formula should look like:

T=τ/r*(J)
D= external diameter in meters

30*10^3 [Nm] = 80*10^6 [Pa=N/m^2] / (D/2) * (pi/32)*(D^4-(D/2)^4)

When solved
D=.126781154m

Thank you for the comments. I used this thread to help study for the FE exam.
 

1. What is torque?

Torque is a measure of the twisting force applied to an object. It is calculated by multiplying the force applied by the distance from the axis of rotation to the point where the force is applied.

2. How is torque different from shear stress?

While both torque and shear stress involve forces applied to an object, they act in different directions. Torque causes rotational motion, while shear stress causes deformation or sliding along a surface.

3. What factors affect the magnitude of torque and shear stress?

The magnitude of torque is affected by the force applied and the distance from the axis of rotation. Shear stress is affected by the force applied and the area over which the force is distributed.

4. How can torque and shear stress be calculated?

Torque can be calculated by multiplying the force applied by the distance from the axis of rotation. Shear stress can be calculated by dividing the force applied by the cross-sectional area of the object.

5. What are some practical applications of torque and shear stress?

Torque is important in many mechanical systems, such as engines and motors, where it is used to generate rotational motion. Shear stress is important in structures and materials, as it can cause failure or deformation under certain conditions.

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