affect of torque on critical buckling of shaft?

[hobbs101]

Hi. I've got a powerscrew that is applying a compressive force of 25kN. The torque applied by the actuator to the nut to move the powerscrew is 200Nm. The shaft has a slenderness ratio of 124.

I've calculated using the Euler formula that I have a good x10 safety factor on buckling, but this doesn't take into account the torque applied to the shaft.

Does torque affect the critical buckling force? If it does how do I calculate the buckling force taking torque into account?

Thanks.

Hobbs101
Mechanical Design Engineer

 

[LiftDivergence]

A compressed and twisted shaft will have a different critical buckling load than a shaft in pure compression. Maybe start by having a look at Timoshenko and Gere's treatment of this in their classic book "Theory of Elastic Stability". The result is equation 2-74 (page 157) although I recommend reading that section of the chapter to determine applicability to your scenario.

You will need to make a conservative estimate / evaluation of the pure torsional moment applied to the shaft by the actuation process. Basically the formula has an additional term accounting for the applied moment, and reduces to the Euler formula when the moment is zero.

That might be a good starting point?

Keep em' Flying
//Fight Corrosion!

 

[hobbs101]

Ah yes, that look good. Thanks.

Hobbs101
Mechanical Design Engineer

 

[desertfox]

Also try this link

http://files.engineering.com/downlo...1-417d-a469-590769ea8fc4&file=powerscrews.pdf

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[hobbs101]

Thanks desertfox, but I don't see any reference to combined compression and torsion in that document. Have I missed it?

Hobbs101
Mechanical Design Engineer

 

[desertfox]

Hi hobbs101

No I think you are correct although the combined stress is detailed in chapter 3.2.

It appears to me they treat the buckling as a separate issue and to be fair that's how I would consider it too using a large factor of safety.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[SDMAX]

Hobbs101,

Combined buckling and torque is an area that has seen significant research in the offshore industry, particularly for downhole drillpipes and other tubulars.

Some of the initial research was performed by Lubinski and recently Stefan Miska at the University of Tulsa. I would recommend you do a web search on buckling+torque+drillstrings and you should get some valuable background information.

I will also try and upload a paper with background data.

 

[SDMAX]

Attached files for reference

 

[hobbs101]

Thanks, I'll have a read through.

Hobbs101
Mechanical Design Engineer

 

[tbuelna]

The end constraint conditions of your jackscrew will have a significant effect on buckling stability. Is the jackscrew tightly constrained radially at each end over its full travel? Or is the drive nut threads the only thing constraining the jackscrew at one end? Did you consider the minor thread diameter of the jackscrew in your buckling analysis?