Torque Coefficient

[MechiShrike]

I am trying to estimate the torque that will cause the screw threads to strip out of an aluminum heat sink. I believe I have everything nailed down except for the Torque Coeffecient, K. The value can range from .09 to .35 or so, which makes a huge difference in the failure torque.

Does anybody have a good feel for what a good number would be for zinc-plated screws into A380 cast aluminum?

Thanks for any help,

Shrike

 

[CoryPad]

If the zinc plating does not have any further treatment, then I would guess around 0.3.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MechiShrike]

Thanks Cory. That helps a lot. The numbers I was getting seemed too low, but I couldn't find a good excuse to use a value higher than .22 or so.

There's just not a lot of documentation out there.

Thanks again,

Shrike

 

[MintJulep]

Test your specific application.

 

[MechiShrike]

Thanks for the tip and I plan to, but my boss wants theoretical numbers. He says we'll test later...

He's not a fan of torque tests. He's worried about variations from the driver slipping in the screw head.

Personally, I hate plugging numbers into non-imperical formulas and running with the result.

 

[CoryPad]

The driver slipping in the screw head is way down the list of variables that are likely to affect a torque-tension test. As far as documented numbers, you can get some from Handbook of Bolts and Bolted Joints published by Dekker:

http://www.dekker.com

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.