screw torque/clamping pressure 1

[gopalka]

Hello,
The problem I am having is this:

I have a 3"x3" soft aluminum plate clamped on each corner with a screw. I need to know how to find the pressure the plate is transfering to the surface below.

If anyone has any hints on how to do this I would appreciate it.

Thanks,

 

[CoryPad]

If you know the plate thickness t, screw head outer diameter d₁, and screw pretension F, then you can calculate the pressure p per screw.

Assume the force spreads out from the screw head into the Al plate with a 30 degree angle. This means the effective diameter d₂ under the Al plate is:

d₂ = d₁ + (2t)/&[ignore]radic[/ignore];3

Then

p = F/A

where

A = (&[ignore]pi[/ignore];&[ignore]middot[/ignore];d₂²)/4

 

[drawoh]

gopalka,

How accurate do you have to be?

You have not indicated the size of the screw, or the specified torque. I have seen literature on how to predict how people will install fasteners without a specified screw torque, but boy is it approximate!

Even the standard screw torque methods are approximate.

JHG