Stiffness of plate arrayed with holes? 1

[JMOwen]

I'm trying to determine the stiffness of a perforated plate 25mm thick arrayed with through holes 1.7mm dia on a 4.5mm horizontal and vertical pitch. The holes are in a square array (not honeycombed.

I've found data on perforated sheet but not thick plate.

Anyone out there had a similar problem?

Justin

 

[GregLocock]

First thought:

Just discount E (or G) by the lost volume of steel. So if you drill out 30% of the metal, drop E by 30%

Second thought: that is not a conservative solution, your square array makes things worse by defining hinge lines. Analsyse each hinge, and the intervening strip.

Sorry, that's as far as I got!

Cheers

Greg Locock

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

 

[prex]

ASME VIII defines an equivalent Young's modulus and Poisson's ratio for perforated thick plates subject to bending (the tubesheets of heat exchangers).
For your geometry, the ligament efficiency of the square pattern is [η]=(p-d)/p=0.622, and
E[sup]*[/sup]/E=0.74
[ν][sup]*[/sup]=0.29
These are graphically determined on a chart, unfortunately there is no interpolating formula.
Note that the elastic modulus is somewhat smaller than what was suggested by GregLocock: his method is in fact correctly applicable to (bending) stresses, more than to stiffness.
Here TEMA may help: they define an efficiency to bending stresses as [η]=1-0.785d[sup]2[/sup]/p[sup]2[/sup] that is exactly the solid to unperforated area ratio (the formula is for a square pattern, but for a triangular pattern another formula gives again the area ratio).

prex

http://www.xcalcs.com

Online tools for structural design

 

[GregLocock]

You are right I did assume bending. That TEMA formula looks non-conservative, JMOwen's mark/space ratio is quite extreme.



Cheers

Greg Locock

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

 

[dvd]

http://www.iperf.org

Download the designer's handbook there is information on what you want.