# Cantilever Effect? Plate Deflection Help!

1. Jun 3, 2010

### Khowe9

I'm working on some stress analysis for work. I'm designing a plate, part of which is meant to deflect under a load. Due to this sheet metal plate being somewhat non-straight forward geometry, I'm unsure if I'm attacking it correctly.

I'm putting symmetrical cuts into the plate to allow for easier deflection. Since its not one solid thickness, I didnt know if I could use a cantilever equation. I'm trying to make sure I have an adequate safety factor, but I seem to get numbers I dont trust when I do hand calculations. These numbers also dont match the FEA numbers I get (not that I trust those, either....)

I've included pictures, one of the CAD model showing what the actual plate looks like. The other, a cross section view at the cutout (hopefully this is the correct way to analyze).

Any help or suggestions would be greatly appreciated. I'd like to do well on this project!

http://img210.imageshack.us/i/beam1.png/

http://img121.imageshack.us/i/beam2.png/

I've been using the following equations:

Deflection at B = (Deflection at A)(Height of A/Height of B)

And for stress:

Stress = (3*(Deflection at B)*Modulus of Elasticity*T2)/(2*B^2)

And calculating the safety factor by taking the Yield Stength divided by the Stress.

I have seen this equation, though, for cantilever beams, to calculate deflection:

However, for the equation of deflection at a specific point:

deflection = (Force*(B^2)*(3A-B))/(6*E*I)

I'm not sure how to calculate the "I" value. Why would there be inertia, and how do I solve it? When I look up equations, they seem to deal with rotation, and also require I plug in a width value for the plate. I didnt think width would be a factor for this?

Sorry for the long post, and any help is appreciated!

Edit: Seems I is mass moment of area. Would I use (1/12)bh^3? With b being the width (I didnt give this, assuming the plate is ~200 mm wide, and the height of the cut is "B", would the I value be I=(1/12)(200)(B)^3?

Last edited: Jun 3, 2010