Calculate the thickness of a plate to withstand a specified uniform pressure

[Plat]

In exploring the feasibility of constructing a vacuum chamber, I am trying to calculate the thickness of rectangular polycarbonate sheet needed to withstand 100kPa of pressure, given dimensions of 30.5cm by 61cm (12 by 24 inches) and clamped edges.

I have found some calculators that will tell me the deflection given different thicknesses, but what I really need to know is whether actual failure will occur and how much safety margin in thickness will be required to reduce this possibility.

I have found values of Young's modulus to be 13.5 - 21.4 GPa and Poisson's ratio to be 0.3182 - 0.3487 for polycarbonate.I am aware that constructing and using such a chamber presents safety risks and, if I do it, I want it to be as safe as possible and take all responsibility for it.

 

[Dr.D]

Will this be used just once, or will it be cycled? (Is fatigue an issue or not?) What do you know about the stress-strain curve for this material? Is it brittle, ductile, or what?
You say clamped edges, but absolute rigid clamping is a fiction; just how clamped will it be?
There are a thousand questions that need to be addressed, and this is not a good to start your engineering practice.

 

[Plat]

I agree however I am not an engineer, that's why I'm asking.

 

[Plat]

The full thickness of the sheet will be comprised of two thinner sheets solvent laminated together. Thus, the chamber will have an inner and outer layer of polycarbonate, with the inner and outer layers alternately overlapping each other at the corners so that the force under pressure is never held only by a bond. The front and back ends will be capped by double-layer sheets which completely overlap the edges where they are located.

So the edges will be solvent-bonded together.

For example, assuming a thickness of 0.5" for each single sheet, the dimensions of each sheet needed to fit together as I have described are as follows:

In inches:

12 x 18 Quantity = 4
13 x 18 Quantity = 4
13 x 14 Quantity = 4

I have calculated a maximum deflection of 1.6mm for a 30cm x 45cm x 2.54cm sheet under 100kPa with simple edge support, which seems reasonable. With my fixed edges, it should actually be much less than that.