If I have an acrylic (plexiglass) panel, how can I compute how thick it must be to resist bending.

So, for example, if I have a sheet that is 24" x 36" and supported by the edges only (such as in a large light fixture), how thick does the sheet have to be to be self-supporting so that it does not bend in the middle?

  • 2
    $\begingroup$ The answer depends how it is fixed at the edges. Also, any thickness of panel will "bend in the middle" - the question is how much bending is unacceptable for what you want to do. $\endgroup$
    – alephzero
    Jul 21 '21 at 0:48

you need to have your acrylic material properties data sheet, such as its modulus of elasticity, E and its max stress, $\sigma s$, and poisons ratio. Usually the acceptable deflection, y ranges between $y<L/180, \ or \ y<L/360$

Then you try different thicknesses, t, till you get the smallest t with acceptable deflection.

Referring to Roark’s Formulas for Stress and Strain, by WARREN C. YOUNG RICHARD G. BUDYNAS seventh edition table 11.4 pp 507 For a rectangular plate simply supported at the edges uniformly loaded with q:

$$y_{max}= \frac{-\alpha qb^4}{Et^3}$$

$$ \sigma max = \sigma b = \frac{\beta qb^2}{t^2}$$

The coefficients, $\alpha \ and \ \beta $ are shown in the following table.


  • 1
    $\begingroup$ Might need to add that the plate dimensions are $a \times b$ with $a$ the long dimension $\endgroup$
    – D Duck
    Jul 21 '21 at 8:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.