# Cantilever beam deflection

• 05-24-2016, 05:53 PM
PS2112
Cantilever beam deflection
I need to calculate the maximum beam deflection on a horizontal beam fixed at one end.

My beam is a round carbon fibre tube 80mm outside diameter and 74mm inside diameter. The tube is 2 metres long. At the free end is a weight of 5kg.

Please show me how to do this.
• 05-24-2016, 06:49 PM
Kelly Bramble
See: [B][URL="http://www.engineersedge.com/beam_calc_menu.shtml"]Beam Stress and Deflection Equations and Calculators[/URL][/B]
• 05-25-2016, 03:36 AM
Cake of Doom
As long as you know the E and I values (It can be worked out arithmetically), it's pretty straight forward from there.
• 05-25-2016, 10:32 AM
PS2112
Thanks, I have found the correct calculator and have requested the E value from the manufacturer. Sorry but I don't know how to arrive at an I value. I'm assuming it is related to the cross sectional area but confused by the unit mm^4. Please help.
• 05-25-2016, 11:11 AM
Kelly Bramble
See [B][URL="http://www.engineersedge.com/calculators/section_square_case_12.htm"]section properties round tube[/URL][/B]..

or
Section properties calculators and equations[/URL][/B]
• 05-25-2016, 11:52 AM
PS2112
Thank you, I'm beginning to see that Engineers Edge is very comprehensive and seems to have every possible resource :)

Right, I've got the I value sorted thanks. No email back from the manufacturer about the modulus of elasticity, and as it is past 5pm now, I won't get that till tomorrow. I'm eager to play with these figures tonight and hoping someone can provide me with a ball park figure to use for E on each size of tube. Then I can at least get some provisional deflections tonight. I'm hoping for a deflection well under a millimetre, but if it is a lot more will have to seriously reconsider my design and materials.

Thanks for all your help, as I have not found the need to work with such calculations since my college days nearly 40 years ago.
• 05-25-2016, 05:27 PM
PS2112
I have now found an E value on a different manufacturers website for a similar carbon fibre tube that allows me to use the calculator to make a reasonable estimate.

If my beam was pointing at a different angle from horizontal, say 45 degrees up, would I be correct in thinking that the deflection could be multiplied by the sine of the angle? So at 45 degrees the deflection would be...
sine (45) = 0.707 x (horizontal deflection)
• 05-25-2016, 06:54 PM
Kelly Bramble
[QUOTE=PS2112;12367]I have now found an E value on a different manufacturers website for a similar carbon fibre tube that allows me to use the calculator to make a reasonable estimate.

If my beam was pointing at a different angle from horizontal, say 45 degrees up, would I be correct in thinking that the deflection could be multiplied by the sine of the angle? So at 45 degrees the deflection would be...
sine (45) = 0.707 x (horizontal deflection)[/QUOTE]

No... See: [url]http://www.engineersedge.com/beam_bending/combined-stress-1.htm[/url]

or just scroll down and see all options...

• 05-26-2016, 02:58 AM
Cake of Doom
As Kelly points out: No. Members under loading act differently once angles become a factor.
• 05-26-2016, 08:24 AM
PS2112
Thanks, but I have looked through all the options and can't find a calculator that allows me to change the angle of the beam. Could you give me a link straight to it please.
• 05-26-2016, 08:54 AM
Kelly Bramble
[QUOTE=PS2112;12371]Thanks, but I have looked through all the options and can't find a calculator that allows me to change the angle of the beam. Could you give me a link straight to it please.[/QUOTE]

I think this is the one you're looking for...

[url]http://www.engineersedge.com/beam_bending/combined-stress-1.htm[/url]