I got your calculation Harryvl into a spreadsheet the deflections mm come out very close probably spreadsheet rounding errors.

Is there a point where the deflection shows it will proabably start to show signs of breaking or a point to avoid?

- tubecalc.png (77.18 KiB) Viewed 407 times

I got the updated specifications from dragonplate and the 3 loads I wanted to try.

That way I setup the spreadsheet and it is easly shared and tested. Also if I have to make design changes I can.

Here are the tube specifications do I put density in this equation somewhere EL?

"Hi I got factory specs that could go into kicad fem. I figured it would help even if I tried a hand calculation.

density ~1700 kg/m^3

modulus ~34 Msi (~230 GPa)

poisson ration 0.2"

"The force on other systems is 3100 newtons.

1/16 of that 194 newtons

and 620 newtons would be tests I would wonder how the tubes would be effected.

the material properties would be

density

460 kg/mm^3" So the spreadsheet should allow me to test all 3.

HarryvL wrote: ↑Thu Aug 09, 2018 9:51 pm

so ....

With E= 234422 N/mm^2, OD=25.4mm and ID=20.3mm, EI=E*π/64 *(OD-ID)^4=234422*π/64*(25.4-20.3)^4 = 7.66E6 Nmm^2

All your tubes have the same EI, but you have 2 lengths (pcft_24: L=610mm and pcft_98: L=2489mm).

Finally you have put (

only!!) 1 N of load on each element, giving a uniformly distributed load of pcft_24: q=1/610=0.00164 N/mm and pcft_98: q=1/2489=0.00040177 N/mm

Putting it all together, the deflections of your tubes are:

pcft_24: u=0.00164/8*(610)^4/7.66e6=3.7mm

pcft_98: u=0.00040177/8*(2489)^4/7.66e6=252mm

I am a bit rusty, so it is quite possible I made a few mistake here ... but is only to demonstrate that 3D elements make no sense for the full model.