Help validating FEA results.

[Tudor Miron]

Hi,
I'm new to FEA and just started learning ANSYS. For the beginging I made very simple model - a box like structure with 40"� length tubes rectangle top and bottom and 10"� height. This is made of 1"x 0.049" steel tubes

I assigned constrains (translation but free rotation like ball joint) to one side 4 corners and applied equal and opposite (220lb) loads to opposite side corners. Those corners displaced 1.166"� in opposite directions. I calculated torsional stiffness to be 219lb-ft/deg by

Ts= F x d / 0.5(Фd+Фp)) x 0.083 where F = load, d = distance (40"�), Ф = twist angle. (X 0.083) - I did to convert from "� to ˜
After this I added two diagonals to stiffen the sides (after reviewing results of first run it seemed that they where most stressed.) Than same constraints and same loads.

Displacement of corners (to which force was applied) was reduced DRASTICALLY! It was only 0.067"�!
And torsional stiffness of 3969ft-lb/deg
My question is how does this results (displacement and torsional stiffness) sound to you? Best way would be to simply fab the same "frame"� and test it myself physically and I would certainly do it but I will have this possibility no earlier than march.

I wish I could post an image of this thing so it could be more evident what I mean. My limited English doesn't help here.

Could anybody duplicate this very simple analises so to validate my results? This should not take more than 10-15min to do.

Thanks you
Ted

[Tudor Miron]

Hi,
I'm new to FEA and just started learning ANSYS. For the beginging I made very simple model - a box like structure with 40"� length tubes rectangle top and bottom and 10"� height. This is made of 1"x 0.049" steel tubes

I assigned constrains (translation but free rotation like ball joint) to one side 4 corners and applied equal and opposite (220lb) loads to opposite side corners. Those corners displaced 1.166"� in opposite directions. I calculated torsional stiffness to be 219lb-ft/deg by

Ts= F x d / 0.5(Фd+Фp)) x 0.083 where F = load, d = distance (40"�), Ф = twist angle. (X 0.083) - I did to convert from "� to ˜
After this I added two diagonals to stiffen the sides (after reviewing results of first run it seemed that they where most stressed.) Than same constraints and same loads.

Displacement of corners (to which force was applied) was reduced DRASTICALLY! It was only 0.067"�!
And torsional stiffness of 3969ft-lb/deg
My question is how does this results (displacement and torsional stiffness) sound to you? Best way would be to simply fab the same "frame"� and test it myself physically and I would certainly do it but I will have this possibility no earlier than march.

I wish I could post an image of this thing so it could be more evident what I mean. My limited English doesn't help here.

Could anybody duplicate this very simple analises so to validate my results? This should not take more than 10-15min to do.

Thanks you
Ted

[Matt Gignac]

This makes sense. In the first scenario, the bars resist the torque by bending, which isn't how they should be loaded. In the second cases, the diagonal braces are loaded in tension or compression, which is how they should loaded.

Matt Gignac
McGill Racing Team