# Foo - How do you model torque in FEA?

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View Full Version : How do you model torque in FEA?

slvoid
08-11-06, 10:01 PM
I've got a model which is basically a motor with a square armature driving a gear box with a square lug and I need to model the forces in FEA. The only problem is that the force distributes from 0-full from the middle of the side of the square lug to the edges on all 4 sides and there's no way for the ansys package I'm using now in autodesk inventor. I can apply a normal force onto the side but I end up having to build a stepped pad onto the sides of the lug and then approximating the forces onto the steps. So i'm like basically setting up a finite analysis while preparing the mesh for the actual finite analysis, which is pretty messed up.

Michigander
08-11-06, 10:04 PM

I would shoot it and buy a new one.

slvoid
08-11-06, 10:07 PM
Ah... makes sense.

iamlucky13
08-12-06, 02:55 PM
Sorry...I haven't touched ANSYS in over 2 years. It seemed to me that ANSYS had a standard torque case in it's library. Why does the force increase like you describe? You can't get a reasonable approximation by placing shear forces on the faces of the lug?

I assume this is a part too complex to simply consider on it's own with an calculate the shear stress at the base...

jyossarian
08-12-06, 04:07 PM

slvoid
08-14-06, 12:24 PM
Well the lug itself is easy enough to calculate, it's not the shear it's the deformation and stresses on an adaptor around the lug, which is pretty complicated in geometry.
I guess an easier way to break it down and ask is to ask how I would model the forces exerted on a bolt interface in FEA on a plate of metal.
I'd have to create a temporary pad to simulate the forces exerted onto the plate by the bolt by grounding that pad right?

Falanx
08-14-06, 12:49 PM
Trust me. FEA is not as accurate as people would like to think, especially on thin components were things like inclusions and processing textures will alter the response to a normalised stress field.

Cover the thing in strain guages, build it and give it some hammer. You'd be better off.

slvoid
08-14-06, 01:24 PM
The thing is actually a big chunk of aluminium. Given the right modeling, FEA can do a pretty good job. It's often not economical to build dies for 10 different designs, even soft dies, to build prototypes to test when you can narrow it down to 1-2 before live testing. The problem with strain gages is that it doesn't always have enough resolution to capture the minor details. Strain gages are fine for simple or large geometries where you have relatively finite sampling points. A photoelastic test would be better but again, no live samples. Now if I can just figure out how to set up the analysis correctly, it should point me in the right direction.

Siu Blue Wind
08-14-06, 01:31 PM
ha ha. Didn't think you'd do it, Wong. ;)

jsharr
08-14-06, 02:10 PM
Awww, come on guys, it's so simple. Maybe you need a refresher course. Hey! It's all ball bearings nowadays. Now you prepare that Fetzer valve with some 3-in-1 oil and some gauze pads. And I'm gonna need 'bout ten quarts of anti-freeze, preferably Prestone. No, no make that Quaker State.

SaabFan
08-14-06, 02:26 PM
Last night I slipped on my tub and fell, and dreampt up the answer to your question. Here, I drew a picture:

slvoid
08-14-06, 02:38 PM
Last night I slipped on my tub and fell, and dreampt up the answer to your question. Here, I drew a picture:

400 watts??? Where am I going to get that kind of power?

Falanx
08-14-06, 02:40 PM

slvoid
08-14-06, 03:28 PM