FreeBody

[Capko]

Hello everyone,

I'm having some troubles with the Abaqus' FreeBody tool. When I cut my model, the value of the resultant force in the section change if I change the cutting angle and it shouldn't.

Why is this happening?

 

[StefCon]

Hi,
Are you doing a free cut with a plane? I think the forces for that method is calculated based on element stresses. Even a round bar with a partition can give you maybe 5-10% error using the free cut method.

I got the best results (results which I trust) with activating NFORC (field output), creating cuts on element faces (requires partitioning of part).

If you have time, maybe you could try it out for a given angle or two, and see if it makes a difference for you.

Cheers!

 

[Capko]

Thaks for you help StefCon!

Yes, I'm using a free cut with a plane and as you said it's normal to find some errors in the results. The problem here is that I'm finding errors one order of magnitude (even two!) higher or lower so something strange is happening...

 

[StefCon]

Hmmm... That is a lot.

Does your model have multiple load paths?
Are elements hidden in places you don't wanna check (so they are not accidently included in results)?
Does the plane pass through contacts?
Is your element mesh density sufficient(maybe a singularity make the stress go mad)?
Is the total force correct?

I hope you find out the cause. I would like to know.

 

[Capko]

Actually, just to see what's happening I've made a quite simple model: a box with an applied load in one side and a encastre in the other one.

I cut the box just in the middle, I plot the FreeBody Loads by components and, as expected, I see the resultant load in one of the axes that corresponds with the applied load and almost 0 in the others.

If I maintain the same point but I change the cutting angle, the values of the others two axes starts to change but the resultant value remain the same.

 

[IceBreakerSours]

Fundamental stuff: The length of a vector (resultant) MUST never change just because you are looking at it differently; a vector is a geometric entity whose existence is independent of any coordinate system. However, a vector's components can change depending on the observer.

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