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# Output Vector

## Output Vector

(OP)
Hello,

I try to get a better understanding of the meaning of the output vector for stresses in femap, and I'm a bit confused now!!

With femap, we can get for a plate element, X normal, Y normal and XY shear stress. So I believe these are the components of the stress tensor.
But X and Y are relative to each element right? (X direction is from 1st to 2nd node).

So what I don't understand is when femap gives X normal stress, what is X? is it the global CS?

Also if the stresses are averaged from adjacent nodes, but the stresses are from elements which have different orientation; how accurate this is?

I have probably missed a point because I now don't know how to interpret the output from femap!

### RE: Output Vector

X and Y are in element axes ... watch what happens when you change an element's axes. The FEA is expecting you to understand your model.

### RE: Output Vector

(OP)
Thanks rb1957. So I have adjacent elements with a different orientation, then how relevant would be the contour plot?

Also, when the average of the stresses computed from surrounding nodes is done, it seems that regarding the element orientation, the values picked up would not be the same.

So I 'm a bit puzzled about the consistency of the results now

### RE: Output Vector

Hi

First, you can set the element orientation using Modify-Update Elements-Material Orientation
Second, you can check the orientation with View-Options-Labels....-Element Material Direction

There is several parameters to "play" with and like rb1957 said, you need to understand your model. To simply accept the defaults can result in strange things.

Thomas

### RE: Output Vector

(OP)
thanks a lot; so now I know that the contour plot has to be interpreted with care especially if the elements have very different orientation.

Is it the same for the principal stresses? I guess in that case the orientation of the vector is given by the angle giving no shear.

Finally, at a given element, let's say a distorted quad (not a perfect rectangular as in books). we have sigmaX, that gives traction. so if we want the normal force, how is calculated, what is the cross section taken as is varies along the element?

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