ABAQUS Tension Analysis

Jorgen,

Thanks a lot for the swift response!

Yes, I do exactly as you described, although I am using CAE, so I field output the nodal reaction forces from the end face of the tube, and use a MATLAB script to sum them up over each time interval. The problem is that I get the same engineering stress, e.g. the same total reaction force on the end nodes regardless of whether or not there are holes in the tube.

In order to get the total strain of the tube, to match the tensile test, I am using the z-coordinate of the displaced face (displacing only z-direction), and calculate the change in length, and strains accordingly.

What I find very bothersome also, is that I can apply the same 1 million Pa load to the end face on the tube with and without holes, and I get nearly the exact same strains, no where near the lab results which reduce the nominal stresses by about 40% at 0.6 strain.

Thanks Again,

David

That sounds strange. Perhaps you can create a test case in which the holes are really big. That way you should surely get a different response. If not, you will know that there is something else that is wrong (perhaps with the data extraction approach).

- Jorgen

Jorgen,

I have tried exactly that, well similarly I tried patterning 6 holes instead of 2 and get no change in reaction force. This problem has been driving me crazy basically all summer as my job is to pattern holes with an optimal size and shape, and since I cannot match up a basic tensile test, no designing is getting done.

One of my professors suggested I use a fully linear elastic material model and try something similar, and if that works correctly, I would know it was the material model. Using that model, I tried using two holes, and was able to get an increase in compliance. Unfortunately I added 4 more holes to the fully linear model to see if it would further increase in compliance as it should, and it actually matched up exactly with the two holed fully linear model.

I am very new to FEM, and thought it was something wrong with the analysis, especially when I expected the reaction forces to be present in any cross-sectional slice, and they are only present on the B.C. nodes.

I can attach my input or CAE files once I get back to the lab.

Thanks A Lot for the Replies,
David

Still sounds strange. You should get the same reaction force at any cross-section. The reason I proposed the end sections with the BC nodes is that it is easier to extract the forces there. It is not necessary to use Matlab (although Matlab is really cool), you can actually use CAE to sum up the forces (which probably is faster).

If I were to guess, and this is just a guess, I suspect that you are doing something wrong when you extract the total reaction force...

- Jorgen

Jorgen,

If you could please tell me the basics of how to have CAE sum up the reaction forces for me that would be excellent, as I do not know how to do this, and have tried looking online before.

You agree that there *should* be nodal reaction forces in all nodes of the tube? This must be the case in order for it to be in static equilibrium (right?), which makes since, just like the tension is constant everywhere in a piece of pulled string.

Today, I tried outputting the data from some middle nodes, just by selecting them with a box arbitrarily. All of the reaction forces were 0!

Thanks Again,

David