Unwanted Node Movement in Abaqus

[Navigator14]

Hi, I am brand new to these forums and fairly new to abaqus as well.

I am doing a simple radial expansion on an axi-symmetric semicircle with a smaller semicircular hole in it. In order to do so, I created a datum CSYS that is cylindrical in nature but aligned with the global CSYS. In other words the R axis is the X axis and the T axis is the Y axis. After applying my displacement boundary condition to the inner semicircle to expand outward, I get the desired radial displacement, but I also get some varying motion of the nodes in the theta plane about 2 orders of magnitude lower than the radial displacement magnitude.

Any idea on why that might be? My sides of the semicircle are constrained with a XSym boundary condition and my outer surface of the semicircle is encastred. Is this due to the compression of the elements? And if so, is it unavoidable? I wouldn't want to create another boundary condition preventing theta-plane displacement?

I am uploading the input file as a .txt.

 

[Achy47]

Hello and welcome to the forums! It's great to see new users exploring the capabilities of Abaqus.

Based on the information you provided, it seems like the varying motion of the nodes in the theta plane could be due to the compression of the elements. When you are applying a displacement boundary condition to the inner semicircle, the elements in that region are being stretched and compressed, which can result in some small rotations in the theta plane.

One way to potentially reduce these rotations is to refine the mesh in the region of interest. This will allow for more accurate representation of the deformation and may help to minimize the rotation of nodes in the theta plane.

Another option could be to apply a boundary condition to constrain the nodes in the theta plane, such as an Rz boundary condition. This would prevent any rotation in the theta plane and may help to reduce the issue you are experiencing.

Overall, some level of rotation in the theta plane may be unavoidable due to the nature of the problem and the constraints applied. However, by refining the mesh and carefully selecting boundary conditions, you may be able to minimize the effects of these rotations.

I hope this helps and good luck with your analysis!