Axisymmetric deformation in ANSYS

[atlamillia]

Homework Statement

A cylindrical sample of soft tissue, with diameter = 8 mm, height = 6 mm, is firmly
glued to two steel compression plates. Using axisymmetric
elements, find the force needed to compress the sample by 0.5 mm. For the purpose of
this problem you may assume that E = 1 kPa, ν = 0.45. If possible, verify your FE
solution using a back-of-the-envelope type calculation.

Homework Equations

This is a question about using ANSYS, so equations are not performed by hand.

The Attempt at a Solution

In the preprocessor, I add an element type, quad 4-node, change it to axisym.
I go to material properties, define a structural> linear> elastic> isotropic material with E = .001 (N/mm^2) and v = .45
I model a 4x6 area rectangle at 0,0.
I mesh it using meshing>mesh>areas>free, maybe refine it a little
In solution, I put a symmetric constraint on the side that intersects the y-axis.
I constrain the top and bottom from deforming by setting def x = 0
I apply a deformation of -0.5 to the top surface.
I solve...

The structure does not appear to deform at all!
The stress graph shows some extremely small (.1E-10) stresses. I know this is not correct.

 

[nvn]

atlamillia: Try these changes. Remove the symmetric constraint at the side that intersects the y axis. At the bottom end of the cylinder, add a constraint def y = 0. Rerun. Let us know what happens.

 

[atlamillia]

Thanks! It seems to be working now, and the values appear to be in the correct range. Looks like those axisymmetric modeling tutorials came back to bite me, I'm glad I asked.

Not nearly as important, but do you know offhand if there is a way to get ANSYS to tell me directly what load I would have to apply to get this deformation, or is it best to calculate it from the stress (what I was planning on doing)?

 

[nvn]

atlamillia: Perhaps see if you can display, plot, or read the y-direction element force at each y = 0 node or element. If so, add them together to obtain the total y-direction force on the bottom end of the cylinder. Or perhaps see if you can display, plot, or read the y-direction reaction force at each y = 0 node constraint (?). Please let us know what you find.

 

[DeeNos]

Based on the given information, it seems that the solution may not be accurate due to the extremely small stresses and lack of deformation in the structure. It is possible that the element type or material properties were not properly defined in ANSYS, resulting in an inaccurate solution. It may be helpful to double check the inputs and make sure that the model is properly constrained and loaded. Additionally, it may be beneficial to verify the solution using a back-of-the-envelope calculation, as this can help identify any potential errors in the ANSYS model. If the solution still seems incorrect, it may be necessary to adjust the model or seek further assistance.