Constraint in finite element model?

[munilo]

I'm a new user of Ansys and I've run finite analysis of a 5 layered blocks model with different material properties. The model is 1/4 of the whole of blocks assembly. Fixed at translation Ux=0; Uy=0 which is the cut side of the model and constrained in all DOF at lower base part of the block. I've noticed a difference in displacement from 0.104mm to 0.106mm if constrained in all DOF at the uppermost component and the rest of the analysis results are all the same. How can you choose appropriate location to constrain a model?

Note:
Maximum size of assembled component 90mm x 48mm x 1.4mm
Minimum size 10 x 10 x .8

 

[asmenut]

When utilizing an FEA package, one must first understand that the software is meant to simulate real world conditions. The objective is to keep the model as simple as possible. Depending upon the boundary conditions and also the type of analysis being performed (i.e. Linear Static, Non-Linear, Thermal, etc.), the results will vary.

To answer your question, You must first ask youself how this part (component) will be functioning (real world). Once you have determined how this part will function, you will have a more concise direction as to where and how to place your boundary conditions. At this point, you can decide what avenue you would like to take, whether to utilize a nodal, elemental, or surface constraint. Remember that a finite element analysis records results based upon the nodes. Some packages such as NASTRAN, or PATRAN, will allow for the results to be viewed as an average of the nodes within the element, but the FEA still focuses on the nodes.

Remember to verify your results by calculation. This should give you the denominator for your percentage of FEA results to the theorectical.