Hi Daeho,
As per my understanding, you are encountering issues when you are calculating strain for middle nodes of the model. The issue you're encountering is related to how strain values are interpolated and averaged across elements in finite element analysis (FEA). In particular, quadratic and tetrahedral elements (which have both corner and mid-side nodes) present unique challenges when averaging strain values at nodes.
To obtain strain values at the nodes, the strain values at the integration points are interpolated to the nodes. This interpolation is done using the shape functions of the elements. Mid-side nodes in quadratic elements are not as straightforward as corner nodes. They are influenced by the strains from the adjacent elements differently due to ther position and nature of the shape functions.
Possible reasons for discepanices:
- The interpolation of strains from integration points to nodes can introduce errors, especially for mid-side nodes where the shape functions are more complex. Use higher-order interpolation methods to transfer strains from integration points to nodes. This can help reduce errors, especially for mid-side nodes.
- The method used to average the strains at shared nodes can significantly impact the results. A simple arithmetic average may not always be the best approach. Instead of a simple average, I suggest you use a weighted average based on the contribution of each element to the node. This can be based on the volume or area associated with each element.
- Ensure that the mesh quality is high. Use mesh refinement and optimization techniques to improve element shapes.
Hope that helps!
Balavignesh
