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Excessive element distortion under high indentation depth
Dear everyone,
I am new to Abaqus and I have been struggling for the past 3 months about this issues I am facing on my modelling...
Basically I am trying to simulate an indentation experiment on a biological tissue, with glass capillary as the tool for indentation. However, the tip of the capillary is very small compared to the actual size of the tissue, i.e. diameter of the capillary tip is ~0.7cm, the diameter of the tissue under indentation is ~50cm and the length of the tissue (modelling the tissue as a cylinder now) is ~500cm. The real experiment shows that the indentation can easily go to 16cm with NO penetration. However, building a model to simulate this indentation has been a headache for a past few months. Here are the approaches I have tried until now:
1. I use a global seed size of 3cm, and choose Tet linear (C3D4) to mesh the cylinder. And build the geometry as close to the real experiment, where there are 2 walls against the tissue under indentation. Please refer to the attached for the experimental geometry. The material properties for the tissue currently is 'Homogeneous, Isotropic' with a Young's modulus of 0.8MPa and Poisson Ratio of 0.48 (to simulate something like rubber). The simulation can go up to 16cm indentation. However, as shown from 'LD' and LD1' pictures, the distortion is very local and the element under indentation has a excessive dostortion.
2. I have tried all the other meshing scheme available from Abaqus 6.12, including the Hex (linear and Quad), Tet (Quad), Wedge (Quad). All these schemes cause the solution failed after along time of running. However, theory shows that Hex (Quad) and Tet (Quad) are the best schemes to simulate and estimate the stress?
3. I have also tried to assign local seed size (after partitioning the cylinder) so that the density of mesh close to the indentation area is very high. Please refer to 'Small Mesh' and 'Small Mesh 1' for the results. These methods usually takes a long time to run and always fail during the initial time increment, i.e. failed for small indentation depth.
With the approaches I have tried, my questions are:
1. Why only Tet Linear meshing scheme can simulate the experiment, but not the Hex/Tet Quad as I suppose Hex/Tet Quad can do a better job normally?
2. Why it looks like an element size of 3cm is the only choice, increasing and decreasing the global seed size can fail the solution and assigning different seed size on different parts of the cylinder can also fail the solution?
3. Is there a better way for modelling so that the deformation is more GLOBAL rather than the current excessive local deformation on the element under indentation?
I would like to take the chance to thank you all in advance in helping out! Really appreciated!
Thanks,
Dave
Attachment | Size |
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LD.JPG | 210.99 KB |
LD1.JPG | 98.47 KB |
Small Mesh.JPG | 274.14 KB |
Small Mesh 1.JPG | 112.29 KB |
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