Hi Steve,
As a test model for further research, we’re trying to model the following experiment: an indentation in the center of a circular latex membrane, constrained at the edge. The radius of the membrane is 30 mm, height is 0.15 mm. Indentation is realized by a needle, from which the tip can be assumed to have a radius of 0.5 mm. The latex specimen is assumed to be linear elastic, having following properties: Young’s modulus 1.5e6 Pa and Poisson ratio 0.3 (estimated from literature). When the indentation is 5 mm, the measured reaction force on the needle is approximately 180 mN.
As a first approach, the indentation was modeled by attaching a cubical rigid body (basis 0.5 mm) onto the center of the membrane. Next, the displacement of 5 mm on this rigid body is imposed, and the resulting reaction force on the rigid body is the output parameter of interest. The problem converged well (using more nodes resulted in converging to a constant reaction force), but the final value differs almost a factor 100 with the experimental value. Moreover, the resulting indentation-force curve is linear, while the experiment shows, as expected, a clearly nonlinear behavior.
Further investigation didn’t result in a more realistic solution: placing the rigid body in the membrane instead of onto it using the tubal geometry (file1.feb), using shell elements by use of FEBio version 1.1 (file2.feb) or applying a pressure and taking a look at the resulting displacement all resulted in a significantly wrong output.
As an additional test model, we tried to model the bending of a rectangular plate using shell elements. A quick look at the resulting deformation shows that there seems to be something wrong (as posted on this forum earlier).
For comparison, we modeled the above mentioned problem in the Abaqus FEM-software packet, giving us results far more in agreement with the experimental data.
You have any suggestions, remarks, … to obtain a more realistic solution?
Thanks in advance!
Cheers,
Joris and Jef
As a test model for further research, we’re trying to model the following experiment: an indentation in the center of a circular latex membrane, constrained at the edge. The radius of the membrane is 30 mm, height is 0.15 mm. Indentation is realized by a needle, from which the tip can be assumed to have a radius of 0.5 mm. The latex specimen is assumed to be linear elastic, having following properties: Young’s modulus 1.5e6 Pa and Poisson ratio 0.3 (estimated from literature). When the indentation is 5 mm, the measured reaction force on the needle is approximately 180 mN.
As a first approach, the indentation was modeled by attaching a cubical rigid body (basis 0.5 mm) onto the center of the membrane. Next, the displacement of 5 mm on this rigid body is imposed, and the resulting reaction force on the rigid body is the output parameter of interest. The problem converged well (using more nodes resulted in converging to a constant reaction force), but the final value differs almost a factor 100 with the experimental value. Moreover, the resulting indentation-force curve is linear, while the experiment shows, as expected, a clearly nonlinear behavior.
Further investigation didn’t result in a more realistic solution: placing the rigid body in the membrane instead of onto it using the tubal geometry (file1.feb), using shell elements by use of FEBio version 1.1 (file2.feb) or applying a pressure and taking a look at the resulting displacement all resulted in a significantly wrong output.
As an additional test model, we tried to model the bending of a rectangular plate using shell elements. A quick look at the resulting deformation shows that there seems to be something wrong (as posted on this forum earlier).
For comparison, we modeled the above mentioned problem in the Abaqus FEM-software packet, giving us results far more in agreement with the experimental data.
You have any suggestions, remarks, … to obtain a more realistic solution?
Thanks in advance!
Cheers,
Joris and Jef
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