Hello

The problem in this case of experiment and simulation differences still remains topical. Many of the reasons have already been investigated and measures have been taken, with most software having material with their mechanical characteristics in the elastic area and the plastic area. Frequently, experiments produce deviations from the tabular values ​​of the material. The reasons for this are mostly hidden in the material maker, the technology of obtaining, structural changes, and so on. For this, before simulating processes with software, it is good to conduct experiments to identify correct incoming paramters. Even the gimmick chart. Then there are also adequate results similar to the simulated model.

Success in research

Emil Yankov

There are several possible sources for the experimental-simulation mismatch, which seem to me more likely than a mismatch in the tension and compression behavior of Al 1100 H14, which I expect to be rather small, if it exists at all.

1.) Modelling the specimen undergoing indentation, geometry and boundary conditions:

The size of the simulation box (halfspace) should be sufficiently large both in width and depth directions to properly reflect the elastic effects.

If the halfspace is sufficiently large in lateral direction, the chosen boundary conditions (free or fixed) at the lateral boundaries do no longer play a significant role for the microindentation results. You can check that simply by comparing the results for different conditions.

If the simulation box size in depth direction is chosen too small, the (structural) stiffness of the indented halfspace will be larger than the real one, such that plastic yielding commences at an earlier stage of indentation.

2.) Finite element modeling:

In order to avoid artificial stiffening effects („locking“) it is recommended to use rather hexahedral/brick-type solid elements than tetrahedral ones, better quadratic shape functions (e.g. C3D20) than linear ones.

A sufficiently fine resolution not only of the indentation volume but also of its surroundings is crucial – you mentioned the measurement of mesh refinement in that region.

Hint: For the existing isotropy you can exploit symmetry and reduce the indented halfspace e.g. to one fourth, or even less, of course. (You could even exploit rotational symmetry.) Then a mucher finer discretization can be invested for the same costs compared to the full model.

- Modeling frictional contact comes on top of that, I would start out with a rigid indenter, zero friction.

3.) Material model.

The choice of isotropic elastoplasticity at finite strains seems to me adequate for that material and the deformation regime (large plastic deformations in the indentation zone).

Accurate material parameters in agreement with the experiments, i.e. yield stress and the hardening behavior. The hardening behavior will strongly influence the behavior of pile-up (low strain hardening rates) or sink-in (for large hardening rates).

Hope there is something helpful in it, good luck and have a great day ahead!

Hi!

You take the defining equations from the macroexperiment, and build a model for the microexpermint. The behavior of the material can be different at different scale levels.