At this point, two projects considering the determination of material data for FEA are presented. Our enhanced testing and evaluation method is able to optimize material data for a very wide range of application. To demonstrate this, the chosen projects are a cast aluminum for an elastoplastic material law and an elastomer for nonlinear viscoelasticity. Obviously the material properties differ very clearly:
- Order of magnitude of elongation at break of 1% and more than 100% respectively
- Inevitable material inhomogeneities due to the casting process leading to scattering of experimental data and accordingly a homogeneous material with large variations in viscosity.
- Damage and plasticity effects dominate or rather time dependence dominant.
The project was first shown in the ATZ - Automobiltechnische Zeitschrift, issue 03/2008.
Aluminium die casting for gear housings
Together with the University of Kaiserslautern and the GM Powertrain GmbH, the material parameters for elasto-plasticity have been determined using 3 different specimen geometries, namely a conventional tension rod, a perforated specimen and a side-notched specimen. See below the perforated specimen with a stochastic grey scale pattern:
To accurately determine the fraction of plastic deformation the specimens were initially charged only up to about 85% of the breaking load and relieved again (see chart at right). The measurement and evaluation method described on the side "material parameters" has been utilized. All experiments carried out, so all three specimen types and all retries have been considered within the global material data optimization. On the following animated GIF a verification of the calculated material data set can be seen; a comparison of the measured and simulated displacements of the individual differently loaded regions of a perforated specimen.
- point-and-click to animate
One can clearly see the good overall correlation, especially during and after the process of load relieving. The permanent deformations are represented at all relevant points of different stress conditions very well. This becomes even clearer when you look at the displacement over time, and force over displacement curves in detail at 5 representative nodes:
Elastomer in medical engineering
Together with the ECP Entwicklungsgesellschaft mbH, Berlin, the material data set for viscoelasticity was determined. Hereby the parameters for short term an long term relaxation were identified together with the parameters for the basic elasticity. Tensile tests have been conducted with perforated rectangular specimens. Hereby two different time domains have been considered. The following illustrations show the clamped specimen as well as the force-time curves of the two types of tests:
- point-and-click to enlarge
If you look at the corresponding verification, again a very good correlation between the measured and simulated displacement curves at almost all points on the specimen surface, is achieved. A separate analysis of the tests for the short-term and long-time behavior makes an even better fit possible, depending on if the one or the other material behavior in the later application is dominating.
- Point-and-click to animate
The performed FEM analysis using the determined material data set (18 material parameters for the elastic and viscous behavior) shows clearly how well the viscoelastic behavior can now be simulated. One can see the strain, the von Mises stress and the hydrostatic stress at maximum force (above) and at the end of the experiment (below).
- Point-and-click to enlarge
