Fast, versatile and accurate: determining materials data for forming process simulations in the Virtual Lab
(July 4, 2017) Sheet metal materials are often stressed to their limits during the forming process. Computer simulations are used to test how far it is possible to go in the production stage. However, the simulations are only as exact as the data upon which they’re based. A team at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg has now developed a virtual test laboratory that allows for the examination of metal materials at different load states and for the determination of precise mechanical data.
The mechanical properties of sheet metal materials are directional: their deformation behavior and strength differ significantly depending on the viewing direction, for example in the direction of rolling or transversely to it. This being the case, numerous complex load tests have to be carried out in order to obtain the necessary material data. These serve as a basis for predicting the behavior of sheet metals during the forming process.
Traditional laboratory tests are time and cost intensive, requiring different experimental setups and material samples for each load case. Although important for computer simulations concerning the manufacturing process of components, it is not possible to analyze all possible load states of sheet metals. As an example, conventional tests reach their limits when it comes to determining the behavior of sheet metal materials in the direction of their thickness: in this direction, a sheet thickness of one to two millimeters is not sufficient to allow preparation of samples for tensile testing.
Tensile tests in the direction of sheet thickness
“In our virtual lab, tensile tests in the direction of thickness are no problem,” says Dr. Alexander Butz, project manager in the Forming Processes group at the Fraunhofer IWM. “Likewise, all other load states can be tested quickly and flexibly, meaning that we are able to provide component manufacturers with much more detailed material data.”
To this end, with the help of a few standard experiments, Butz and his team first create a simulation model of the material’s microstructure - down to the crystalline structure - with which the physical mechanisms during deformation are described. This allows them to computer generate all the required tests and to draw reliable conclusions about the macroscopic mechanical properties of the material. “The method is not new. What is new is that we have developed an automated workflow that saves time by allowing us to run the tests virtually,” Butz explains.
As it is possible to perform many virtual tests in a short time frame and because the underlying microstructure model is quite precise, the results from the virtual lab allow what is known as a material card to be described much more accurately than with traditional tests. The virtually obtained data can be processed by component manufacturers in the same way as data obtained through experiments. In addition to simulations for component production, this also applies to simulations for predicting component behavior and its lifetime expectancy.
Critical points in the microstructure can be systematically investigated
An additional advantage: “Critical points where components are frequently damaged during production can be isolated and the microstructure systematically examined as if with a virtual microscope. We thus gain insights into ways of improving the processing chain,” Butz says.
The virtual test laboratory is especially interesting for the lightweight construction industry because it strives to use as little material as possible – which results in the material being subjected to high stress levels. “Overall, our development is exciting for those who require very precise input data for process simulation and component design, for example component manufacturers in the automotive and aerospace industries, or in additive manufacturing.”
Dr. Alexander Butz
Phone +49 761 5142-369