Efficient Calibration of Material Cards using Microscale Models

Project Revit: Calibration of Material Cards for FRP Materials Based on Real and Virtual Micro Tensile Tests

In the REVIT project, an ITWM team is working together with the Fraunhofer Institute for Mechanics of Materials IWM to create microscale models – with the help of a few physical measurements and CT scans. Based on these, material cards for the mechanical characterization of fiber composites are calibrated. In the future, microtensile tests, among other things, are to expand and make the calibration of the microscale models more precise. 

Fiber-reinforced composites (FRPs) are being used more and more frequently in areas such as the automotive industry or lightweight construction, as they can be produced quickly and offer a high degree of design freedom. Due to the short process times, fiber-reinforced injection molding and compression molding compounds made of short or long fibers in particular are widely used. Quality assessment is highly complex and requires so-called »material cards« from which behavior parameters of the FRP for the respective component can be seen. Calibrating these usually requires a large number of expensive laboratory tests, which is why medium-sized companies have so far often had to rely on less precise material cards with low accuracy. The REVIT project is financially supported by the funding program for rapid SME-oriented in-house research in order to offer SMEs a much more efficient and cost-effective solution with this approach.

The behavior of FRP components under load depends on the orientation of the fibers within the plastic material. Therefore, it is necessary to determine the dependence of the material behavior on the fiber orientation as precisely as possible. This is already possible today, but usually about 250 material tests have to be carried out for this purpose. We – ITWM experts from the departments »Flow and Material Simulation« and »Image Processing« as well as a team from Fraunhofer IWM – are working on replacing this process by a few physical tests in combination with virtual measurements.

Segmented Micro-Sample Scan
© Fraunhofer ITWM
Segmented micro-sample scan for the development of components made of fiber-reinforced plastic (like the buckle of a lanyard here). The glass fibers can be seen in gray, and a matrix material (polypropylene) in green.

Microscale Models as a Basis for Material Cards

As a basis for this new approach, we create a microscale model using the software »FeelMath« – an analysis software developed at Fraunhofer ITWM for the calculation of effective mechanical and thermal properties of microstructures. In the microscale model, the fibers and the matrix material are geometrically resolved. With the help of this model, virtual experiments can subsequently be carried out in order to finally calibrate the material cards required for component design.

The creation of the microscale model succeeds with the help of:

  • DMTA measurements (dynamic mechanical thermal analysis)
  • Data sheets containing information about the fiber geometry
  • μCT scans on test specimens

Improving the Previous Approach by Micro-tensile Tests

To further increase the accuracy of our methodology, we are currently working on extending the measurements on the pure matrix material (in which no fibers are present) by tensile tests on microsamples taken from the composite. In exemplary cases, these tensile tests will be recorded with a CT scanner throughout the run. In this way, we can see changes in the fiber arrangement. The parameters that can be derived from this will also be validated by the measurement methods mentioned above. 

Saving Costs and Time With Virtual Twins

This procedure corresponds to about a quarter of the effort of traditional testing methods. The objective of the project is to achieve a comparable workload of 20 to 50 traditionally tested samples. With the calibrated micromodel, almost any number of virtual experiments can be carried out cost-effectively. This enables companies to reduce the purely experimental effort by up to 80 percent compared to the traditional methodology.


Our Partners in the Project

Fraunhofer Institute for Mechanics of Materials IWM, Dr. Jörg Lienhard


Project Duration and Funding

The project is funded as part of the Fraunhofer-internal program for rapid SME-oriented in-house research. It is scheduled to run for two years from July 2020 to December 2022.