It is common practice in simulation-supported component and assembly development to use standard material cards, some of which are already embedded in the simulation software. While this procedure usually leads to good results for isotropic, homogeneous materials and quasi-static loads at room temperature, requirement-specific material cards are indispensable for more realistic load scenarios (such as increased temperature or crash) or real material properties, such as temperature-, direction- or strain-rate dependent behaviour.
These anisotropic materials also include fibre-reinforced plastics, but in particular also many materials for additive manufacturing. The specific properties come either directly from the material itself (e.g. through a fibre reinforcement) or from the layer-by-layer manufacturing process. To reliably describe this anisotropic and possibly inhomogeneous material behaviour, LZS GmbH has developed a method for the creation of specific tailored material cards, which have been refined and tested in many projects.
In the day-to-day practice, we use this method to accurately describe the anisotropic, mostly non-linear deformation and failure behaviour of composites and additively manufactured structures. If necessary – for example in safety-relevant approval processes – this can be done in a certified test environment with comprehensive statistical validation. Often, however, a well-founded yet pragmatic scope of tests is sufficient for very good simulation results.
In both cases our activities are divided into experimental characterization and material card calibration. Here, the seamless interlocking of the testing and simulation team, as it is practised daily at the LZS, ensures a direct usability of our results, independent of the design system.
The at least direction-dependent elasticity and strength parameters required as a basis as well as the corresponding stress-strain characteristic function relations are determined within the context of a quasi-static basic characterization. In the example of additively manufactured structures, special effects such as the heat treatment state can also be incorporated into the test series (see figure). These values then are processed and provided for the simulation system used. If required, the experts at LZS GmbH also creates adapted material models and failure criteria in order to map customer-specific material behaviour.
Regardless of whether models implemented in the simulation software or customised models are used: After calibration on complex test specimens, the material card generated and validated by the LZS-Team is ready for accurate simulations.