Ultrasim^® Material Modeling and Data

The basis for an accurate material model is a proper experimental characterization. To this end, we utilize optical strain measurements in mechanical testing to obtain detailed information about the deformation state (deformation gradient) and to subsequently calculate stress measures appropriate for the specific material models. 

Furthermore, the mechanical response of polymeric materials is typically dependent on strain rate, temperature, moisture content (environmental climate) and, especially in short fiber reinforced plastics (SFRPs), on the direction of testing (anisotropy). A detailed material model requires experimental input for a combination of all these testing parameters which makes the characterization of polymeric materials particularly extensive. At BASF we spare no effort to perform all these required tests for feeding our models and providing our customers with outstanding data quality.

The main test that we utilize is the uniaxial tension test. One specialty of our setup is that it can measure up to very high strain rates of about 100 1/s which is key for calibrating material models for crash simulations. Depending on the material type we perform characterization according to specialized testing protocols which may also include compression tests (e.g. foams) and material testing under multi-axial loading conditions (e.g. elastomeric materials).

The main test that we utilize is the dynamic tensile test. One specialty of our setup is that it can measure up to very high strain rates of about 100 1/s which is key for calibrating material models for crash simulations. Depending on the material type we perform characterization according to specialized testing protocols which may also include compression tests (e.g. foams) and material testing under multi-axial loading conditions (e.g. elastomeric materials).

To facilitate our integrative simulation approach, it is required to characterize the material with respect to those properties that are modified during processing:

• In Short Fiber Reinforced Plastics this is the fiber orientation that evolves in the melt shear flow during the injection molding process. The anisotropic mechanical testing is thus further supported by a fiber orientation analysis derived by microcomputer tomography. This data provides valuable input for material model calibration of Short Fiber Reinforced Plastics.

• In foams this requires a characterization over density which, depending on the foaming mechanism, can be influenced by the local temperature (blowing reaction) and flow length. 

These standard measurements are complemented by specialized characterization for creep, fatigue, thermal and moisture expansion if the material is utilized in parts subject to corresponding load cases.

BASF’s engineering plastics are typically reinforced with short glass or carbon fibers. Since these fibers are much stiffer than polymers, they mainly determine the mechanical properties of the composite. Our material model for Short Fiber Reinforced Plastics (SFRPs) takes the fiber orientation as an input and most properties like material stiffness, strain rate dependence, stress and elongation at break become a function of fiber orientation. The fiber orientation at each location in the part is obtained by a preceding injection molding simulation which constitutes our integrative simulation workflow. 

The SFRP material model is highly versatile and covers, within a single parametrization, the main physical phenomena that these materials exhibit, including anisotropy due to fiber orientation, strain rate, temperature and moisture dependence. The material model can be calibrated for a large range of strain rates, facilitating crash (very high strain rates) but also creep (very low strain rates) simulations.

Furthermore, the SFRP material model can be applied in many kinds of static structural load cases including fatigue. A particularly challenging load case that can be addressed is the expansion and warpage of a plastic part due to a change in temperature and/or moisture content.

Ultrasim^® also offers material models for foams, like the reactive polyurethane Elastolit^®. These materials perform a foaming reaction which drives their flow in the mold. The reaction is temperature dependent and since the temperature distribution is heterogeneous in the mold this will also lead to a heterogeneous foam density in the part. Since the mechanical properties of foams are mainly determined by their density it is key to take this density distribution into account. Our Ultrasim^® material model for reactive PU foams can be parameterized over a wide density range (see figure). By performing a preceding foaming simulation, we obtain the density distribution in the part which can then be used in a structural simulation of the foamed part. See also our integrative simulation workflow for reactive PU foams.

Ultrasim^® provides hyperelastic material models for elastomeric materials that can be found in our Elastollan^® and Infinergy^® product families. The Ultrasim^® elastomer model supports static structural simulations including cyclic load cases by accounting for stress softening (Mullins effect) and hysteresis. For proper model parameterization, these materials are typically characterized under uniaxial and multiaxial cyclic loading.