Material Design with DIGIMAT

DIGIMAT applies the systematics of „top-down“ modeling which means that continuum mechanics based methods are used to describe the material microstructure. Among these mathematical mean field homogenization is implemented in the software (digimat-MF). Also a generator for arbitrary material microstructures can be found (digimat-FE). The stochastic models produced with this tool can be homogenized in a subsequent step using an external FE solver like ANSYS.

The application of homogenization methods can be found in different areas. Material designers are expert users and seek for a deep understanding of interactions within the material and their influence on the overall properties. Therefore they need DIGIMAT in the context of basic research and apply it as a virtual material laboratory. But DIGIMAT also offers homogenization as an easy to use tool for the everyday application in the engineering business. In this context the influence of the processing on the material properties as varied by changes in the local microstructure of parts is considered.
For fiber reinforced plastic parts which are produced by injection molding DIGIMAT enables the use of constitutional laws especially suited for this complex material. Such descriptions are not only sensitive to the local orientation of the glass fibers in the part but also reflect the nonlinear strain rate or temperature dependent behavior of the material. In addition failure indicators can be defined and uses in ANSYS or LS-DYNA. The real strength of this approach is the automated coupling between results of injection molding simulations and the structural mechanics analysis. This way the influence of the processing of the part directly becomes visible in FEM calculations.
With the database approach as offered by digimat-MX the user can decide by himself whether he likes to be the materials expert or rather focuses on the design of the part by simply choosing materials models which are already prepared for him.

Digimat-FE serves as a module for the stochastic generation of the geometry of a specific microstructure. Through the choice of different parameters and boundary conditions arbitrary microstructures can be created. The generated models are investigated in a subsequent step using FE methods as implemented in ANSYS or LS-DYNA. Digimat-FE offers geometry export in different CAD formats (IGES or STEP). Based on these CAD data homogenization is carried out using the external FEM solver.

The FE analysis for example shows the influence of traction or shear on the stress and strain in the material itself. The distribution of these quantities can be investigated in detail. This approach offers the possibility of the optimization of material properties or it can be used for a deep understanding of mechanism within the material such as fatigue under load.

Furthermore, homogenized material properties can be gained through the application of FEM. The calculated stiffnesses can be used in the next step for the macroscopic simulations of parts built from microstructured materials.

Digimat-to-CAE bundles all interface capabilities of DIGIMAT. They are based on the mathematical homogenization as implemented in digimat-MF. Digimat-to-CAE directly links this method into the user defined subroutines of FE solvers like ANSYS or LS-DYNA. With this technology DIGIMAT offers a real bi-directional multiscale coupling between the micro and the macro scale. Changes in the material microstructure immediately become visible on the macro scale. For example, the local fiber orientations in a reinforced plastic part will significantly influence the response of the overall device under load.

In this context digimat-to-CAE is more than just a material interface. It fully couples injection molding simulations and FEM. In injection molding the flow of the mold determines the local microstructure of the material in the produced part. Digimat-to-CAE reads in the fiber orientation as given by injection molding software (Moldflow, Moldex3D or 3DSigma). Based on this information for each element of the FE model an individual material behavior is calculated. This scenario mirrors the situation of the real part as closely as possible.

The effect on the FEM results is profound. Differences in the stiffness of the part as resulting from variations of injection points in the processing are reflected according to experimental results. Extremely critical areas like welding lines are visible in FEM and can be investigated under different loading conditions.

From the application point of view coupled simulations with DIGIMAT/ANSYS are very easy. The coupling is introduced into ANSYS by using the integrated ANSYS workbench wizard. Out of the ANSYS workbench environment this tool leads the user through all important stages of the setup including the mapping of fiber orientation data from injection molding onto the structural mesh.

Different FEM disciplines deal with different types of meshes. This is especially true for injection molding simulations and structural FE and makes mapping an essential part of a coupled analysis with DIGIMAT. The basic microstructure information is given for the injection mesh and has to be transported to the structural mesh.

With map DIGIMAT offers a comfortable tool for the projection of fiber orientation tensors, initial stresses or temperatures onto the structural mesh. Dependent from the type of data mapping is either applied to elements or nodes. Geometric transformations of meshes such as scaling, translations or rotations can be carried out very easily. Also only a partial mapping of meshes is possible. This isolates the analysis to the regions of interest and therefore significantly reduces the computational effort. Another important point is that injection molded parts can be build into whole assemblies of devices and investigated in their functional environment. The quality of the mapping can be directly controlled in DIGIMAT by using error indicators.

DIGIMAT 4.0 enhances the already existing DIGIMAT technology by the additional module digimat-MX. The Materials Expert (MX) significantly simplifies the way coupled simulations are carried out. Whereas with digimat-MF materials expertise is needed for the setup, with digimat-MX the user does not have to be an expert by himself any longer. He can fully concentrate on the design of his part but still use an advanced simulation technology.

Through its database functionality digimat-MX offers a quick access to coupled simulations. The user simply selects different DIGIMAT materials which have been prepared for him in advance by a materials expert. With DIGIMAT being a common tool among the big materials suppliers the user can directly rely on their know-how. Another possibility is that he uses digimat-MX for the communication with an expert inside his own company or from any other external provider.

The materials expert uses digimat-MX for the automated reverse engineering of DIGIMAT material input data from experimental measurements. The results are stored and distributed via the database functions of MX. This way MX collects all material data of a company in a central point giving the user a quick and easy access to microstructure material models for coupled simulations with DIGIMAT.

The micross module serves for the micromechanical modeling of composite sandwich structures. Being a FEM solver by itself micross enables the investigation of composite panels in standard tests (multi point bending or shear).

The material specifications for the panel are either given directly on the macroscopic level or derived from the microscopic level via homogenization. The easy and intuitive use of this module makes it a standalone tool which can also be applied by people with little experience in setting up FEM calculations.