| [February 17, 2012]|
Leading the Way in Composites; Paving the way with the most advanced material modeling technology
e-Xstream engineering is an MSC Software Community Partner who offers DIGIMAT, the unique nonlinear multi-scale material and structure modeling platform that addresses composite material suppliers and end user’s needs. DIGIMAT enables the design of innovative and optimal materials and structures while reducing the related development time and costs needed to manufacture them.
The DIGIMAT to Marc solution bridges the gap between the composite microstructure, as induced by the manufacturing process, and the end- performance of the composite structure
IntroductionEnvironmental issues have been a key topic within R&D strategies for the main technological industries (e.g. aeronautic and automotive industries) for more than 10 years. These industries must find a new solution to meet the demands of increasingly stringent environmental norms while also reducing the development cost and the time to the market for their product. Switching to composite materials, which provide the greatest performance properties compared to density, are the most interesting solution to consider tackling these new challenges. These materials provide outstanding properties in mechanical, thermal and electrical fields. The word composite is a generic term where different types of composites can be distinguished: unidirectional composite, short fiber reinforced plastic, nano composite, ceramics.
Introducing composite material in part that was traditionally made of metals is a new challenge for engineers. Composite materials exhibit nonlinear anisotropic material properties that are much more complex to model than the properties of good old steel. The question arising is then how to accurately model the complex behavior of a composite material in an industrial part?
DIGIMAT TechnologyWith that target in mind, e-Xstream engineering has developed the DIGIMAT software suite. DIGIMAT provides the most advanced material modeling technology using a micromechanical multi-scale approach to account for the nonlinear, anisotropic, strain rate- and temperature- dependent behavior of composite materials. It is best suited to handle material modeling in the frame of global simulation processes in order to improve the accuracy of FEA. Material modeling would be incomplete if it did not to include failure modeling. This is a great challenge for part producers, especially in the field of composite materials. DIGIMAT perfectly addresses such a challenge. Accurate material computation with DIGIMAT can be performed on a Representative Volume Element (RVE) by the means of Digimat-MF. This is a
way to study the material itself and the microstructure that constitutes it. It can also be done in the frame of FEA on structural parts by the means of DIGIMAT interfaces to CAE codes. DIGIMAT is interfaced with the most important FE codes available on the market, both implicit as well as explicit, and Marc is an important part of this. In the case of FEA, the DIGIMAT material computation is performed at each integration point of the FE mesh. This is done at every time step such that the continuously evolving material state is dynamically updated during the analysis.
DIGIMAT Coupling to MarcDIGIMAT’s interface to Marc has been used by the Kanazawa Institute of technology and UES Software Asia, Inc. to evaluate the effect of a weldline on the failure of a hexahedral beam during a bending test. The beam is made of PP reinforced by short glass fibers (PPGF). The specific mold has been designed to create in one injection process two beams: one with a weldline (SampleA) and one without (Sample B). Figure 1 shows a sketch of this mold. This process has been simulated in 3D TIMON (Toray Engineering). The fibers are randomly oriented in the weldline as visible in the Sample A. DIGIMAT is used to model the elasto-plastic behavior of the PPGF material. The inputs for DIGIMAT material model
are the mechanical properties of the polypropylene material and glass fiber. The microstructure must be also described by the mass fraction of fiber, their aspect ratio and the fiber orientation tensors.
DIGIMAT is used to model the elasto- plastic behavior of the PPGF material. The inputs for DIGIMAT material model are the mechanical properties of the polypropylene material and glass fiber. The microstructure must be also described by the mass fraction of fiber, their aspect ratio and the fiber orientation tensors. Figure 3 illustrates the effect of the fiber orientation on the composite behavior. The composite is much stiffer when the fibers are aligned with the tensile direction than with a random fiber orientation. The local nonlinear anisotropic behavior of the composite material in the beam is captured by using the DIGIMAT Micro method. In this method, DIGIMAT is strongly coupled with Marc. In every integration point of the beam, DIGIMAT is called by Marc to predict the behavior of the composite as function of the fiber orientation observed in this point. This procedure is repeated in every integration point of the beam and for all time increment. To predict the failure pattern of the beam, the First Pseudo Grain Failure (FPGF) model is used. FPGF is the only known failure model specifically dedicated to model failure of short fiber-reinforced plastics. The FPGF model offers the great advantage of enabling to use the mere maximum stress limits of the composite which are most easy to measure experimentally.
Sample A and Sample B (see Figure 4). This difference can be captured because DIGIMAT is predicting the right material behavior in every point of the part by taking into account the local microstructure of the material. In Sample A, the failure line is concentrated around the weldline. The strength of the composite is lower in this area due to the random orientation of the fibers. In Sample B, the failure pattern is not a line anymore but an area. This is due to the diffused orientation of the fibers in the center of the beam. This diffused orientation is due to the specific polymer flow at the gate of the mold.
ConclusionDIGIMAT is a unique software platform for the nonlinear multi- scale modeling of a large variety of materials. The DIGIMAT to Marc solution bridges the gap between the composite microstructure, as induced by the manufacturing process, and the end-performance of the composite structure. In this study, DIGIMAT to Marc has been able to accurately capture the local nonlinear anisotropic behavior of composite material and the effect on the failure pattern. DIGIMAT is the standard solution used across many industries to model the behavior of composites as a function of their underlying microstructure.