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

Introduction

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 Technology

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 Marc

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.
This process has been simulated in 3D TIMON. The fibers are randomly oriented in the weldline as visible in the Sample A (area in the dotted line). Sample B shows a diffused orientation in the gate area. The fibers in the area around the weldline and around the diffuse area are quite highly oriented along the sample. This orientation will change progressively from the skin to the core of the sample. In the core the fibers will be randomly oriented.

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.
The results of the DIGIMAT to the Marc analysis show a big difference in the failure pattern between the

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.

Conclusion

Download the article in .pdf

View the magazine in electronic format