Efficient Multi-Scale Methods for Short Fiber Reinforced Plastics

In industrial applications, components made of short fiber reinforced polymer composites (SFRP) are often subject to cyclic loads. In a cooperation with Bosch, we developed a multiscale simulation method to provide insight into the viscoelastic and fatigue behaviour of these components.

The elastic and non-linear material properties of injection molded parts strongly depend on the local fiber orientation, which varies continuously within the part: Due to the high length-diameter ratio of the fibers and the large difference between the macroscale of the component and microscale, resolving individual fibers is not possible. To overcome this issue and capture the interaction between the microstructure and macroscopic behavior we used a coupled FEM-FFT two-scale method.

Material Models for the Development of Digital Twins

The fundamental step of this method is to characterize the mechanical behavior on the microscale (see also AIF failure). Together with our project partners from Bosch, we examined the viscoelastic and fatigue behavior of short glass fiber reinforced thermoplastic samples. Our project partners provided mechanical measurements and CT images to analyze the behavior of samples with specific fiber orientations to us. On this basis, we developed suitable material models to produce digital twins of the composite on the microscale of the sample.

A Two-Step Approach Including Full-Field Simulations and Model Order Reductions

We developed a two-step approach to reduce the numerical effort of coupled FEM-FFT multiscale method. In the first step, we used a highly efficient microscale solver, our software tool FeelMath, to perform full-field simulations on representative elementary volumes of the microstructure for sample fiber orientations. Using model order reduction technologies we then obtain effective material models for these fiber orientations and put them them into a database By means of  this database concept we drastically reduce the numerical effort, so that, for the first time, the multiscale method can be applied to industrial problems and thus, can be used profitable by our partner.

Graphic Fibre Orientation Triangle
© Fraunhofer ITWM
Fiber orientation triangle formed by the two largest eigenvalues of the second stage fiber orientation tensor (λ 1, λ 2); (C) isotropic, (M) unidirectional, (Y) planar isotropic fiber orientation.
Electric Window Regulator Drive
© Bosch
Electric window regulator drive with short fibre reinforced plastic housing.
Fluid Injection Molding Simulation
© Fraunhofer ITWM
Local fiber orientation distribution of the window regulator drive housing on the finite element mesh, determined with a FLUID injection molding simulation, shown in the color code of Fig.1.
Multiscale Method
© Fraunhofer ITWM
Local von Mises stress distribution, simulated with the database based multiscale method.