Calibration of Fiber Orientation Simulations for LFT—A New Approach

Abstract

Short fiber reinforced thermoplastics (SFT) are extensively used due to their excellent mechanical properties and low processing costs. Long fiber reinforced thermoplastics (LFT) show an even more interesting property profile and are increasingly used for structural parts. However, their processing by injection molding is not as simple as for SFT, and their anisotropic properties resulting from the fiber microstructure (fiber orientation, length, and concentration) pose a challenge with regard to the engineering design process. To reliably predict the structural mechanical properties of fiber reinforced thermoplastics by means of micromechanical models, it is also necessary to reliable predict the fiber microstructure. Therefore, it is crucial to calibrate the underlying prediction models, such as the fiber orientation model, within the process simulation. In general, these models may be adjusted manually, but this is usually ineffective and time-consuming. To overcome this challenge, a new calibration method was developed to automatically calibrate the fiber orientation model parameters of the injection molding simulation by means of optimization methods. This optimization routine is based on experimentally determined fiber orientation distributions and leads to optimized parameters for the fiber orientation prediction model within a few minutes. To better understand the influence of the model parameters, different versions of the fiber orientation model, as well as process and material influences on the resulting fiber orientation distribution, were investigated. Finally, the developed approach to calibrate the fiber orientation model was compared with a classical approach, a direct optimization of the whole process simulation. Thereby, the new optimization approach shows a calculation time reduced by the factor 15 with comparable error variance.

Reorientation of Suspended Ceramic Particles in Robocasted Green Filaments during Drying

“…This procedure assumes that the particle orientation is maintained during drying as strong reorientations during drying would severely hinder such a calibration mechanism. Successful calibrations, however, have been reported for similar systems [ 2 , 66 , 68 ]. As such, the small amount of reorientation during drying that we measured in our work agrees well with these findings.…”

Testing of Mechanical Properties of Polymer PA6 – 30% Glass Fibres

“…This process can cause a local variation of the fibre concentration, which may lead to a change along the flow path of the material as well as through the thickness of the moulded part. A high shear flow gradient in the edge regions leads to the formation of a boundary layer directed parallel to the flow direction, while the fibre orientation in the core region is perpendicular to the global flow direction [7]. Thus, in simplified terms, it can be assumed that injection-moulded thermoplastics reinforced with short fibres can be described by the three-layer model shown in Figure 1.…”

Assessment of Analytical Orientation Prediction Models for Suspensions Containing Fibers and Spheres

“…We find the FT model to greatly predict the orientation in all kinds of different suspensions that originate from the fact that underlying hydrodynamics have such a strong influence on the orientation. With respect to the FT parameter, there is evidence that one fixed parameter is enough, but this parameter, however, should be calibrated once (e.g., by the mechanism by Willems et al [48]), taking care of the exact FT model formulation including the closure approximation.…”