Experimental Validation of a Direct Fiber Model for Orientation Prediction

Abstract

Predicting the fiber orientation of reinforced molded components is required to improve their performance and safety. Continuum-based models for fiber orientation are computationally very efficient; however, they lack in a linked theory between fiber attrition, fiber–matrix separation and fiber alignment. This work, therefore, employs a particle level simulation which was used to simulate the fiber orientation evolution within a sliding plate rheometer. In the model, each fiber is accounted for and represented as a chain of linked rigid segments. Fibers experience hydrodynamic forces, elastic forces, and interaction forces. To validate this fundamental modeling approach, injection and compression molded reinforced polypropylene samples were subjected to a simple shear flow using a sliding plate rheometer. Microcomputed tomography was used to measure the orientation tensor up to 60 shear strain units. The fully characterized microstructure at zero shear strain was used to reproduce the initial conditions in the particle level simulation. Fibers were placed in a periodic boundary cell, and an idealized simple shear flow field was applied. The model showed a faster orientation evolution at the start of the shearing process. However, agreement with the steady-state aligned orientation for compression molded samples was found.

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

“…Multiple analytical prediction models exist, two famous ones are the models of Jeffery [16] and Folgar Tucker (FT) [17]. Jeffery's model became famous for its correct orientation prediction within a suspension of arbitrarily shaped particles in all kinds of flow fields and the only limitation of the model is that the concentration must be dilute (i.e., filling fraction φ < (1/a r ) 2 , with aspect ratio a r ) [17] to ensure insignificant particle interactions. The model of Jeffery is given by…”

“…Mechanical properties of fiber-reinforced engineering materials often depend on their local orientation of fibers [1,2]. For example, specimens are reported to be stronger in the direction of fiber alignment [3], or the alignment of the fibers influences the thermal conductivity in sheet layers [4].…”

“…On the one hand, Direct Numerical Simulations (DNS) can be applied on a particle scale, which means that the particles and the flow around them is fully resolved. Methods on this scale mainly differ in the choice whether the momentum of the particle phase is mapped back onto the fluid phase [6,7] (so called two-way coupling (TWC)), or not [2,8] (so called one-way coupling (OWC)), but they all provide the advantage that the orientation of particles can be measured. On this scale, it is also possible to include complex interactions such as surface chemistry [9], magnetism [10], or drying [11].…”

Editorial for the Special Issue on Discontinuous Fiber Composites, Volume II

“…Due to process-induced effects, phenomena like fiber reorientation, attrition and even fiber-matrix phase separation occur. Examples of continued work on changes in fiber microstructure inside a component, presented in this special edition, are shown by the work of Simon et al [1] on direct fiber simulation of orientation development during flow, and the work of Chang et al [2] on the local fiber structure with their investigations into fiber length distribution inside injection molded plaques.…”

“…With increasing computational power in recent years, detailed simulations on particle level with fiber models inside a polymer flow became feasible, thus enabling detailed studies of fiber behavior, regarding orientation, attrition and fiber-matrix phase separation [9,10]. The latest advances with this direct fiber simulation approach are presented in this Special Issue [1,2]. Kech et al present their investigations on the significance of fiber parameter variations for the pARD-RSC orientation model in a shear cell simulation with a similar model [11].…”