Validation of Fiber Breakage in Simple Shear Flow with Direct Fiber Simulation

Tzu-Chuan Chang,Tim Osswald,Angel Yanev,Hakan Celik,Dave Brands,Abrahán Bechara Senior

doi:10.3390/jcs4030134

Abstract

This study aims to use particle level simulation to simulate the breakage behavior of glass fibers subjected to simple shear flow. Each fiber is represented as a chain of rods that experience hydrodynamic, interaction, and elastic effects. In order to validate the approach of the model, the simulation results were compared to simple shear flow experiments conducted in a Couette Rheometer. The excluded volume force constants and critical fiber breakage curvature were tuned in the simulation to gain a better understanding of the system. Relaxation of the fiber clusters and a failure probability theory were introduced into the model to solve the fiber entanglement and thus, better fit the experimental behavior. The model showed agreement with the prediction on fiber length reduction in both number average length and weight average length. In addition, the simulation had a similar trend of breakage distribution compared to a loop test using glass fibers.

Highlights

Discontinuous fiber-reinforced polymers play a significant role in industrial applications due to their lightweight performance and lower manufacturing costs [1,2,3]
During injection molding, fiber breakage already starts in the plasticizing section of the machine and continues as the material is forced through the gate and mold filling
As fiber length is crucial in improving the mechanical performance of a molded product, an increase in fiber length correlates in the increased strength of the product

Summary

Introduction

Discontinuous fiber-reinforced polymers play a significant role in industrial applications due to their lightweight performance and lower manufacturing costs [1,2,3]. It is beneficial to understand the mechanism of fiber breakage during flow, in particular shear flow, which is dominant This will allow the engineer to optimize the process to reduce the length degradation and, gain better mechanical properties. Using the Couette rheometer, Goris et al [9] developed an experimental setup in combination with fiber length measurement to obtain repeatable length degradation of glass fibers at different fiber concentration, initial fiber length, residence time, melt temperature, and processing speed. Some continuum models which are very different from particle level simulations have been developed to obtain the macroscopic picture of breakage by solving the balance equation of fiber length distribution [2,5]. By comparing the model’s predictions to the experimental curve, the influence of adjusting parameters in the model to different conditions is assessed

Direct Fiber Model

Direct Fiber Simulation

Conclusions and Outlook