Obtaining short-fiber orientation model parameters using non-lubricated squeeze flow

As American vehicle fuel efficiency requirements have become more stringent due to the CAFE standards, the auto industry has turned to fiber reinforced polymer composites as replacements for metal parts to reduce weight while simultaneously maintaining established safety standards. Furthermore, these composites may be easily processed using established techniques such as injection molding and compression molding. The mechanical properties of these composites are dependent on, among other variables, the orientation of the fibers within the part. Several models have been proposed to correlate fiber orientation with the kinematics of the polymer matrix during processing, each using various strategies to account for fiber interactions and fiber flexing. However, these all require the use of empirical fitting parameters. Previous work has obtained these parameters by fitting to orientation data at a specific location in an injection-molded part. This ties the parameters to the specific mold design used. Obtaining empirical parameters is not a trivial undertaking and adds significant time to the entire mold design process. Considering that new parameters must be obtained any time some aspect of the part or mold is changed, an alternative technique that obtains model parameters independent of the mold design could be advantageous. This paper continues work looking to obtain empirical parameters from rheological tests. During processing, the fiber–polymer suspension is subjected to a complex flow with both shear and extensional behavior. Rather than use a complex flow, this study seeks to isolate and compare the effects of shear and extension on two orientation models. To this end, simple shear and planar extension are employed, and the evolution of orientation from a planar random initial condition is tracked as a function of strain. Simple shear was imparted using a sliding plate rheometer designed and fabricated in-house. A novel rheometer tool was developed and fabricated in-house to impart planar extension using a lubricated squeeze flow technique, where a low-viscosity Newtonian lubricant is applied to the solid boundaries to minimize the effect of shearing due to the no-slip boundary condition. The Folgar–Tucker model with a strain reduction factor is used as a rigid fiber model and compared against a bead–rod model (a semiflexible model) proposed by Ortman. Both models are capable of predicting the data, with the bead–rod model performing slightly better. Orientation occurs at a much faster rate under startup of planar extension and also attains a much higher degree of flow alignment when compared with startup of steady shear.

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Significance of Model Parameter Variations in the pARD-RSC Model

Journal of Composites Science ◽

10.3390/jcs4030109 ◽

2020 ◽

Vol 4 (3) ◽

pp. 109

Author(s):

Armin Kech ◽

Susanne Kugler ◽

Tim Osswald

Keyword(s):

Fiber Orientation ◽

Short Fiber ◽

Mechanistic Modeling ◽

Model Parameters ◽

Fiber Reinforced ◽

Initial Alignment ◽

Polybutylene Terephthalate ◽

Fiber Volume ◽

Input Parameters ◽

Set Up

This study aims to evaluate how fiber orientation results are dependent on fluctuations in input parameters, such as the average fiber length, fiber volume content, and initial alignment of fibers. The range of parameters is restricted to deviations within one specific short fiber reinforced thermoplastic and is not set up to investigate the differences between materials. The evaluation was conducted by a virtual shear cell based on a mechanistic modeling approach. The fiber orientation prediction model discussed is the pARD-RSC (principal anisotropic rotary diffusion-reduced strain closure) model implemented as a user routine in AUTODESK MOLDFLOW INSIGHT® (AMI®). The material investigated was discontinuous short glass fiber reinforced PBT (polybutylene-terephthalate), which is often used for housings in various industries. It is shown that variation in the input parameters, although having an influence on the fiber orientation model parameters, only affects the final orientation moderately.

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Optimization of Fiber Orientation Model Parameters in the Presence of Flow-Fiber Coupling

Journal of Composites Science ◽

10.3390/jcs2040073 ◽

2018 ◽

Vol 2 (4) ◽

pp. 73 ◽

Cited By ~ 3

Author(s):

Tianyi Li ◽

Jean-François Luyé

Keyword(s):

Fiber Orientation ◽

Coupling Effect ◽

Latin Hypercube Sampling ◽

Fine Tuning ◽

Model Parameters ◽

Fiber Coupling ◽

Molded Part ◽

Orientation Model ◽

Discrepancy Measure ◽

Dependent Viscosity

In this paper, we propose a novel systematic procedure to minimize the discrepancy between the numerically predicted and the experimentally measured fiber orientation results on an injection-molded part. Fiber orientation model parameters are optimized simultaneously using Latin hypercube sampling and kriging-based adaptive surrogate modeling techniques. Via an adequate discrepancy measure, the optimized solution possesses correct skin–shell–core structure and global orientation evolution throughout the considered center-gated disk. Some non-trivial interaction between these parameters and flow-fiber coupling effects as well as their quantitative importance are illustrated. The parametric fine-tuning of orientation models mostly leads to a better agreement in the skin and shell regions, while the coupling effect via a fiber-dependent viscosity improves prediction in the core.

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Macroscopic fiber orientation model evaluation for concentrated short fiber reinforced polymers in comparison to experimental data

Polymer Composites ◽

10.1002/pc.25553 ◽

2020 ◽

Vol 41 (7) ◽

pp. 2542-2556 ◽

Cited By ~ 1

Author(s):

Susanne K. Kugler ◽

Gregory M. Lambert ◽

Camilo Cruz ◽

Armin Kech ◽

Tim A. Osswald ◽

...

Keyword(s):

Experimental Data ◽

Model Evaluation ◽

Fiber Orientation ◽

Short Fiber ◽

Fiber Reinforced Polymers ◽

Fiber Reinforced ◽

Reinforced Polymers ◽

Orientation Model

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Evaluating Rigid and Semi-Flexible Fiber Orientation Evolution Models in Simple Flows

Volume 1: Processing ◽

10.1115/msec2016-8678 ◽

2016 ◽

Author(s):

Gregory M. Lambert ◽

Donald G. Baird

Keyword(s):

Simple Shear ◽

Fiber Orientation ◽

Squeeze Flow ◽

Model Parameters ◽

Mold Design ◽

Random Initial Condition ◽

Complex Flow ◽

Planar Extension ◽

Rod Model ◽

Simple Flows

As American vehicle fuel efficiency requirements have become more stringent due to the CAFE standards, the auto industry has turned to fiber reinforced polymer composites as replacements for metal parts to reduce weight while simultaneously maintaining established safety standards. Furthermore, these composites may be easily processed using established techniques such as injection molding and compression molding. The mechanical properties of these composites are dependent on, among other variables, the orientation of the fibers within the part. Several models have been proposed to correlate fiber orientation with the kinematics of the polymer matrix during processing, each using various strategies to account for fiber interactions and fiber flexing. However, these all require the use of empirical fitting parameters. Previous work has obtained these parameters by fitting to orientation data at a specific location in an injection-molded part. This ties the parameters to the specific mold design used. Obtaining empirical parameters is not a trivial undertaking and adds significant time to the entire mold design process. Considering that new parameters must be obtained any time some aspect of the part or mold is changed, an alternative technique that obtains model parameters independent of the mold design could be advantageous. This paper continues work looking to obtain empirical parameters from rheological tests. During processing, the fiberpolymer suspension is subjected to a complex flow with both shear and extensional behavior. Rather than use a complex flow, this study seeks to isolate and compare the effects of shear and extension on two orientation models. To this end, simple shear and planar extension are employed and the evolution of orientation from a planar random initial condition is tracked as a function of strain. Simple shear was imparted using a sliding plate rheometer designed and fabricated in-house. A novel rheometer tool was developed and fabricated in-house to impart planar extension using a lubricated squeeze flow technique, where a low viscosity Newtonian lubricant is applied to the solid boundaries to minimize the effect of shearing due to the no-slip boundary condition. The Folgar-Tucker model with a strain reduction factor is used as a rigid fiber model and compared against a Bead-Rod model (a semi-flexible model) proposed by Ortman. Both models are capable of predicting the data, with the Bead-Rod model performing slightly better. Orientation occurs at a much faster rate under startup of planar extension, and also attains a much higher degree of flow alignment when compared with startup of steady shear.

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Calibration of Fiber Orientation Simulations for LFT—A New Approach

Journal of Composites Science ◽

10.3390/jcs4040163 ◽

2020 ◽

Vol 4 (4) ◽

pp. 163

Author(s):

Fabian Willems ◽

Philip Reitinger ◽

Christian Bonten

Keyword(s):

Mechanical Properties ◽

Injection Molding ◽

Process Simulation ◽

Fiber Orientation ◽

Model Parameters ◽

Fiber Reinforced ◽

Orientation Model ◽

Fiber Microstructure ◽

Reinforced Thermoplastics ◽

Fiber Reinforced Thermoplastics

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.

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