A numerical study of extensional flow‐induced crystallization in filament stretching rheometry

Berlo, Frank P. A. van; Cardinaels, Ruth; Peters, Gwm Gerrit; Anderson, Patrick Patrick

doi:10.1002/pcr2.10154

Cited by 4 publications

(8 citation statements)

References 46 publications

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“…However, these models did not account for the two-phase viscoelastic behavior of a semicrystalline polymer melt. Recently, a FEM modeling framework has been established that accounts for the associated transport phenomena (mass, momentum, and energy) along with the nonlinear viscoelastic response and crystallization behavior of isotactic PP in a filament stretching extensional rheometer . The effect of flow on the rheological characteristics and the relaxation spectra prior to the onset of crystallization have been studied.…”

Section: Discussion and Future Outlookmentioning

confidence: 99%

“…Recently, a FEM modeling framework has been established that accounts for the associated transport phenomena (mass, momentum, and energy) along with the nonlinear viscoelastic response and crystallization behavior of isotactic PP in a filament stretching extensional rheometer. 188 The effect of flow on the rheological characteristics and the relaxation spectra prior to the onset of crystallization have been studied. Future work can aim to verify model predictions by studying the processing-property relationships that lead to different morphological and rheological characteristics.…”

Section: J T T T T ( )mentioning

confidence: 99%

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Importance of Polymer Rheology on Material Extrusion Additive Manufacturing: Correlating Process Physics to Print Properties

Das

Gilmer

Biria

et al. 2021

ACS Appl. Polym. Mater.

146

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Recent advances in the field of additive manufacturing (AM) or 3D printing, have garnered serious interest for its potential to substitute time-consuming and costly subtractive and formative manufacturing techniques. Material extrusion (MatEx), employing filament and pelletbased feedstocks, is an AM technique for fabricating three-dimensional objects dictated by a computer-aided design (CAD) file in a layer-by-layer manner. Being inherently a "melt-and-form" technique, the physics of MatEx is strongly dependent on the melt flow behavior of the polymers and hence on their rheology. The focus of this review article is to analyze the current progress in rheological characterizations of filament and pellet-based polymeric feedstocks for application in MatEx. The importance of shear and temperature-dependent viscosities in relation to consistent extrusion through the print nozzle and in the standoff region between nozzle and bed will be highlighted. The importance of shear and/or extensional viscosities and extent of die swell (upon exit from the nozzle) experienced by the polymers under processing parameters relevant to MatEx will be investigated. Postextrusion from the nozzle, the rheological characteristics of the viscous polymer melt as it cools once deposited on the print bed governs the degree of interlayer welding, that impacts the mechanical performance of the printed parts. Controlling and monitoring rheological properties such as zero-shear viscosities and shear moduli of the melt is of significant importance in this region in order to ensure proper mechanical robustness and shape integrity of the deposited layers. Both experimental and theoretical approaches based on polymer chain reptation mechanisms will be reviewed in detail and suggestions to address the existing limitations associated with the process will be provided. Fundamental understanding of the correlation between the classical theories and current understanding based on recent experimentation and analysis is expected to assist the design and development of the next generation of polymer feedstocks and machine designs for MatEx-based AM.

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Section: Discussion and Future Outlookmentioning

confidence: 99%

Section: J T T T T ( )mentioning

confidence: 99%

Importance of Polymer Rheology on Material Extrusion Additive Manufacturing: Correlating Process Physics to Print Properties

Das

Gilmer

Biria

et al. 2021

ACS Appl. Polym. Mater.

146

View full text Add to dashboard Cite

show abstract

“…57 and solved using the stabilized finiteelement method, whose mesh method, mesh movement and projection, time stepping, and stabilization can be found in ref. 58. Boundary conditions of the simulation were no slip on the plate boundaries and surface tension on the free surface of the liquid bridge.…”

Section: Methodsmentioning

confidence: 99%

Torsional fracture of viscoelastic liquid bridges

Chan

Berlo

Faizi

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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Short liquid bridges are stable under the action of surface tension. In applications like electronic packaging, food engineering, and additive manufacturing, this poses challenges to the clean and fast dispensing of viscoelastic fluids. Here, we investigate how viscoelastic liquid bridges can be destabilized by torsion. By combining high-speed imaging and numerical simulation, we show that concave surfaces of liquid bridges can localize shear, in turn localizing normal stresses and making the surface more concave. Such positive feedback creates an indent, which propagates toward the center and leads to breakup of the liquid bridge. The indent formation mechanism closely resembles edge fracture, an often undesired viscoelastic flow instability characterized by the sudden indentation of the fluid’s free surface when the fluid is subjected to shear. By applying torsion, even short, capillary stable liquid bridges can be broken in the order of 1 s. This may lead to the development of dispensing protocols that reduce substrate contamination by the satellite droplets and long capillary tails formed by capillary retraction, which is the current mainstream industrial method for destabilizing viscoelastic liquid bridges.

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“…Below the most relevant details of the numerical procedure are outlined and more details are available in van Berlo et al (2020).…”

Section: Methodsmentioning

confidence: 99%

Towards a universal shear correction factor in filament stretching rheometry

et al. 2021

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Filament stretching rheometry is a prominent experimental method to determine rheological properties in extensional flow whereby the separating plates determine the extension rate. In literature, several correction factors that can compensate for the errors introduced by the shear contribution near the plates have been introduced and validated in the linear viscoelastic regime. In this work, a systematic analysis is conducted to determine if a material-independent correction factor can be found for non-linear viscoelastic polymers. To this end, a finite element model is presented to describe the flow and resulting stresses in the filament stretching rheometer. The model incorporates non-linear viscoelasticity and a radius-based controller for the plate speed is added to mimic the typical extensional flow in filament stretching rheometry. The model is validated by comparing force simulations with analytical solutions. The effects of the end-plates on the extensional flow and resulting force measurements are investigated, and a modification of the shear correction factor is proposed for the non-linear viscoelastic flow regime. This shows good agreement with simulations performed at multiple initial aspect ratios and strain rates and is shown to be valid for a range of polymers with non-linear rheological behaviour.

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A numerical study of extensional flow‐induced crystallization in filament stretching rheometry

Cited by 4 publications

References 46 publications

Importance of Polymer Rheology on Material Extrusion Additive Manufacturing: Correlating Process Physics to Print Properties

Importance of Polymer Rheology on Material Extrusion Additive Manufacturing: Correlating Process Physics to Print Properties

Torsional fracture of viscoelastic liquid bridges

Towards a universal shear correction factor in filament stretching rheometry

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