Paper Number
TM21
Session
Rheometry: Advanced Techniques and Methods
Title
Measurements of yield stress materials using 3D printed fractal vanes
Presentation Date and Time
October 22, 2019 (Tuesday) 1:55
Track / Room
Track 1 / Room 305A
Authors
- Owens, Crystal E. (Massachusetts Institute of Technology)
- Hart, Anastasios J. (Massachusetts Institute of Technology)
- McKinley, Gareth H. (Massachusetts Institute of Technology, Department of Mechanical Engineering)
Author and Affiliation Lines
Crystal E. Owens, Anastasios J. Hart, and Gareth H. McKinley
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA
Speaker / Presenter
Owens, Crystal E.
Text of Abstract
We design and print a family of novel vane tools that combines desirable features of the standard 4-arm vane and cylindrical bob into a hybrid fractal structure. These vanes, produced by stereolithographic (SLA) 3D printing, has a more axisymmetric stress distribution than the 4-arm vane, less material damage/displacement upon sample loading than the bob, and help eliminate wall slip. Meanwhile, SLA permits creation of intricate structures with resolution <200µm on tooling >5 cm in size, with print-to-print repeatability <30µm, from materials having wide chemical compatibility and good mechanical stability. We discuss principles for design optimization for a given sample in terms of displaced material volume and stress homogeneity, showing fractal designs by tuning the number of vane arms. We add a 3D printable self-centering cup with ribbed inner surface (and solvent trap) to complete the vane-in-cup geometry.
Furthermore we develop and validate a torque-to-stress conversion equation for fractal vanes with 4-24 arms. Applying this equation to several printed vanes, we show that we can measure the viscosity of Newtonian silicone oils (10-1000mPa.s) within 8% of reference values from cone-and-plate tests. We also measure the stress-strain rate flow curve of a simple yield stress fluid (Carbopol) within 5% (or within 0.2% for a 24-arm fractal vane), showing that these fractal designs are useful, not just made in vain. Finally, we use the optimal fractal vane for measuring transient stress growth measurements on a series of complex thixo-elasto-viscoplastic materials including a jammed emulsion (mayonnaise), an alkaline battery slurry (pH=12), and a multicomponent fibrous dispersion (tomato ketchup).