Micro/Bio/Nanofluidics (Shen) Unit would like to invite you to the virtual seminar by Dr. Anatole Geffrault on April 25 (Tuesday).
 
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Date: April 25, 2023
Time: 3:00-3:30PM
**Zoom session
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*Zoom information

https://oist.zoom.us/j/93935538689?pwd=ZVBYYTJlUUdiTW9ZOEE3ZTY5MkJwQT09

Meeting ID: 939 3553 8689
Passcode: 833305

Speaker:

Anatole Geffrault
PhD
Fluid mechanics, Navier lab, Gustave Eiffel University

Title:

Shape of deposits and flow mechanisms in 3D printing of yield stress fluids

Abstract:

3D printing of yield stress fluids (i.e., materials able to flow like liquids only beyond a critical stress) is opening new doors in the fields of construction, food or medicine. The usual printing technique consists to extrude and then deposit a filament of yield stress fluid onto the previous layer. One major difficulty is that, during the deposition process, some instabilities may appear and have a catastrophic impact on the final 3D structure

We studied instabilities of linear deposits with a setup developed inside the laboratory that allows for an independent control of the exit speed of the filament and the translation speed of the nozzle. These controlled experiments were carried out on various simple yield stress fluids and on a cement. The printing parameters were changed – exit speed, translation speed, height, nozzle diameter and yield stress – and we observed various deposition patterns : discontinuous line, straight line, meanders, alternated coils and translated coils. Then, we demonstrate that the transitions (frontier curves) between pattern regions can be predicted by theoretical arguments.

We also developed image analyses that allowed us for a detailed study of the break-up of a filament of yield stress fluid due to gravity. We demonstrated that the analysis of the break-up makes it possible to perform elongational rheometry. From that, we obtained elongational flow curves of simple yield stress fluids and we proposed a simple test to measure a yield stress by weighing a detached drop of filament.

This work provides an understanding on how a filament deposits itself in 3D printing by extrusion. It could be used to avoid the appearance of instabilities in the deposition process, but also to think of new printing strategies that would use the patterns.

Host:

Prof. Amy Shen