Ifsttar PhD subject

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Title : Flow mechanisms and shape of deposits in 3D printing of concrete

Main host Laboratory - Referent Advisor   -

Director of the main host Laboratory   -

PhD Speciality Mécanique des fluides

Axis of the performance contract 2 - COP2017 - More efficient and resilient infrastructure

Main location Marne-la-Vallée

Doctoral affiliation UNIVERSITE DE MARNE-LA-VALLEE

PhD school SCIENCES, INGENIERIE ET ENVIRONNEMENT (SIE)

Planned PhD supervisor COUSSOT Philippe  -  Université Gustave Eiffel  -  Navier

Planned financing Contrat doctoral  - Ifsttar

Abstract

In the construction field, 3D concrete printing can be used to build structures that have complex shapes, without formwork and with a smaller amount of material than conventional methods. To do so, the usual technique consists to extrude then deposit a concrete filament on the previous layer. During the deposition step, some instabilities may appear, inducing some weaknesses in the 3D structure.
We studied instabilities of linear deposits with a setup developed inside the laboratory that allows for an independant 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. Their behaviour was well characterized and was considered as model for the concrete. The printing parameters were changed – exit speed, translation speed, height, nozzle diameter and yield stress – and observed various deposition patterns : discontinuous line, straight line, meanders, alternated coils and translated coils. We then demonstrated in a semi-empirical way that two non-dimensional parameters fully describe the conditions of appearance of the patterns: V* the ratio of translation speed over exit speed, and H* the ratio of height over nozzle diameter. We concluded with theoretical explanations for the transition between patterns, which completed our understanding of the impact of the printing parameters on the shapes and instabilities of deposits
We also developed some image analysis 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 wheighing a detached drop of filament.
This work provides an understanding on how a filament deposits itself in 3D printing for the construction. 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.

Keywords : 3D printing,rheology,elongation,cement,clay

Main host Laboratory - Referent Advisor	-
Director of the main host Laboratory	-
PhD Speciality	Mécanique des fluides
Axis of the performance contract	2 - COP2017 - More efficient and resilient infrastructure
Main location	Marne-la-Vallée
Doctoral affiliation	UNIVERSITE DE MARNE-LA-VALLEE
PhD school	SCIENCES, INGENIERIE ET ENVIRONNEMENT (SIE)
Planned PhD supervisor	COUSSOT Philippe - Université Gustave Eiffel - Navier
Planned financing	Contrat doctoral - Ifsttar
Abstract In the construction field, 3D concrete printing can be used to build structures that have complex shapes, without formwork and with a smaller amount of material than conventional methods. To do so, the usual technique consists to extrude then deposit a concrete filament on the previous layer. During the deposition step, some instabilities may appear, inducing some weaknesses in the 3D structure. We studied instabilities of linear deposits with a setup developed inside the laboratory that allows for an independant 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. Their behaviour was well characterized and was considered as model for the concrete. The printing parameters were changed – exit speed, translation speed, height, nozzle diameter and yield stress – and observed various deposition patterns : discontinuous line, straight line, meanders, alternated coils and translated coils. We then demonstrated in a semi-empirical way that two non-dimensional parameters fully describe the conditions of appearance of the patterns: V* the ratio of translation speed over exit speed, and H* the ratio of height over nozzle diameter. We concluded with theoretical explanations for the transition between patterns, which completed our understanding of the impact of the printing parameters on the shapes and instabilities of deposits We also developed some image analysis 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 wheighing a detached drop of filament. This work provides an understanding on how a filament deposits itself in 3D printing for the construction. 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.
Keywords :	3D printing,rheology,elongation,cement,clay

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