3:30 PM - 3:45 PM
[SVC32-06] "Simplest " experimental model for magma flow : Rheology of dense fibre suspension
Keywords:Magma, Rheology, Suspensions
Despite the extensive efforts of many scientific communities, the understanding of most of the catastrophic natural flows remains still a challenge. Beyond the technical problems related to field measurements, these events present as a result of a combination and coupling of a rich variety of physical phenomena, resulting in highly heterogeneous and complex flows. The main feature of these kinds of flowing materials is their multiphase composition, e.g. : bubbles, solid particles and liquid matrix, which are responsible for their heterogeneous mechanical properties. In particular, magma is composed of elongated solid-brittle crystals suspended in a liquid melted matrix. This geometrical anisotropy could strongly affect the magma capacity to flow. Thus, fibre suspensions could present as the «simplest» model to understand magma flow.
In the present work we present the main problems on magma flow and we will explore from an experimental and analytical approach some available tools in order to understand the rheological behaviour of fibres suspensions. Geometrical features such as aspect ratio, roughness, and fibres concentration could importantly impact on the order-disorder relation and subsequently its capacity to flow; specifically talking: fibres orientation, segregation, shear banding, wall effects, jamming-unjamming transition, etc. The presence of solids particles in suspension increases the anisotropy of the system, leading to non-zero stress difference. As a consequence, additional stresses are carried by the immersed solid fibre in the velocity gradient direction. Thus, the suspended crystals (rigid fibre) in magma will evolve as a frictional-dilatant material, mainly ruled by the shear rate deformation and its resulting granular pressure.
Inspired from granular mechanics, a frictional description presents as an interesting tool to complement classical rheology. Thus, the rheology is described by two dimensionless quantities: the effective friction coefficient (or anisotropy stress ratio) and the resulting global packing fraction.
The mains ideas about jamming transition, rheological properties, orientations and fibres mechanical properties will be discussed, taking into account contact dissipation, lubrication and clustering, with particular emphasis on the discussion about frictional rheology and how these results could gives some interesting clues on the understanding on natural disasters and its limitations.
In the present work we present the main problems on magma flow and we will explore from an experimental and analytical approach some available tools in order to understand the rheological behaviour of fibres suspensions. Geometrical features such as aspect ratio, roughness, and fibres concentration could importantly impact on the order-disorder relation and subsequently its capacity to flow; specifically talking: fibres orientation, segregation, shear banding, wall effects, jamming-unjamming transition, etc. The presence of solids particles in suspension increases the anisotropy of the system, leading to non-zero stress difference. As a consequence, additional stresses are carried by the immersed solid fibre in the velocity gradient direction. Thus, the suspended crystals (rigid fibre) in magma will evolve as a frictional-dilatant material, mainly ruled by the shear rate deformation and its resulting granular pressure.
Inspired from granular mechanics, a frictional description presents as an interesting tool to complement classical rheology. Thus, the rheology is described by two dimensionless quantities: the effective friction coefficient (or anisotropy stress ratio) and the resulting global packing fraction.
The mains ideas about jamming transition, rheological properties, orientations and fibres mechanical properties will be discussed, taking into account contact dissipation, lubrication and clustering, with particular emphasis on the discussion about frictional rheology and how these results could gives some interesting clues on the understanding on natural disasters and its limitations.