5:15 PM - 6:45 PM
[O07-P05] Rotary shear experiments using particles floated on heavy liquid: Toward modeling the brittle-ductile transition
★Invited Papers
Keywords:Analogue experiment, Fault, Earthquake, Particle dispersed system, Particle raft
To investigate the deformation mechanism of fault gouges or sediments, we performed rotational shear experiments on spherical gel particles floated on a liquid surface. Due to floating particles, bottom friction becomes zero, and due to rotational geometry, steady state can be reached. By varying the particle packing fraction, both viscous flow and stick-slip behaviors can be occurred. We can also investigate the brittle-ductile transition between them. By taking in-situ photography during the deformation experiments, we can track each particle motion, allowing us to connect the temporal evolution of particle arrangement to macroscopic mechanical properties.
As an experimental material, we use spherical particles made of soft gel having enhanced elasticity and plasticity. The particles were white, opaque, and approximately 4 mm in diameter. We use biobeads for filtration of water as the sample particles, while water gel jelly beads can be an alternative, and you can get either material for about 1000 yen per 100 g. As the liquid on which the particles can float, we use sodium polytungstate solution, which is used for heavy-liquid separation of minerals. The density (specific gravity) of aqueous solution of sodium polytungstate can be increased up to 3.1 or more depending on the concentration; moreover, it is transparent to film the particles in-situ, and less toxic to easily handle [1]. Sodium polytungstate solution can also float glass beads which are commonly used in experiments on jamming particles (e.g., [2]), allowing us to compare the results of gel balls to previous studies using glass beads.
The gel particles are floated on the heavy liquid in a transparent beaker. The thickness of the particle layer was limited to a single particle. Rotational shearing is applied by inserting a cylinder perpendicular to the particle layer and rotating it. The rotating cylinder is connected to a motor by a spiral spring which measures torque. During deformation experiments, we also take in-situ images from the bottom of the beaker to analyze time series images of the particle layer.
Experiments were performed under two different boundary conditions: whether the same particles as the sample were glued to the side wall of the rotating cylinder or not. When the particles were glued, stick-slip corresponding to particle interlocking and faulting, occurred regardless of the number of particles in the particle layer. The recurrence interval of stick-slip and the amount of stress drop increased as the number of particles increased. Image analysis revealed that the width and shape of the shear zone varied depending on the number of particles. On the other hand, when the particles were not glued to the cylinder, we observed a gradual transition from creep to stick-slip as the number of particles increased, like the brittle-ductile transition.
Particle dispersed system consisting of many particles like this study exhibits jamming transition, discontinuous mechanical transition corresponding to freezing of particle arrays when the particle packing fraction exceeds a threshold value [3]. By phenomenologically reproducing the viscous-frictional transition associated with the jamming transition, we can investigate the shear properties of unconsolidated materials such as fault fracture zones and landslide slip planes. In addition, defects can be reproduced in colloidal crystals, one of the particle dispersed systems, like lattice defects of mineral crystals [4]. Therefore, the jamming transition experiments might help us to discuss the brittle-ductile transition mechanism of tectonic plate composed of polycrystalline minerals.
[1] Danhara et al. (1992) The use of sodium polytungstate, a new nontoxic heavy liquid. Chishitsu News.
[2] Higashi & Sumita (2009) Experiments on granular rheology: Effects of particle size and fluid viscosity. JGR.
[3] Liu & Nagel (1998) Jamming is not just cool any more. Nature.
[4] Schall et al. (2004) Visualization of Dislocation Dynamics in Colloidal Crystals. Science.
As an experimental material, we use spherical particles made of soft gel having enhanced elasticity and plasticity. The particles were white, opaque, and approximately 4 mm in diameter. We use biobeads for filtration of water as the sample particles, while water gel jelly beads can be an alternative, and you can get either material for about 1000 yen per 100 g. As the liquid on which the particles can float, we use sodium polytungstate solution, which is used for heavy-liquid separation of minerals. The density (specific gravity) of aqueous solution of sodium polytungstate can be increased up to 3.1 or more depending on the concentration; moreover, it is transparent to film the particles in-situ, and less toxic to easily handle [1]. Sodium polytungstate solution can also float glass beads which are commonly used in experiments on jamming particles (e.g., [2]), allowing us to compare the results of gel balls to previous studies using glass beads.
The gel particles are floated on the heavy liquid in a transparent beaker. The thickness of the particle layer was limited to a single particle. Rotational shearing is applied by inserting a cylinder perpendicular to the particle layer and rotating it. The rotating cylinder is connected to a motor by a spiral spring which measures torque. During deformation experiments, we also take in-situ images from the bottom of the beaker to analyze time series images of the particle layer.
Experiments were performed under two different boundary conditions: whether the same particles as the sample were glued to the side wall of the rotating cylinder or not. When the particles were glued, stick-slip corresponding to particle interlocking and faulting, occurred regardless of the number of particles in the particle layer. The recurrence interval of stick-slip and the amount of stress drop increased as the number of particles increased. Image analysis revealed that the width and shape of the shear zone varied depending on the number of particles. On the other hand, when the particles were not glued to the cylinder, we observed a gradual transition from creep to stick-slip as the number of particles increased, like the brittle-ductile transition.
Particle dispersed system consisting of many particles like this study exhibits jamming transition, discontinuous mechanical transition corresponding to freezing of particle arrays when the particle packing fraction exceeds a threshold value [3]. By phenomenologically reproducing the viscous-frictional transition associated with the jamming transition, we can investigate the shear properties of unconsolidated materials such as fault fracture zones and landslide slip planes. In addition, defects can be reproduced in colloidal crystals, one of the particle dispersed systems, like lattice defects of mineral crystals [4]. Therefore, the jamming transition experiments might help us to discuss the brittle-ductile transition mechanism of tectonic plate composed of polycrystalline minerals.
[1] Danhara et al. (1992) The use of sodium polytungstate, a new nontoxic heavy liquid. Chishitsu News.
[2] Higashi & Sumita (2009) Experiments on granular rheology: Effects of particle size and fluid viscosity. JGR.
[3] Liu & Nagel (1998) Jamming is not just cool any more. Nature.
[4] Schall et al. (2004) Visualization of Dislocation Dynamics in Colloidal Crystals. Science.