Growing length scale near the jamming point in a low-friction, continuously sheared granular system Open Access

Zheng, Jiaqi (2016)

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Granular materials are the second largest amount of material used in industry other than water. One of their interesting properties is that they can change between a flowing state to a rigid state, which is called a jamming transition. In the jammed state many macroscopic observables exhibit critical behavior and a diverging length scale at the jamming point. Many studies of the details of the jamming transition are simulations conducted in a static and frictionless system. Direct experimental evidence of critical behavior is hard to find partially because correlation lengths are difficult to visualize and depend on the system properties. Moreover, in experimental granular studies, friction is very hard to minimize. In order to experimentally study the critical behavior of the jamming transition, we built a low-frictional 2D granular system with a controllable density. By tracking the particles' movement in the system, we observed a growing length scale in the system dynamics. We defined a cluster of spheres which collectively moved like a rigid body. We found that the size of this cluster quickly grows after the system has jammed, and eventually reaches the boundaries of the system.

Table of Contents

Chapter 1: Introduction

1.1 Jamming diagram

1.2 Length scale at jamming for static granular system

1.3 Shearing granular system and its diverging length behavior

1.4 Low friction experiment

1.5 Thesis outline

Chapter 2 Experimental approach

2.1 Outline of experimental setup

2.2 Granular system

2.3 Movable wall with force sensors

2.3.1 Movable wall

2.3.2 Force sensors

2.4 Shearing belt

Chapter 3 Data acquisition

3.1 Force sensors' data

3.1.1 Force data acquisition system

3.1.2 Relaxation of forces in the granular system

3.1.3 Choosing the valid data and adjust threshold

3.2 Image analysis

3.2.1 Determination of the packing fraction

3.2.2 Particle tracking

Chapter 4 Experimental results and analysis

4.1 Results of the force measurement

4.2 Analysis of density in y-direction

4.3 Particles' trajectories

4.4 Displacement distribution

4.5 Decay of velocity away from the shear zone

4.6 Analysis of moving particle clusters

Chapter 5 Conclusion, discussion, and future direction

5.1 Conclusion and discussion

5.2 Future direction

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