The Dynamics of Rod-like Intruders in Sheared Granular Flow

While there exist many examples of intruding objects within a granular system, the behaviour of a free-flowing intruder is relatively unknown. The purpose of this thesis is to further our understanding of both free-flowing intruder behaviour and its influence on the surrounding grains. We have analysed the dynamics of a single rod-like intruder within a sheared granular flow of disks, for a range of different elongations and sizes, with a focus on its rotational behaviour. This analysis has been undertaken with both experiments and discrete element method simulations. Experiments were performed within the Stadium Shear Device (2D SSD) at the University of Sydney, with modifications made to the 2D SSD in order to apply photoelasticity and infer intergrain contact forces. The rotational behaviour of the elongated intruders resembles that which is seen in systems of entirely elongated particles. Typically, the rod-like intruders orient themselves at some mean angle to the shear direction, with this mean angle always being counter-clockwise. As the intruders elongate, the mean angle approaches the shear flow direction and the intruder is less likely to deviate away from this angle. Using the photoelastic contact force data, we reconstruct the coarse-grained stress field around the intruder. These results suggest that the influence of a single grain-scale free-flowing intruder is likely small. We also analyse the contact forces which are applied to the intruder; it appears that the origin of the mean angle may lie between the balance of contacts which initiate a rotation of the intruder with the contact forces which are created by this rotation. These findings have implications for both the study of free-flowing intruders, e.g. assisting in predicting the final orientation of steel fibres in fibre-reinforced concrete, and for flows of elongated particles; where we have found the orientational behaviour of elongated grains is not a by-product of these grains ordering