Errors are everywhere, and mechanical failures are especially common: buckled grain silos and cracked support columns are, justly, seen as an issue to be avoided. But flaws can also be used to... Show moreErrors are everywhere, and mechanical failures are especially common: buckled grain silos and cracked support columns are, justly, seen as an issue to be avoided. But flaws can also be used to design materials with unique functionalities. In the work presented here, we use two types of imperfections to create functional structures. First, we design materials that are locally stiff or soft, depending on how they are actuated, using topological imperfections: mistakes in their underlying architecture. Second, we create structures that shape-morph, because their individual elements fail, buckle, and snap- features that should be avoided otherwise. Show less
This thesis explores how rheology and statistical mechanics can be used to describe driven granular materials. Chapter 1 is an overview of the current knowledge of slow granular flows. In Chapter 2... Show moreThis thesis explores how rheology and statistical mechanics can be used to describe driven granular materials. Chapter 1 is an overview of the current knowledge of slow granular flows. In Chapter 2 we characterize the liquid-like behaviour of a granular system excited by flow in a split-bottom geometry. In Chapter 3 we describe the fluctuations experienced by an object floating in our granular liquid and compare these fluctuations to the Brownian motion of particles in a thermal system. In Chapter 4 we characterize the motion of objects moving in a granular system excited by oscillatory flow. Finally, in Chapter 5, we describe both the microscopic and macroscopic motion of pucks on an air hockey table. We find the the system exhibits equipartition of rotational and translational energy and that the system can be described by van der Waals' equation of state. Show less
This thesis is about weakly driven granular flows and suspensions. Chapter 1 is an overview of the current knowledge of slow granular flows in so-called split-bottom geometries, which in essence... Show moreThis thesis is about weakly driven granular flows and suspensions. Chapter 1 is an overview of the current knowledge of slow granular flows in so-called split-bottom geometries, which in essence consist of a disk rotating at the bottom of a container. In chapter 2 we study dry granular flows in this split-bottom geometry, both in the frictional, slow, rate-independent regime, and in the liquid-like, rate dependent regime which is reached for faster flows. Chapters 3-5 deal with the flow of suspensions in the same geometry. We improve the so-called index matched scanning technique, that allows 3D imaging of the suspensions. Also for the suspension we study both the slow, rate independent and the faster, rate dependent regime. In all cases we combine 2D and 3D imaging of the flow with rheological measurements. Chapter 6 is devoted to the rheology of dry, weakly vibrated granular media. In chapter 7 we revisit a classic experiment on the compaction of granular media. Show less
We study the shear flow of two-dimensional foams, i.e., a monolayer of bubbles floating on a soapy solution. We successfully connect local and global flow behaviour
