We have investigated the buckling and snapping unstabilities of beams with a slit, both experimentally and numerically, for different geometries. We find that beams with a slit display non-linear...Show moreWe have investigated the buckling and snapping unstabilities of beams with a slit, both experimentally and numerically, for different geometries. We find that beams with a slit display non-linear symmetry breaking. Specifically they display asymmetric buckled states after symmetrically buckling, a property that can be used in metamaterial design to propagate and amplify symmetry breaking perturbations. We find hysteresis between the "closed" and "open" post-buckling states of the beam and that the transitions between these are snappy. This hysteresis implies that, under compression, these beams are tristable. Exploring two of the states connected by a hysterectic transition, we can regard them as hysterons under a compression field. We find that we can tune the degree of asymmetry as well as the regime where there is hysteresis by modifying the geometrical parameters of the beam. Both the non-linear symmetry breaking and its characteristic as hysterons make beams with a slit useful tools to achieve functionality in metamaterial design.Show less
In this thesis we will demonstrates how to construct a counting mechanical metamate- rial that is based on bi-stable buckling beams by creating a material that can count to ten. By coupling...Show moreIn this thesis we will demonstrates how to construct a counting mechanical metamate- rial that is based on bi-stable buckling beams by creating a material that can count to ten. By coupling bistable buckling beams in a suitable geometry we can design mate- rials that when cyclically compressed between two critical strains. We show that when two adjacent buckled beams touch, there is a characteristic length scale - the inversion length - that determines which of two beams snaps through when compressed to the snapping strain. We experimentally and analytically work out the characteristic inver- sion distance length scale that determines the outcome of the battle of the buckling beams and show how to modify beam geometries to design counting behaviour for many beam materials.Show less
The DNA in eukaryotic organisms is largely stored in a compact wrap around histone proteins to form nucleosomes. The mechanics of the DNA play a major role in the biological processes for which the...Show moreThe DNA in eukaryotic organisms is largely stored in a compact wrap around histone proteins to form nucleosomes. The mechanics of the DNA play a major role in the biological processes for which the DNA is used. In this thesis we will computationally show that we can study the mechanics of the DNA with a simplified computational model. By parametrically constraining the DNA around a superhelical curve we can calculate the mechanical energy of the DNA by only the sequence of the DNA and the positions along the curve. We will demonstrate how, with Monte Carlo methods we can effectively estimate the sequence and position statistics of nucleosomal DNA.Show less
In this research we aim to design metamaterials that can perform elementary logic operations. In order to do this, we describe the folding relations of Euclidean and non-Euclidean four-vertex...Show moreIn this research we aim to design metamaterials that can perform elementary logic operations. In order to do this, we describe the folding relations of Euclidean and non-Euclidean four-vertex origami. Moreover, we combine folding relations by combining two four-vertices into a two-vertex composite. We characterize the behavior of these vertices and composites and unravel the extensive design space. Our final goal is to choose a region of the design space for which the vertex simulates an inverter; a logic gate which inverts a signal. We find that a single four-vertex can come close to performing the preferred inverter behavior, but never fully reaches our goals. However, using a second four-vertex leading to a two-vertex composite can meet the criteria of an inverter. Our work opens new possibilities for the rational design of functional materials.Show less
We look at a mechanical metamaterial whose stiffness does not scale inversely proportional to its length. We perform tensile tests to study the relation between the length and the stiffness of the...Show moreWe look at a mechanical metamaterial whose stiffness does not scale inversely proportional to its length. We perform tensile tests to study the relation between the length and the stiffness of the metamaterial. We find two regimes for the stiffness, which are separated by a characteristic length. We explain the cause of this length and show that we can alter its value. Lastly we set up a model that simulates the behavior of the metamaterial in tension and can reproduce the experimental data.Show less
This work explores the design, synthesis and actuation of temperature sensitive hydrogel-elastomer bilayers. Following previous research we created a protocol to graft poly-N-isopropylacrylamide ...Show moreThis work explores the design, synthesis and actuation of temperature sensitive hydrogel-elastomer bilayers. Following previous research we created a protocol to graft poly-N-isopropylacrylamide (PNIPAM) on top of a rubber substrate. These bilayers can be bent by changing the temperature of the system using a heat bath. Novel bilayers are designed where a mechanical instability is introduced. None of the designed instabilities are triggered during actuation, instead the bilayers bend in a different direction.Show less
In this thesis we investigate the effects of bending on a Miura Ori Origami sheet. In particular we are going to analyse a simplified version, a single stripe made by a row of unit cells. We will...Show moreIn this thesis we investigate the effects of bending on a Miura Ori Origami sheet. In particular we are going to analyse a simplified version, a single stripe made by a row of unit cells. We will investigate how the bending stiffness and the curvature at the surface are changing with the variation of the fold angle of the structure and with the application of an external force. We investigate the curvature by scanning the samples with a 3D scanner and then analysing the data. To probe the bending stiffness, we use an Instron, a uniaxial compression device.Show less
To evaluate if the multistable behaviour of corrugated plastic sheets under low tensile strain is a purely elastic phenomenon, tensile strain experiments were performed on thin silicone rubber...Show moreTo evaluate if the multistable behaviour of corrugated plastic sheets under low tensile strain is a purely elastic phenomenon, tensile strain experiments were performed on thin silicone rubber sheets with corrugations. To perform such experiments, thin silicone rubber sheets with and without corrugations were cast by using a voltage controlled spin-coater. For the characterization of the sheets, a micrometer was used to measure the thickness in order to obtain values for the average thickness and homogeneity of the sheets. A protocol for tensilse tests on smooth thin silicone rubber sheets by using an Instron tensile test machine was formulated to obtain a value for the Young’s Modulus of the used silicone rubber experimentally. A series of low tensile strain experiments was carried out on a set of thin silicone rubber sheets with different kinds of corrugation patterns, after which the behaviour of these sheets was compared to the behaviour of corrugated plastic sheets under the same tensile strain.Show less
When drops of water are sprayed onto a hot pan, they will hover above the surface on a layer of their own vapor, rather than boiling away quickly. This is the Leidenfrost effect, which has been...Show moreWhen drops of water are sprayed onto a hot pan, they will hover above the surface on a layer of their own vapor, rather than boiling away quickly. This is the Leidenfrost effect, which has been observed with both liquids and stiff solids. Here we present a new variation of the Leidenfrost effect using soft solids. By dropping hydrogel spheres onto hot surfaces we find that, rather than gently levitating above the surface, they exhibit sustained bouncing motion, and squeak on each contact. The sustained bouncing implies that the spheres gain kinetic energy during each impact. We investigate the temperature dependence of this effect, finding a minimum required temperature like in the ordinary Leidenfrost effect. We also explore the effect of salt in the growing solution and of the sphere’s temperature. Finally we use a high-speed camera to uncover the mechanism of this effect, finding that the sphere exhibits high-frequency microscopic oscillations at the gel-substrate interface, which generate the sound heard on each bounce and inject the kinetic energy required to sustain the bouncing.Show less
In this thesis, we probe the bending stiffness of origami metamaterials, to investigate under which conditions origami can be described as continuum media. The Miura Ori pattern was bent using two...Show moreIn this thesis, we probe the bending stiffness of origami metamaterials, to investigate under which conditions origami can be described as continuum media. The Miura Ori pattern was bent using two mechanical tests: three point bending test and cantilever bending. Our origami metamaterials at rest can be characterised by the opening angle between adjacent plates, which specifies how much the structure is folded. We varied two things, the width and the opening angle. The bending stiffness of the Miura Ori sheet at different widths showed significant deviations from continuum classical elastic theory. These deviations differed in behaviour and this was dependant on the opening angle of the sheet. When the Miura Ori sheets were almost flat folded, an continuum mechanical behaviour was seen when the width was small. The deviations were seen when the width increased. When the sheets were opened, possible finite size effects were determined that corresponded to Cosserat elasticity. Tests showed that the bending stiffness increased with the opening angle. This contradicts previously made theoretical predictions.Show less
In recent years, a number of artificial materials (so called metamaterials) have been developed, tailoring exotic responses to mechanical stress by exploiting geometrical features. A particular...Show moreIn recent years, a number of artificial materials (so called metamaterials) have been developed, tailoring exotic responses to mechanical stress by exploiting geometrical features. A particular class of 2D metamaterials consists of tilings of polygons that can fold onto themselves by exploiting a mechanical instability triggered by compression. A subclass of these materials shows a sequence of two ordered states (one partially and one fully closed) when biaxially compressed; however, the reason why such networks fold in multiple steps is yet elusive and we are unaware of a general rule to design them; it is even unknown whether it is possible to increase the number of ordered states sequentially reached by a network during the folding process. In order to answer these questions, first we investigate a variety of designs to determine the role played by symmetries, topology and elastic energy; secondly, we focus on a hierarchical approach to design a network with three folding stages; finally, we fully characterize the mechanical response of this new network and we study how the order of the system evolves during the folding process.Show less
We report the design and construction of a mechanism, consisting of rigid plates and freely hinging connectors, that is used to describe and study the motions of a mechanical metamaterial called...Show moreWe report the design and construction of a mechanism, consisting of rigid plates and freely hinging connectors, that is used to describe and study the motions of a mechanical metamaterial called the ‘metacube’. For this design, a novel method is used, where the mechanism is 3D printed and the accuracy is mechanically tested. We present an accurate mechanism that describes the motions of the metacube. This mechanism can be used to not only gain further understanding of the properties of the metacube, but also shows previously undiscovered properties of this mechanical metamaterial.Show less
