Posters

Information

Posters will be presented in the multi-purpose room of Northwest building. The poster board dimensions are 35'' wide and 47'' tall.

Participants

P1: Sina Askarinejad - Worcester Polytechnic Institute

In order to provide the outstanding mechanical functions, nature has evolved complex and effective functionally graded interfaces. Particularly in nacre, aragonite-protein interface in which the proteins behave stiffer and stronger in proximity of aragonite minerals provide an impressive role in structural integrity and mechanical deformation of the natural composite. However, further research on the toughening mechanisms and the role of the interface properties as a guide on design and synthesize new materials is essential.

P2: Nakul Bende - UMass Amherst

"Material systems and mechanics for shape-programming of polymer sheets and shells"

Soft 'active' matter have been a recent interest, inspired by numerous biological systems. Through a fundamental understanding in relationship between material, mechanics and geometry we propose robust pathways to program on-demand shape transitions in polymer sheets and shells by leveraging both mechanics and responsive polymer materials.

P3: Chao Chen - Harvard University

"Flaw sensitivity of highly stretchable materials"

The stretchability of stretchable materials is insensitive to small cuts, but reduces markedly when the cuts are large. We show that this transition occurs when the depth of cut exceeds a material-specific length, the length of flaw sensitivity, defined by the ratio of the fracture energy measured in the large-cut limit and the work to rupture measured in the small-cut limit. The length of flaw sensitivity is applicable to all materials, from nanometers for brittle materials to centimeters for tough materials.

P4: Weilin Deng - Brown University

"Depth-Dependent Hysteresis in Adhesive Elastic Contacts"

We perform atomistic simulations of adhesive contact and show that the roughness alone coupled with adhesion can give rise to depth-dependent hysteresis (DDH) at the atomistic scale. Through simulations, we demonstrate that the mechanism of DDH is resulted from the cumulative effect of a series of jump instabilities during the load-unload cycle, which are due to the unstable contact growth and recession across the surface imperfections.

P5: Ehsan Hajiesmaili - Harvard University

"Modelling of dielectric elastomers with wire network electrodes"

This presentation discusses the modelling of dielectric elastomer membranes with percolating network of wires as their electrode. The model consists of a dielectric elastomer membrane coated by a compliant electrode on one side and a wire touching the other side. Applying a voltage between the wire and the compliant electrode causes an attraction force between them and therefore deforms the membrane.
Finite elements method is implemented to simulate the actuation of the membrane under an applied voltage. Simulation of dielectric elastomer actuators usually involves electromechanical analysis of only one dielectric elastomer membrane coated with compliant electrodes on both surfaces. However, the modelling discussed in this presentation requires multi-physics contact between the wires and the elastomer surface and on top of that the free space surrounding the wire needs to be modelled for which there’s no mechanical equation, and no meaning for its deformation.
First, the electrostatic and mechanical formulations are discretized and expressed in finite elements form. Then, the finite element formulation is implemented in ABAQUS UEL. Finally, we discuss about the challenging part of this modelling, i.e. the free space effect and the multi-physics contact between the wire and elastomer.

P6: Nan Hu - Dartmouth College

"Kirigami-based Piezoelectric Materials for New Functional Devices"

We introduce kirigami (a type of origami with cuts) patterns on PVDF thin film. By investigating their responses under axial stretching, we found that the kirigami-based PVDF films can have larger stretchablility (i.e. extend strain range) without significantly losing their voltage output. Hybrid cutting pattern was designed and studied structure to improve the strain range and voltage output. Preliminary results showed that kirigami-based PVDF thin films can even have a larger voltage output than the one without cutting, which could enable application in energy harvesting and smart sensing.

P7: Srivatsan Hulikal - Brown University

"Experimental calibration of Cahn-Hilliard model for LiSn electrodes"

In the talk/poster, I will show how the standard Cahn-Hilliard equations commonly used in modeling phase transforming electrodes for Li-ion batteries implies the interface is always in local equilibrium. The Cahn-Hilliard equations can be modified making the mobility concentration-gradient dependent to capture the nonequilibrium interface behavior. I will present experimental results for the Sn-Li2Sn5 transformation and discuss implications of nonequilibrium interface behavior for practical batteries.

P8: Mark Ilton - UMass Amherst

"Materials science of fast, impulsive motion"

Impulsive systems are typified by their repeatable energy storage and quick release of kinetic energy. Biological impulsive systems that achieve high velocities are typically small, and can use spring-like mechanical components to store elastic energy. Using a toy model to describe the dynamics of impulsive systems, we provide insight into the following questions: Why do some biological systems release energy from springs? Why are biological impulsive systems small? The decline of muscle output force at high velocity is an important factor determining when the storage and release of mechanical energy can provide an advantage. To understand how material properties affect the rate of energy release, we performed experiments on the free retraction of elastomers. Preliminary results suggest the stiffness, mass, and geometry of the elastomer affect the maximum speed of retraction

P9: Michael Imburgia - UMass Amherst

"Tuning reversible adhesion through materials properties and geometry"

The reversible adhesive systems of biological organisms are of particular interest to engineers as these systems can withstand substantial force when loaded, yet they require minimal energy to release. Here, we investigate the influence of system compliance in the loading direction on the adhesive force capacity for two different adhesive systems. We consider the significance of (i) loading multiple adhesive ‰ÛÏdigits‰Û� in parallel while varying inter-digit angular spacing and (ii) varying the degree of confinement between an elastomer-coated glass substrate and an isolated shear contact.

P10: Michael Jandron - Brown University

"Exploring Phononic Crystal Tunability using Dielectric Elastomers"

Phononic crystals are periodic, composite materials that exhibit phononic band gaps ‰ÛÒ frequency ranges in which elastic waves are prohibited. By using soft dielectric elastomers, which undergo large deformations when acted upon by an external electric field, the frequency ranges of band gaps may be altered. We present our numerical framework to solve these problems as well as some of our work on simulating circular inclusions in a square dielectric elastomer matrix. This work is currently funded through the US Navy‰Ûªs In-House Laboratory Independent Research (ILIR) program.

P11: Andrew Jones - MIT

"Shear Stress on Current and Structure of Electroactive Biofilms"

We develop a model for the impact of shear stress on an electroactive biofilm. An electroactive biofilm is a collection of exopolysaccarides, extracellular proteins, and bacteria that directly produce electricity. Our model incorporates existing evidence for an internal poroelastic structure of biofilms using Biot‰Ûªs model for stress on compressible poroelastic media. We compare our model with results from a rotating disk electrode for steady-state maximum current, porosity and height of the biofilm.

P12: Amir Kazemi Moridani - UMass Amherst

"Spectrally-engineered Polarized Thermal Emitters for IR Applications"

Periodic microstructures using nickel and gold depoition are fabricated on an elastomeric substrate by use of strain-induced buckling of the metallic layers. The intrinsically low emissivity of gold in the mid-infrared range is selectively enhanced by surface plasmonic resonance at the three different mid-infrared wavelengths, 4.5 åµm, 6.3 åµm, and 9.4 åµm. Moreover, as the emission enhancement effect exists only for the polarization perpendicular to the orientation of the microstructures, substantially polarized thermal emission of an extinction ratio close to 3 is demonstrated.

P13: Shaoting Lin - MIT

"Fringe instability in constrained elastic layers"

Soft elastic layers constrained between relatively rigid bodies appear abundantly in biological glues, joints and engineering applications including sealants, insulators, bearings, and adhesives. Here, we report a new mode of mechanical instability which we named as the fringe instability that occurs in constrained soft elastic layers. Through a combination of experiments, theory and numerical simulations, we quantitatively explain the fringe instability and derive scaling laws for its critical stress, critical strain and wavelength.

P14: Daren Liu - Brown University

"Size Dependence of the Yield Threshold in Dense Granular Materials"

Yield of dense granular materials is typically modeled by local, pressure-dependent criteria, in which yield at a point is assessed based only on the stress state at that point. However, nonlocal effects lead to phenomena that cannot be captured with local yield conditions. Here we consider whether the size-dependence of yield observed in inclined plane flow is configurationally general using 2D DEM calculations. We then show that the nonlocal granular fluidity model is capable of quantitatively capturing the observed size-dependent strengthening of thin granular bodies in all configurations.

P15: Liwei Liu - Brown University

"Study of Phase Boundary Kinetics in Silicon with Picosecond Ultrasonic"

Studying the kinetics of lithiation in crystalline silicon anodes will help in finding solutions to improve the efficiency of silicon-based electrodes in lithium battery systems. However, due to limitations in existing experimental methods, there is a lack of consensus on the real-time processes. Here we introduce a non-invasive, in-situ method to measure the displacement of the reaction front. We developed an apparatus integrating an electrochemical cell with Picosecond Ultrasonic. The measurements reveal relation between the state of charge and the rate of phase propagation.

P16: Michael McCarron - Boston University

"Cracking Sheets into Shapes: creating linear actuators with Kirigami"

Kirigami, the art of cutting paper, has long been seen as an intricate form of artwork and decoration, but recently, researchers are beginning to discover how it can be utilized in many engineering applications. Through geometry alone, the reactions of thin membranes containing cuts to tensile forces can be drastically changed. By introducing cuts in thin membranes, we have been able to generate non-linear motion from linear actuation. In our tests, we have seen rotation about the 3 Cartesian axes, and out of plane lift as the reactions of different cut patterns to an applied tensile force.

P17: Sabah Nobakhti - Northeastern University

"Correlation of the bone mineral density and the matrix elastic modulus"

Bone is a highly hierarchical composite material organized over several length scales. Protein deficiencies affect the cell functioning and collagen fiber arrangement at nanoscale, resulting in mineral and porosity alternation at microscale which influences the strength and toughness at the whole bone level. We explore the correlation of mineral density and the elastic modulus for pathologic mouse models and showd that they were not correlated at tissue level, explaining the need to investigate the underlying structure and compositional features at other levels of bone hierarchy.

P18: Anirban Pal - Rensselaer Polytechnic Institute

"Interlocking induced stiffness in stochastically microcracked material"

We explore a few restrained models for the molecular crystal cyclotrimethylene trinitramine (RDX) in the ë± phase. In particular, we investigate the effect of removing the flexibility of the molecule on various crystal-scale parameters such as the elastic constants, the lattice parameters, the thermal expansion coefficients, the stacking fault energy and the critical stress for the motion of a dislocation (the Peierls-Nabarro stress). To this end, a family of models with decreasing levels of molecular flexibility is developed.

P19: Nima Rahbar - Worcester Polytechnic Institute

Bioinspired design is used here to design super tough ceramics. Bioinspired multilayered samples with micron-size layers were fabricated using the freeze casting technique. a micromechanics model of the mechanical esponse of lamellar composites is presented. The closed-form solutions for the displacements as a function of constituent properties can be used to calculate the mechanical properties of lamellar-structured composite such as elastic modulus, strength and tensile toughness. The experimental results are in an excellent agreement with the analytical models.

P20: Vanessa Sanchez - Harvard University

"A Functional Apparel Approach for Soft Exosuit Design"

Recently, a major focus of wearable robotics has been the development of lower-limb exoskeletons to reduce the metabolic cost of walking. Many exoskeletons use a series of rigid linkages/interfaces to span the lower extremities and anchor to the human body. However, our lab incorporates lightweight and conformal functional apparel termed “soft exosuits” to apply joint moments via tensile forces in parallel with the muscles, thereby reducing the required muscular activation. The goal with soft exosuit interfaces is to use a structured functional textile to anchor to the human body in order to maximize comfort, minimize component migration on the body, and maximize power delivery. However, such a goal is challenging given the natural compliance of human tissue, sensitivity of human skin, and wide variability in human anatomy. This work aims to define functional design guidelines to maximize exosuit performance, with a particular focus on materials consideration, component patterning, and component fit. Participant testing is employed, where quantitative data of component performance, as well as comfort and usability feedback are collected. Through iterative cycles of testing and design improvements, the exosuit is further optimized.

P21: Adel Shams - New York University

"Pressure reconstruction in water impact problems"

As composite structures are increasingly integrated into marine vessels, the need for developing accurate models of fluid-structure interactions during hull slamming is great of interest. In this work, we seek to establish a physically-based understanding of the dynamic behavior of structures impacting water surface. To pursue this goal, first, we establish an experimental scheme to measure hydrodynamic loading using particle image velocimetry, second, we develop a mathematically-tractable model to study the hydroelastic response of flexible wedges via potential flow and Euler-Bernoulli theory

P22: Emily Tow - MIT

"Visualizing membrane fouling in osmotic desalination processes"

Cleaning of fouled reverse osmosis membranes is necessary in desalination plant operation, but the mechanisms of foulant removal are poorly understood. In situ visualization of the removal of synthetic biofilms from RO membranes reveals a mechanical instability: changing the ionic composition of the solution in contact with the deposited film causes it to swell, wrinkle, and detach. Rather than dissolving foulants, cleaning processes can be optimized to take advantage of the swelling properties of hydrogels and the resulting instability using only benign salt solutions.

P23: Zhengjin Wang - Harvard University

"Extrusion, slide and rupture of an elastomeric seal"

Elastomeric seals are widely used to block fluids of high pressures. Failure of the seals is costly and hard to predict. We studies a common mode of failure caused by a crack running through the length of a seal. We watch seals extrude, slide, rupture and leak in transparent, desktop experiments. We formulate theories to relate the desktop experiments to oilfield operations. The experimental results and theoretical predictions agree remarkably well.Our work shows that the elastic modulus, sliding stress, and fracture energy are principal factors that affect the leak resistance of seals.

P24: Felix Wong - Harvard University

"Physics of bacterial morphogenesis in Escherichia coli"

We model the dynamics of membrane bulging and lysis in Escherichia coli. We show that bulging can be energetically favorable due to the relaxation of the combined stretching energies of the inner membrane, cell wall, and outer membrane, and that experimentally observed bulge angles and eccentricities are quantitatively consistent with model predictions. We then show that the pressure-mediated bulk transport of external media into the cytoplasm agrees with a bulge-to-lysis timescale of seconds, after which lysis is consistent with both the membranes exceeding their yield areal strains.

P25: Wanting Xie - UMass Amherst

"Parametric Single Micro-Particle Impact Study in Cold Spray"

Laser induced single particle impact experiments were conducted to study the extreme dynamics of aluminum 6061 particles during individual impacts, and to provide precisely defined critical parameters for cold spray simulations. Single aluminum particles around 20um in diameter were accelerated up to 1km/s using high-power laser ablation. Accurate kinetic information of the impacting aluminum particles was acquired from the high-speed photographs. Cross sections were performed by FIB to investigate the microstructural change of the particle and the target under high-speed impact.

P26: Sina Youssefian - Worcester Polytechnic Institute

"Bioinspired Approach to Material Design of Cellulose-Based Composites"

Although many scientists have investigated the plasticizing effect of water on plant cell walls, the principle that controls the slight stiffening, observed at low moisture content (MC), is still unknown.We showed that this phenomenon occurs only occurs in the direction parallel to cellulose microfibrils. The formation of hydrogen bond bridges between lignin chains by water molecules and the consequent decrease in the fractional free volume of lignin nanostructure are found to be the main factors in enhancing the elastic modulus of cell walls at low MC.

P27: Hyunwoo Yuk - MIT

"Hydraulic Hydrogel Actuators and Robots"

We report a simple yet general method capable of assembling pre-shaped elastomers and hydrogels into hybrid structures with extremely robust interfaces and functional microstructures. The method is generally applicable to various types of commonly-used elastomers and diverse hydrogels. We further explore a number of novel applications taking advantage of the robust and microstructured hydrogel-elastomer hybrids including anti-dehydration hydrogel with elastomeric coating, stretchable diffusive hydrogel-elastomer microfluidics and stretchable hydrogel circuit on elastomer substrates.

P28: Kaizhen Zhang - Northeastern University

Lipid bilayer plays critical roles in various biological processes. Statistically, considerable efforts have been made to explore the mechanical behavior of lipid bilayers and their fusion mechanism. However, the characterization of an individual liposome and quantification of its fusion process are critical and urgent. Hence, AFM is introduced to directly apply and measure the external forces, involved in the characterization of a liposome and its fusion with a synthetic cell. As the result, the vesicle area expansion modulus, KA, and its fusion energy barriers are quantitatively determined.

P29: Mahdi Takaffoli - MIT

"Extreme stiffening of alginate hydrogels under cyclic loading"

Tailoring the mechanical properties of hydrogels can widen their applications in areas which demand higher or directional stiffness or strength. Here, we report an increase of about four times in stiffness of ionically crosslinked alginate hydrogels in response to cyclic tensile loading. Such observation is in contrast to the common softening response of soft materials, known as Mullins effect. The cycled material also exhibits anisotropic characteristics in parallel and perpendicular directions to the loading axis. Such uncommon behavior is explained based on the cyclically-induced network reorganization and the role of crosslinking zones in governing the mechanical response of alginate. TEM imaging of polymer chains provide direct evidence for the proposed physical interpretations of this phenomenon. Such stiffening can provide a processing technique to control the mechanical properties of alginates, fulfilling the demands in food and pharmaceutical industries for stronger alginate hydrogels.

P30: Levi Dudte - Harvard University

"Programming curvature using origami tessellations"

Mechanical metamaterials derived from planar tessellations of folds (origami) or cuts (kirigami) have been the subject of significant recent research efforts, with much focus on the interplay between homogeneous microstructure geometry and global mechanical and geometric response. We present recent work with generalized Miura-ori patterns and ongoing work with kirigami tessellations to produce surface materials with heterogeneous microstructure and programmed global shape, moving classes of fold and cut patterns toward flexible inverse design languages for mechanical metamaterials.