Short talk instructions
Keep in mind that your talk will only be 3 minutes.
Teaser Talk Session A
1) Levi Dudte - Harvard University"Using folds and cuts to program curvature and shape in mechanical metamaterials"
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.
2) Qiong Zhang - MIT"A Microscopic Description of the Granular Fluidity Field in Nonlocal Flow Modeling"
A recent granular rheology based on an implicit `granular fluidity' field has been shown to quantitatively predict many nonlocal phenomena. However, the physical nature of the field has not been identified. Here, the granular fluidity is found to be a kinematic variable given by the velocity fluctuation and packing fraction. This is verified with many discrete element simulations, which show the operational fluidity definition, solutions of the fluidity model, and the proposed microscopic formula all agree.
3) Daren Liu - Brown University"Size Dependence of the Flow 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.
4) Patrick Mutabaruka - MIT"On the modelling of complex granular flow within fluid"
Immersed granular avalanches have been investigated by many author and it has been shown, on packing fraction of granular bed point of view, that when the granular bed is tilted above his angle of repose, two regimes are evidenced: a loose regime where the slope fails spontaneously and a dense regime where the failure is delayed. Therefore, slop failure of a such medium was associated to the packing fraction at the peak of the stress state. We show that this behavior may be described in terms of the contact network anisotropy and how fluid act on the granular microstructure.
5) Kostiantyn Vasylevsky - University of New Hampshire"Comparison of Homogenization Approaches for Linearly Elastic Materials with Pores of Various Shapes"
Direct finite element analysis of periodic representative volume elements is utilized to evaluate several micromechanical models based on a solution for a single pore in anisotropic materials. It's shown that for several pore shapes, including spheroidal, polyhedral and irregular, Mori-Tanaka and Maxwell homogenization schemes are closer to the numerical results than non-interaction, self-consistent and differential models.
6) Vincenzo Gulizzi - Harvard University"Grain boundary formulation for polycrystalline micromechanics"
The talk presents an overview of a boundary element formulation developed for modeling damage and failure mechanisms occurring at the grain scale of polycrystalline materials. The salient feature of the formulation is the expression of the problem in terms of the grain boundary variables only, thus reducing the total number of degrees of freedom. Furthermore, if the non-linear behavior of aggregate is confined to the grain boundaries, the formulation does not need the volume mesh. Examples of intergranular microcracking and crystal plasticity are presented.
7) Anirban Pal - Ransselaer Polytechnic Institute"Stiffness in micro-cracked materials"
Two-dimensional randomly micro-cracked materials can exhibit stiffness beyond the transport percolation threshold due to the presence of topological interlocking. Thus, we introduce a new threshold to account for stiffness percolation, i.e. the fractional density of cracks at which the material fails to bear loads, and provide scaling exponents for the elastic modulus. Even with a linear constitutive law for the continuum, the material exhibits non-linear behavior between the
transport and stiffness percolation thresholds. We continue this study in three dimensions.
8) Paul Knysh - University of New Hampshire"Identification of post-necking hardening response of rate and temperature dependent metals"
A method for identifying the material hardening curves past the limit of necking in uniaxial tension across a range of strain-rates and temperatures in a fully-coupled way is proposed. Experiments on 304L stainless steel were performed using a custom isothermal testing setup. The identification procedure that includes FE model of the experiments is reduced to a mathematical optimization problem. Since the objective function in not available in closed form and is expensive to evaluate, an efficient optimization procedure that requires a limited number of function evaluations is proposed.
Teaser Talk Session B
1) Ruike Zhao - MIT"Multimodal instabilities on Curved Surface"
Most of the morphological patterns of bio-structure are developed on curved or tubular surfaces with distinct curvatures. Here, we investigate the surface instabilities and their evolution in bio-systems through a cylindrical bilayer structure. We construct phase diagrams for different surface curvature, showing the requirement of certain buckling or post-buckling instability on bilayer modulus distribution and mismatch strain. It is been proved that curvature plays an important role in determining surface morphologies.
2) Matteo Pezzulla - Boston University"Geometry and Instabilities in Growing Shells"
Growing structures can change shape either continuously or discontinuously. A bilayer spherical shell where the inner layer grows more than the outer layer will eventually snap and break symmetry at the same time. As a result, the final shape will not be an everted shell as it happens in the classical mechanical problem of the snapping induced by a poking force, but a buckled shell resembling the shape of a pollen grain during harmomegathy. Geometry entangles and explains the intricate connections among growth, buckling and snapping.
3) Anna Lee - MIT"Defect-controlled Buckling of Pressurized Spherical Shells"
We study the effect of a dimple-like geometric imperfection on the critical buckling load of spherical elastic shells under pressure loading. This investigation combines precision experiments, finite element modeling, and numerical solutions of a reduced shell theory, all of which are found to be in excellent quantitative agreement. Our primary focus is on providing a quantitative relation between its knockdown factor and the amplitude of the defect. In addition, we find that the buckling pressure becomes independent of the amplitude of the defect beyond a critical value.
4) Sabah Nobakhti - Northeastern University"Correlation of the elastic modulus to bone mineral density in pathologic mice"
Bone is a natural composite material made of mineral, organic collagen and water organized over several length-scales. Bone is strong and tough and its superior mechanical properties compared to other materials are believed to be due to its hierarchical organization. Characteristics of bone that are salient features of toughness were investigated in pathologic mouse models by measuring various structural and composition properties including crystal size and shape, mineral to collagen ratio, tissue level mineral and elastic modulus heterogeneity and correlated across multiple length-scales.
5) Flavia Libonati - MIT"Bio-inspired Composites: Using Nature to Tackle Composite Limitations"
This talk will present different aspects of my research on bone-inspired multiscale composite materials, from the study of bone to the design, fabrication and testing of new composites with improved mechanical properties. The talk will show different case-studies regarding the realization of new bone-inspired materials, by means of different manufacturing techniques, such as composite lamination and 3D-printing. This research involves the fundamental understanding of biological structural materials and the effective transferable technologies for the design and fabrication of novel materials.
6) Sai Deogekar - Rensselaer Polytechnic Institute"Networks of fibers with non-circular cross-section"
We study the mechanical behavior of 3D cross-linked random networks, composed of fibers with non-circular cross-section. Each fiber has a stretching mode and two bending modes of unequal stiffness, and the relative compliance of the three modes determine the dominant deformation mode. We find that for fibers with two distinct principle bending moduli, torsional stiffness plays an important role in determining the relative contribution of the two bending modes to the overall deformation. A relationship between the small scale network modulus and the structural parameters is established.
7) Zach Gault - Harvard University"Study of mechanical properties and memory formation in a transparent filled rubber"
Filled rubbers are composite materials consisting of crosslinked elastomers bearing colloidal particle aggregates. When the particle aggregates reach a critical volume fraction, they connect to create a subnetwork that both reinforces the elastomer network and introduces a characteristic low strain loss mechanism to the system. This loss mechanism, known as the Payne Effect, remains poorly understood. We demonstrate a transparent filled rubber with the potential to image the filler structure in situ by dispersing quantum dot tracer particles that conform to the filler subnetwork.
8) Nan Hu - Dartmouth College"Edge-effect Driven Bistability in Strained Si/Cr Bilayer Micro-claws"
In the spontaneous scrolling of a Si/Cr bilayer structure, two stable configurations were observed after the bilayer structure detached from the Si substrate. We employed both theoretical and computational models to study the multistable behavior of a Si/Cr nanohand and illustrate the mechanical principles involved. In both models, individual Si/Cr nanohands consistently demonstrate either monostability or bistability as the magnitude of the edge effect is varied. The results from this study provide a means to guide the on-demand design of strained nanostructures with tunable multistability.
Teaser Talk Session C
1) Wei Zeng - Dartmouth College"The virtual crack closure-integral technique (VCCT) implemented in CS-FEM for crack propagations"
The virtual crack closure integral technique (VCCT) is formulated in the framework of cell-based smoothed FEM (CS-FEM) for evaluating SIF‰Ûªs and for modeling the crack propagation. The mechanism of one-step-analysis feature of VCCT has been revealed mathematically based on the assumption of stress field equivalence. The approach requires no domain integration but attains same level of accuracy compared to the FEM-Q4 using interaction integral method. Numerical examples are provided to validate the effectiveness of the method and to predict the trajectories of crack propagations.
2) Jittisa Ketkaew - Yale University"Effect of Processing on Fracture Toughness of Bulk Metallic Glasses"
Bulk metallic glasses (BMGs) exhibits high strength and high elasticity, with a uniqueness of processing-ability. The ability to be shaped by thermoplastic forming (TPF) has given BMGs a lot of attention. Measurements of fracture toughness of BMGs have been difficult due to scattering of collected data as a result of processing condition, thermal history, uncontrolled porosity. Here,we utilize the novel TPF in combination with photolithography methods for mold fabrication which eliminate uncontrolled factors coupled in traditional processing method and able to limit the scattering to 3%.
3) Eddy Momanyi - University of New Hampshire"Necking suppression by Continuous-Bending-Under-Tension (CBT) of metal strips"
Continuous-Bending-Under-Tension (CBT) is an experimental technique that increases elongation-to-fracture by over 260% for mild steel, as compared to uniaxial tension. In CBT, a strip experiences 3-point bending by a traversing set of rollers, while under tension. The process works by suppressing the strain localization that leads to necking and rupture in the conventional tension test. Understanding the science behind CBT and developing a predictive framework will aid in processing hard-to-form materials, as are many of the materials intended to be used for vehicle lightweighting applications
4) 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.
5) Mona Monsef - University of New Hampshire"The Toughness of Fractal Interfacial layer"
Fractal Koch layers with four number of recursions were designed and fabricated via a multi-material 3D-printer (Objet Connex260). Uniaxial tension and compact tension mechanical experiments were performed to study the failure mechanisms of the designs. Both analytical and finite element (FE) models were developed to predict the toughness of the Koch layer under uniaxial tension and compact tension. A scaling law was discovered for this fractal interfacial layer.
6) Emily Tow - MIT"Cleaning desalination membranes with a mechanical instability"
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.
7) Claas Visser - Harvard University"In-air microfluidics"
For the first time, we connect and integrate the fields of microfluidics and additive manufacturing with technology that we call In-air microfluidics (IAMF). We impact two liquid jets while flying in-air, which enables producing monodisperse emulsions, particles, and fibers with controlled shape and size (10 to 300 um) and production rates 100x higher than droplet microfluidics. IAMF also enables rapid deposition onto substrates, to form 3D printed (bio)materials in hierarchical multi-scale architectures.
8) Mihai Duduta - Harvard University"Dielectric Elastomer Actuators for Soft Robotics"
A multilayer fabrication method has been used to create crawling soft robots based on dielectric elastomer actuators. These actuators are created without the need for pre-stretch, eliminating the need for rigid components. Studies on inchworm robots show them to be the fastest dielectric elastomer actuator-based systems reported to date, capable of traveling faster than 1 body length / second. Most importantly, the devices are primarily soft and deformable, with few rigid attachments.