PLENARY LECTURERS
Plenary lectures will be delivered by prominent figures of great scientific reputation in the field of mechanics of materials. To date, the following scientists have confirmed their participation.
Professor Markus J. Buehler
Professor of Civil and Environmental Engineering
Massachusetts Institute of Technology, USA
SUMMARY
Markus J. Buehler is the McAfee Professor of Engineering at MIT (an Institute-wide Endowed Chair), a member of the Center for Materials Science and Engineering, and the Center for Computational Science and Engineering at the Schwarzman College of Computing. He holds academic appointments in Mechanical Engineering and Civil and Environmental Engineering. In his research, Professor Buehler pursues new modeling, design and manufacturing approaches for advanced biomaterials that offer greater resilience and a wide range of controllable properties from the nano- to the macroscale. His interests include a variety of functional material properties including mechanical, optical and biological, linking chemical features, hierarchical and multiscale structures, to performance in the context of physiological, pathological and other extreme conditions. His methods include molecular and multiscale modeling, design, as well as experimental synthesis and characterization.
His particular interest lies in the mechanics of complex hierarchical materials with features across scales (e.g. nanotubes, graphene and natural biomaterial nanostructures including protein materials such as intermediate filaments and hair, collagen, silk and elastin, and other structural biomaterials). An expert in computational materials science and AI, he has pioneered the field of materiomics, and demonstrated broad impacts in the study of mechanical properties of complex materials, including predictive materials design and manufacturing. Between 2013-2020, Buehler served as Department Head of MIT’s Civil and Environmental Engineering Department. He has held numerous other leadership roles at professional organizations, including a term as President of the Society of Engineering Science (SES).
PLENARY LECTURE
Attention-based molecular modeling of hierarchical bio-inspired nanocomposites and protein materials
A combination of large-scale computational modeling, material informatics, and artificial intelligence/machine learning provides a powerful set of tools to understand, visualize and design novel materials with superior mechanical properties. In this talk we demonstrate applications to model and design materials, and to leverage material manufacturing for advanced mechanical properties. Through the use of nanotechnology and additive manufacturing, and bio-inspired methods, we can now mimic and improve upon natural processes by which materials evolve, are manufactured, and how they meet changing functional needs. We show how we can use mechanics to fabricate innovative materials from the molecular scale upwards, with built-in bio-inspired intelligence and novel properties, while sourced from sustainable resources, and breaking the barrier between living and non-living systems. This integrated materiomic approach is revolutionizing the way we design and use materials, and impacts many industries, as we harness data-driven modeling and manufacturing across domains and applications. The talk will cover several case studies covering distinct scales, from composites to biomaterials to food and agriculture, including hierarchical engineering. We review several critical methodological advances, including multiscale attention models, generative diffusion models, and integrated atomistic-to-continuum descriptions, applied to a range of material classes from protein materials to nanocomposites.
Professor Norman A. Fleck, FREng, FRS
Professor of Mechanics and Materials Engineering Department
University of Cambridge, UK
SUMMARY
Norman Fleck is a Professor whose research concerns the mechanical behaviour of solids under different conditions at the microscopic level. His major contributions have arisen in the area of novel materials and their applications in a wide range of activities, including the aerospace, automotive and construction industries. Examples include his studies of failure under compression in fibre-reinforced composites, a combination of waste cellulose fibres, such as sawdust, and polymer resin.
Norman is also known for his work on the properties of metal foams — air-filled materials that have potential as impact absorbers in cars — and on stiff but lightweight lattice materials that can be used in aircraft. Norman is notable for combining his theoretical understanding with enthusiasm for experiment and application. He is the recipient of numerous awards, including the 2013 Warner T. Koiter Medal from the American Society of Mechanical Engineers in recognition of his leadership in the international solid mechanics community, and an honourary doctorate from Eindhoven University of Technology, also in 2013.
PLENARY LECTURE
Multi-phase lattices: the role of an infilled phase
Lattice materials are finding increasing application due to recent advances in additive manufacture. It is now possible to invent and manufacture 2-phase lattice materials that comprise a cellular solid, fully infilled by a second phase. Alternatively, 3-phase lattice materials can be manufactured; they comprise 2 interpenetrating lattices in addition to porosity. Both classes of multi-lattice are explored in this talk. First, a 2D honeycomb or a 3D closed-cell Kelvin foam is filled with an inviscid, incompressible fluid that constrains the cellular solid to deform at constant volume. The incompressibility constraint has a major effect upon the compressive response of the 2D honeycomb but a minor effect upon the collapse of the Kelvin foam. The effect of infilling by a second phase of finite modulus and strength is also explored. In particular, it is shown that a core of sufficiently large modulus and strength will induce a switch in deformation mode of the lattice from non-affine bending to a stronger mode of affine deformation.
The effect of moisture upon the mechanical properties of a cellulose foam is also studied, with an emphasis upon the actuation behaviour of a pre-compressed foam. The foam re-actuates by a large uniaxial strain upon the addition of water. The mechanism of fluid imbibition is determined by a set of experiments to differentiate between diffusion and capillary flow, and to determine the kinetics of imbibition. The foam is also used to manufacture a lattice, and its morphing capability upon hydration is determined.
Professor Gerhard A. Holzapfel, Ph.D.
Professor of Biomechanics
Graz University of Technology Institute of Biomechanics, Austria
SUMMARY
Gerhard A. Holzapfel is Professor of Biomechanics and Head of the Institute of Biomechanics at Graz University of Technology (TUG), Austria, since 2007. He is also Adjunct Professor at the Norwegian University of Science and Technology (NTNU), Trondheim, Norway, and Visiting Professor at the University of Glasgow, Scotland. Until 2013 he was Professor of Biomechanics at the Royal Institute of Technology (KTH) in Stockholm, Sweden, for 9 years (7 years as an Adjunct Professor). After his PhD in Mechanical Engineering in Graz he received an Erwin-Schrödinger Scholarship for foreign countries to be a Visiting Scholar at Stanford University (1993-95). He achieved his Habilitation at TU Vienna in 1996 and received a START-Award in 1997, which is the most prestigious research award in Austria for young scientists. In the following years (1998-2004) he was the Head of a research group on “Computational Biomechanics” at TUG. Among several awards and honors in the past years he is listed in “The World’s Most Influential Scientific Minds: 2014” (Thomas Reuters), he received the Erwin Schrödinger Prize 2011 from the Austrian Academy of Sciences for his lifetime achievements, and he was awarded the 2021 William Prager Medal and the 2021 Warner T. Koiter Medal.
Professor Holzapfel’s research includes experimental and computational biomechanics and mechanobiology with an emphasis on soft biological tissues, the cardiovascular system including blood vessels in health and disease, therapeutic interventions such as balloon angioplasty and stent implantation, polarized light and second-harmonic imaging microscopy, magnetic resonance imaging and medical image processing; nonlinear continuum mechanics, constitutive (multi-scale) modeling of solids at finite strains such as cross-linked actin networks, growth and remodeling, nonlinear finite element methods, fracture and material failure. His research has been supported by TUG, Austrian Science Fund, Austrian Academy of Sciences, State of Styria, Österreichische Nationalbank (Jubiläumsfonds), Austrian Exchange Service, KTH, Swedish Research Council, National Institutes of Health (NIH), The Royal Society, Carnegie Trust, European Commission and the private industry.
PLENARY LECTURE
Mechanical Behavior of Human Aortic Walls and Ultrastructural Changes under Loading
Human aortic walls are composed of an extrafibrillar matrix, collagen, elastic fibers, and proteoglycans, while the active mechanical contribution is due to cells. The matrix can be considered as an isotropic material while the collagen fibrils/fibers create the anisotropy of the tissue. In general, collagen fibers are not perfectly aligned, but arranged in a rather dispersed structure for which a mean direction can be defined.
Note that the arrangement of the aortic tissue ultrastructure and the associated mechanical properties of tissue components can be severely damaged or even disrupted
by various diseases.
This lecture presents an approach to investigate the arrangement of ultrastructures in the aortic wall such as collagen fibrils and proteoglycans (PGs). The aortic ultrastructure is recorded using electron tomography and collagen fibrils and PGs are segmented using convolutional neural networks. The 3D ultrastructural reconstructions revealed a complex organization of collagen fibrils and PGs. The developed approach opens up practical possibilities, including quantifying the spatial relationship between nanoscale components as a function of the mechanical load. Several modeling aspects of the mechanical behavior of human aortic walls will also be presented from continuum mechanical and numerical perspectives. The non-symmetric collagen dispersion is considered while a focus is placed on the cross-linking of collagen fibers, resulting in a stiffening effect on the mechanical response.
Professor Stelios Kyriakides
Professor of Aerospace Engineering and Engineering Mechanics
University of Texas, USA
SUMMARY
Stelios Kyriakides received a B.Sc. degree in Aeronautical Engineering from the University of Bristol, U.K., and M.S. and Ph.D. degrees in Aeronautics from the California Institute of Technology. He is Professor of Aerospace Engineering and Engineering Mechanics at The University of Texas at Austin.
Kyriakides´ major technical interests are in the mechanics of solids, structures and materials, with an emphasis on instability of both structures and materials. His work is motivated by practical problems and usually involves combined experimental, analytical and numerical efforts. He has more than 275 publications, has co-authored two books, and has lectured extensively both nationally and internationally. He has pioneered propagating instabilities in structures such as offshore pipelines, bulges in elastic tubes, buckles in panels, and in materials such as fiber composites, shape memory alloys, cellular materials, wood, Lüders banding in metals, etc. He has significant contributions to plastic instabilities and crushing of structures, plasticity, forming problems in manufacturing, localization and ductile failure of metals, the mechanical behavior of composites, etc. He served as chair of the Executive Committee of the Applied Mechanics Division-ASME, as President of the American Academy of Mechanics (AAM), as chair of the US National Committee of Theoretical and Applied Mechanics, and is Editor of the International Journal of Solids and Structures. His recognitions include the Warner T. Koiter Medal from the American Society of Mechanical Engineers (ASME), Member of the US National Academy of Engineering, and Fellow of ASME and AAM.
PLENARY LECTURE
Compressive Behavior of Foams: Experiments and Modeling
Lightweight cellular materials such as foams exhibit excellent energy absorption characteristics and are widely used for impact mitigation in a variety of applications. This lecture presents results from combined experimental and analytical efforts that investigate the crushing behavior of Al-alloy open-cell foams under quasi-static uniaxial and triaxial loadings and under impact. The foam microstructure is established using X- ray tomography including the cell and ligament morphology. The compressive force- displacement response exhibits an initial stiff branch, followed by an extended load plateau during which localized cell crushing progressively spreads throughout the specimen. When most of the cells are crushed the densified material stiffens again. Foam crushing is simulated using micromechanically accurate models. Skeletal random models generated from soap froth using the Surface Evolver software are dressed with solid to match the material distribution and relative density of actual foams. The ligaments are modeled as shear- deformable beams with variable cross sections discretized with beam elements in LS-DYNA,
while the Al-alloy is modeled as elastic-plastic. Such models are shown to reproduce all aspects of quasi-static crushing faithfully including the initiation of instability, its localization, the subsequent propagation and the densification stage. This modeling framework is used to crush model foams in a true triaxial loading apparatus. The recorded responses are shown to exhibit the same three-deformation regimes characterized by stress plateaus and localized crushing. The results of such discrete models are used to calibrate a pressure sensitive constitutive model with a partially softening material response. It is demonstrated that such a homogenized solid, introduced in finite element analyses of triaxial crushing, can reproduce the responses and localized crushing observed in the discrete models. Under impact at velocities higher than 50 m/s, foams develop nearly planar shocks that propagate at well defined velocities crushing the specimen. The shock-impact speed and the densification strain-impact speed representations of the Hugoniot were both extracted directly from high-speed images recorded during the impact. The compaction energy dissipation across the shock was found to increase with impact speed and to be significantly greater than the corresponding quasi-static one. Similar discrete foam models used in impact simulations are found to capture accurately the dynamic crushing behavior observed experimentally. That is, limited inertial effects are present below a critical speed, and shock formation above it. In the shock regime the models reproduce the force acting at the two ends, the shock front velocity, and energy absorbed.
