CONFERENCE KEYNOTES

The IRF2020 program will include a number of Keynote Plenary Lectures by distinguished scientists in the different areas covered by the Main Topics and Symposia of the conference, to provide thematic presentations of their most recent findings.

To access the topics of the presentations and the the bio-sketches of the keynote speakers, please click on the corresponding picture..

Prof. Shaker Meguid

(Toronto University, Canada)

Professor Shaker Meguid is an internationally renowned scholar with significant contributions in computational and experimental mechanics at varied length scales. Undoubtedly, his research activities have contributed significantly to the areas of multiscale modelling, advanced and smart nanocomposites, crashworthiness, fracture mechanics and failure prevention. He has published 295 papers in leading tier-1 scientific journals, 240 presentations in international conferences of significance with a large number being invited as keynote and plenary speaker. He authored 4 books on fracture mechanics, nanomechanics and micromechanics, edited17 international conference proceedings and contributed 17 book chapters.

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Title of Presentation:

NOVEL FOAM-FILLED FRUSTA FOR VEHICULAR CRASH ATTENUATION: ANALYTICAL, NUMERICAL AND EXPERIMENTAL INVESTIGATIONS

Abstract:

Passive safety management using properly designed thin-walled energy absorbers remains the dominant approach adopted by the car industry to ensure the safety of the occupants in survivable car collisions. Among the various energy absorption devices, thin-walled metallic columns are the most widely used. This may be due to their excellent energy absorption capability, lightweight, cost effectiveness, high efficiency, and ease of manufacturing and installation. A major parameter that dictates the energy absorption capability of a shock absorber is the collapse mode. Unfortunately, however, thin-walled circular columns exhibit a variety of different collapse modes that include axisymmetric progressive folding, multi-lobe progressive folding, inversion, splitting, and global buckling.

In this presentation, Meguid will summarise his extensive research efforts, which are concerned with the crush behaviour of novel foam-filled conical frusta to overcome many of aforementioned challenges. In this research program, the foam-filled and unfilled frusta are treated analytically using kinematically admissible mechanisms, numerically using nonlinear elasto-plastic finite elements and experimentally using electrohydraulic servo-controlled test facility. The effect of key design parameters, such as - taper angle, slenderness ratio, and foam filling are carefully examined and discussed. The results show that introducing a taper angle in a straight column reduces the initial crippling load and increases the resistance to global buckling. Besides, the filling of the metallic foam further increases the specific energy absorption efficiency and dictates the resulting collapse mode of the absorber. This is due to the densification of the filler foam, its interaction with the column walls, and the reduction of the plastic fold length .

Dr. Reddy is a Distinguished Professor, Regents’ Professor, and inaugural holder of the Oscar S. Wyatt Endowed Chair in Mechanical Engineering at Texas A&M University, College Station, Texas. Dr. Reddy, an ISI highly-cited researcher, is known for his significant contributions to the field of applied mechanics through the authorship of 21 textbooks and nearly 700 journal papers. His pioneering works on the development of shear deformation theories (that bear his name in the literature as the Reddy third-order plate theory and the Reddy layerwise theory) have had a major impact and have led to new research developments and applications. Some of the ideas on shear deformation theories and penalty finite element models of fluid flows have been implemented into commercial finite element computer programs like ABAQUS, NISA, and HyperXtrude. In recent years, Reddy's research has focused on the development of locking-free shell finite elements and nonlocal and non-classical continuum mechanics problems, involving couple stresses, surface stress effects, micropolar cohesive damage, and continuum plasticity of metals.

Dr. Reddy has received numerous honors and awards. Most recent ones include: 2018 Theodore von Karman Medal from the Engineering Mechanics Institute of the American Society of Civil Engineers, the 2017 John von Neumann Medal from the U.S. Association of Computational Mechanics, the 2016 Prager Medal, Society of Engineering Science, the 2016 Thomson Reuters IP and Science’s Web of Science Highly Cited Researchers - Most Influential Minds, and 2016 ASME Medal from the American Society of Mechanical Engineers. He is a member US National Academy of Engineering and foreign fellow of Indian National Academy of Engineering, the Canadian Academy of Engineering, and the Brazilian National Academy of Engineering.

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Title of Presentation:

GRAFEA: A COMPUTATIONAL APPROACH TO FRACTURE AND DAMAGE IN SOLIDS

Abstract:

In this lecture, a graph-based finite element framework (GraFEA) for the study of fracture in solids is presented. GraFEA is built upon the fact that the finite element formulation for any hyperelastic continuum can be written in terms of the forces and strains along the edges of the elements. The major difference between GraFEA and continuum-based approaches to study fracture is that instead of placing the focus on the elements and introducing a displacement discontinuity either between or inside the elements, GraFEA focuses on nodes and the distance between the nodes. Fracture is merely introduced by breakage of the edges (any link between any two distinct nodes). Consequently, it will not suffer from the drawbacks of the existing continuum-based methods in the study of fracture. This provides us with a network representation of the finite element method (FEM), where the forces along the edges are represented in terms of the strains along the edges. However, there is a substantial difference between GraFEA and lattice networks: the force along each edge does not only depend on the strain along that edge, but on the strains along all of the edges surrounding that edge in the neighboring elements. Therefore, GraFEA is a nonlocal network and this is why it doesn't suffer from a limited Poisson's ratio (as is common with other lattice models for the study of fracture). Fracture and breakage of an edge is introduced into GraFEA using the idea of weakest link statistics, where the edge-based failure criterion is imposed directly on the discretized body. The weakest link statistics replaces the KIc approach with a critical zone size. At every step the strain (or force) along each edge, averaged over the critical zone, is compared with a critical value to check whether it is broken. The fracture criterion chosen in our study is a strain-based criterion; however, this is not a limitation of the method and other criteria can be applied. Several numerical examples are presented to illustrate the workings of GraFEA.

Dr. Noritsugu Umehara is a professor in the Department of Micro-Nano Mechanical Science and Engineering at Nagoya University, Japan. He has interests in both fundamental and applied aspects of manufacturing and tribology, especially in new polishing method of advanced ceramic materials using magnetic field and water lubrication.

He received his Bachelor, Master and a Doctorate of Engineering from Tohoku University, Sendai, Miyagi in 1983, 1985 and 1988, respectively. He began his carrier at Tohoku University in 1988 as a Research Associate in the Department of Mechanical Engineering prior to becoming Assistant Professor in 1993, Associate Professor in 1995. Professor Umehara joined Nagoya University as Professor in 2003. He publishes extensively in the relevant materials, manufacturing and tribology journals, and his scholarly work led to 6 Patents on Magnetic Fluid Grinding. He is regularly invited to give plenary and keynote lectures in international meetings and consults for the Japanese automotive industry. He directs the Advanced Manufacturing Laboratory in Nagoya University.

Dr.Umehara received the JSME Young Engineering award in 1991; 1995 LaRoux K. Gillespie Outstanding Young Manufacturing Engineer Award from the society of manufacturing engineers in 1995; F.W. Tayler Medal from the CIRP in 1995; and JSME paper award in 2010. He is a member of the Japan Society of Mechanical Engineers (JSME), the Japan Society for Precision Engineering (JSPE), the Japan Society of Tribologist (JAST) and the Japan Society for Grinding Engineering. He is also the current Chair of Micro-Nano Mechanical Science and Engineering Department, Graduate School of Engineering, and Adviser to the president of Nagoya University, Japan.

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Title of Presentation:

"FRICTIONLESS" DIAMOND-LIKE COATINGS AND IN-SITU OBSERVATION USING REFLECTANCE SPECTROSCOPY

Abstract:

Carbonaceous coatings, such as Diamond-Like Carbon (DLC) coating and amorphous Carbon Nitride (CNx) coating offer high hardness, low friction property and are affordable. Though it is reported in the literature that the transformed layer plays an important role in friction reduction, it is still unclear the mechanism(s) by which this low friction is developed.

Reflectance spectroscopy provides optical properties in the form of reflective index and extinction coefficient, as well as the thickness of each layer in a multilayer surface. This would allow us to analyze the properties of the transformed layer and the associated oil film. Specifically, in order to establish the effect of the transformed layer of CNx on friction, we developed novel in-situ observation technique using reflectance spectroscopy. The newly adopted reflectance spectroscopy technique facilitated the determination of the friction characteristics and allowed us to measures the friction force simultaneously. The reflectance spectrometer was set up appropriately to enable us measure the thickness, sp2/sp3 ratio and density of dangling bonds of the coating through sapphire hemisphere arrangement.

Our results reveal the reliability of our measurements technique as compared with our earlier works and other works that exists in the literature that estimate the friction coefficient. Additionally, this in-situ observation method with our reflectance spectroscopy was used to study the condition of two-phase lubricants, which is a mixture of two lubricants. Two-phase lubricants consist of low and high viscosity base oils, which are miscible at higher temperatures but not so at lower temperatures. However, it is difficult to know the separation condition in the thin lubricant film during sliding. We succeeded in measuring the separation of two lubricants in lubricant film using our reflectance spectroscopy.

Professor Zhang is currently a professor and the head of the Department of Aeronautics & Astronautics Engineering, School of Aerospace Engineering, Tsinghua University. He served as the Associate Editor of the International Journal of Mechanics and Materials in Design from 2014 to 2018. His research interests focus on numerical modeling of extreme events, such as hypervelocity impact, blast, bird impact, penetration and perforation, fluid-structure interaction. He has proposed several new efficient and stable meshless/particle methods and developed a 3D explicit and parallel material point method software, MPM3D, for numerical simulation of extreme events. He has published 4 monographs, 3 textbooks, and more than 150 journal papers, and was included in the list of Elsevier’s “Most Cited Chinese Researchers” since 2015.

Dr. Zhang was supported by the Program for New Century Excellent Talents in Universities, the Ministry of Education of China. He won the Qian Ling-Xi Achievement Award for Computational Mechanics in 2016, the ICACM (International Chinese Association of Computational Mechanics) Fellows Award in 2011 and Computational Mechanics Award in 2016, the Beijing Distinguished Teacher Award in 2015, second prize for Natural Science from the Ministry of Education of China in 2009, first prize for Natural Science from the Ministry of Education of China in 2008, and the Educational Innovation Award from Beijing Municipal Education Commission in 2003.

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Title of Presentation:

NUMERICAL SIMULATION OF EXTREME DEFORMATION PROBLEMS BASED ON MATERIAL POINT METHOD

Abstract:

Extreme deformation problems, such as hypervelocity impact, penetration, blast, machining, slope failure, sloshing and fluid-structure interaction problems, involve geometrical nonlinearity, material nonlinearity and boundary nonlinearity. The material undergoes extreme large deformation, fragmentation, melting, even vaporization, so that the conventional finite element method (FEM) encounters mesh distortion and element entanglement difficulties.

The Material Point Method (MPM), which makes use of both Lagrangian and Eulerian description of material, has demonstrated itself as an effective numerical method for modelling extreme events with large deformations. However, the original MPM suffers the cell crossing noise which makes the MPM not converging in some cases.

In this talk, the basic formulation of MPM, our recent developments on MPM, and our 3D explicit parallel code MPM3D developed for extreme deformation events simulation are briefly reviewed. Numerical examples are presented to demonstrate the application and capacity of MPM3D, which shows that MPM3D is a powerful tool for extreme deformation events simulation.