Zdeněk P. Bažant
Northwestern University, USA
Lecture title: Design of New Materials and Structures to Maximize Strength at Probability Tail: A Neglected Challenge for Quasibrittle and Biomimetic Materials
Abstract: In developing new materials, the research objective has been to maximize the mean strength (or fracture energy) of material or structure and minimize the coefficient of variation. However, for engineering structures such as airframes, bridges of microelectronic devices, the objective should be to maximize the tail probability strength, which is defined as the strength corresponding to failure probability 10-6 per lifetime. Optimizing the strength and coefficient of variation does not guarantee it. The ratio of the distance of the tail point from the mean strength to the standard deviation depends on the architecture and microstructure of the material (governing the safety factor) is what should also be minimized. For the Gaussian and Weibull distributions of strength, the only ones known up to the 1980s, this ratio differs by almost 2:1. For the strength distributions of quasibrittle materials, it can be anywhere in between, depending on material architecture and structure size. These materials, characterized by a nonnegligible size of the fracture process zone, include concretes, rocks, tough ceramics, fiber composites, stiff soils, sea ice, snow slabs, rigid foams, bone, dental materials, many bio-materials and most materials on the micrometer scale. A theory to deduce the strength distribution tail from atomistic crack jumps and Kramer’s rule of transition rate theory, and determine analytically the multiscale transition to the representative volume element (RVE) of material, is briefly reviewed. The strength distribution of quasibrittle particulate or fibrous materials, whose size is proportional to the number of RVEs, is obtained from the weakest-link chain with a finite number of links, and is characterized by a Gauss-Weibull grafted distribution. Close agreement with the observed strength histograms and size effect curves are demonstrated. Discussion then turns to new results on biomimetic imbricated (or scattered) lamellar systems, exemplified by nacre, whose mean strength exceeds the strength of constituents by an order of magnitude. The nacreous quasibrittle material is simplified as a fishnet pulled diagonally, which is shown to be amenable to an analytical solution of the strength probability distribution. The solution is verified by million Monte-Carlo simulations for each of fishnets of various shapes and sizes. In addition to the weakest-link model and the fiber-bundle model, the fishnet is shown to be the third strength probability model that is amenable to an analytical solution. It is found that, aside from its well-known benefit for the mean strength, the nacreous microstructure provides a significant additional strengthening at the strength probability tail. Finally it is emphasized that the most important consequence of the quasibrittleness, and also the most effective way of calibrating the tail, is the size effect on mean structural strength.
Short-Bio: Born and educated in Prague (Ph.D. 1963), Bažant joined Northwestern in 1969, where he has been W.P. Murphy Professor since 1990 and simultaneously McCormick Institute Professor since 2002, and Director of Center for Geomaterials (1981-87). He was inducted to NAS, NAE, Am. Acad. of Arts & Sci., Royal Soc. London; to the academies of Italy (lincei), Austria, Spain, Czech Rep., India.and Lombardy; to Academia Europaea, Eur. Acad. of Sci. & Arts. Honorary Member of: ASCE, ASME, ACI, RILEM; received 7 honorary doctorates (Prague, Karlsruhe, Colorado, Milan, Lyon, Vienna, Ohio State); Austrian Cross of Honor for Science and Art 1st Class from President of Austria; ASME Medal, ASME Timoshenko, Nadai and Warner Medals; ASCE von Karman, Freudenthal, Newmark, Biot, Mindlin and Croes Medals and Lifetime Achievement Award; SES Prager Medal; RILEM L’Hermite Medal; Exner Medal (Austria); Torroja Medal (Madrid); etc. He authored eight books: Scaling of Structural Strength, Inelastic Analysis, Fracture & Size Effect, Stability of Structures, Concrete at High Temperatures, Concrete Creep and Probabilistic Quasibrittle Strength. H-index: 121, citations: 66,000 (on Google, incl. self-cit.), i10 index: 605. In 2015, ASCE established ZP Bažant Medal for Failure and Damage Prevention. He is one of the original top 100 ISI Highly Cited Scientists in Engrg. (www.ISIhighlycited.com). His 1959 mass-produced patent of safety ski binding is exhibited in New England Ski Museum. Home: http://cee.northwestern.edu/people/bazant/
Vienna University of Technology, Vienna
Tongji University, P.R. China
Lecture title: Multiscale Analysis of Concrete Structures
A Joint Research Project of Tongji University and Vienna University of Technology
The paper contains a report about a joint research project of Tongji University and Vienna University of Technology. Its title reads as “Bridging the Gap by Means of Multiscale Analysis”. The project was inspired by the tunnel, bridging the gap between the two parts of the Hongkong-Zhuhai-Macao Bridge (HZMB), bridging the gap between cities on opposite sides of the mouth of the Pearl River into the South Chinese Sea. The project stretches over the time period 2015-2019. It is financially supported by the Austrian Science Fund and the China Scholarship Council. The aim of the project is an assessment of the added value of multiscale analysis of tunnel segments by means of a comparison of results with the ones from experimental tests and with results from conventional structural analysis.
The following four topics will be treated in the lecture:
The project has
It is a good example of a meaningful blend of material mechanics of concrete and multiscale analysis of concrete structures.
Short-Bio: Born: January 5, 1942, Vienna, Austria; Dipl.-Ing., Civil Engineering, and Dr.techn., Vienna University of Technology (VUT) (1967 and 1970); University Assistant, VUT (1967-79); Fulbright Fellow (1971-72), Research Assistant (1973), Ph.D. (1974), all at Texas Tech; Max Kade Fellow, Cornell University (1975-76); Habilitation, VUT (1977); Visiting Research Associate, University of Tokyo (1979); Associate Professor, VUT (1979-83); UNIDO Field Expert, Zhengzhou Research Institute for Mechanical Engineering, China (1981); Prof., Head of Institute for Mechanics of Materials and Structures, VUT (1983-2010); Prof. Emer., VUT (10-2010-); National RPGE Chair Prof., Tongji Univ., Shanghai (2012-); Co-author of 8 books and 4 chapters of handbooks, co-editor of 16 books, author (co-author) of 226 journal papers and 280 proceedings papers, book chapters, etc.; 12 International/Foreign Prizes (including 2 Foreign Decorations) and 12 National Prizes (including 3 Young Investigator Awards and 4 Decorations); 6 Honorary Doctorates (Technical University of Cracow, Innsbruck, Kiev, Leoben, Prague, and Vilnius); 1 Honorary Professorship, Tongji University, Shanghai; Foreign Assoc. of CAE and NAE; Member of 3 European Academies of Sciences (and Arts) and of 15 National/Regional Academies of Sciences/ Engineering (in Austria, Croatia, the Czech Republic, Georgia, Germany, Hungary, Poland (Warsaw and Cracow), Portugal, Slovakia, in the Ukraine, and in the USA); President, Austrian Academy of Sciences (2003-06); Vice-President, Austrian Science Council (2010-2015).
Beijing Institute of Technology, P.R. China
Lecture title: Engineering Dynamics of Soft Machines
Abstract: The concept of soft machines covers a great variety of advanced industrial products, such as a soft robot handling fragile objects, a deployable solar sail and an airplane with morphing wings. Those soft machines are mainly composed of soft bodies, which are made of soft materials, including polyimide, silicon elastomer and electro-active polymer, so as to adapt to complex environments or missions. Furthermore, the soft bodies undergo not only large deformations, but also overall motions and frictional contacts with themselves or their environments.
This lecture presents the dynamic study on soft machines in the frame of multibody system dynamics. The study focuses on the efficient dynamic modeling of the geometrical nonlinearity of coupled overall motion and large deformation of a soft body, the physical nonlinearity of hyper-elasticity and elasto-plasticity, and interactional nonlinearity of frictional contacts or even entanglements of soft bodies, as well as the efficient dynamic computation algorithm of rigid-soft multibody system governed by a set of differential-algebraic equations of very high dimensions. The lecture illustrates the proposed approach via three case studies, i.e., the locomotion of a soft quadrupedal robot, the spinning deployment of a solar sail of spacecraft, and the deployment of a mesh reflector of satellite antenna, as well as the corresponding experimental studies.
Short-Bio: Prof. Haiyan Hu received Ph. D. in Solid Mechanics from Nanjing University of Aeronautics and Astronautics (NUAA), China in 1988. Then, he was a Humboldt Researcher Fellow at University of Stuttgart, Germany and a Visiting Professor at Duke University, USA successively. He received Professorship in Mechanics in NUAA in 1994, served as President of NUAA from 2001 to 2007, and President of Beijing Institute of Technology from 2007 to 2017.
Prof. Hu has made recognized contributions to the nonlinear dynamics and control of aerospace structures, including the delayed control of flexible structures, the nonlinear vibration isolation of missile stabilizers, the active flutter suppression of aircraft wings, and the deployment dynamics of space antennas. He was elected Fellow of The Chinese Academy of Sciences in 2007, Fellow of The World Academy of Sciences (TWAS) in 2010, and awarded Honorary Doctor of Science by Moscow State University, Russia in 2015 and by University of Reading, UK in 2016, respectively.
Jiun-Shyan (JS) Chen
University of Californian, San Diego, USA
Lecture title: Meshfree Methods: Progress Made After 20 Years and Future Directions
Abstract: In the past two decades, meshfree methods have emerged into a new class of computational methods with considerable success. In addition, a significant amount of progress has been made in addressing the major shortcomings that were present in these methods at the early stages of their development. For instance, essential boundary conditions are almost trivial to enforce by employing the techniques now available, and the need for high order quadrature has been circumvented with the development of advanced techniques, essentially eliminating the previously existing bottleneck of computational expense in meshfree methods. Given the proper treatment, nodal integration can be made accurate and free of spatial instability, making it possible to eliminate the need for a mesh entirely. Meshfree collocation methods have also undergone significant development, which also offer a truly meshfree solution. This presentation will give an overview of major progresses made in the field, the application to many challenging engineering mechanics problems, and the future directions of this research area.
Short-Bio: J. S. Chen is currently the Inaugural William Prager Chair Professor of Structural Engineering Department and the Director of Center for Extreme Events Research at UC San Diego. Before joining UCSD in October 2013, he was the Chancellor’s Professor of UCLA Civil & Environmental Engineering Department where he served as the Department Chair during 2007-2012. J. S. Chen’s research is in computational mechanics and multiscale materials modeling with specialization in the development of meshfree methods. He is the Past President of US Association for Computational Mechanics (USACM) and the Past Present of ASCE Engineering Mechanics Institute (EMI). He has received numerous awards, including the Computational Mechanics Award from International Association for Computational Mechanics (IACM), ICACE Award from International Chinese Association for Computational Mechanics (ICACM), the Ted Belytschko Applied Mechanics Award from ASME Applied Mechanics Division, the Belytschko Medal, U.S. Association for Computational Mechanics (USACM), among others. He is the Fellow of USACM, IACM, ASME, EMI, ICACM, and ICCEES.
Southern University of Science and Technology, China
Lecture title: Mechanics of interfaces in FRP-strengthened structures
Abstract: The performance of structures, particularly concrete structures, can be substantially enhanced through the external bonding of fiber-reinforced polymer (FRP) reinforcement in the form of thin laminates. In such an FRP-strengthened structure, the interface between the FRP laminate and the existing structure plays a key role in determining its behavior and strength. Indeed, extensive laboratory testing has demonstrated that failure of FRP-strengthened structural members often occurs by debonding of the FRP laminate from the existing structural member in a number of distinct modes. In this presentation, the speaker will provide a brief review of the intensive research undertaken over the past two decades on these debonding failure problems and a summary of the current understanding of interfacial mechanics in FRP-strengthened structural members that has resulted from this research. The major part of the presentation will be concerned with interfaces in FRP-strengthened concrete members, but interfaces in FRP-strengthened steel members will also be given due attention. The specific aspects to be covered include: (1) fundamental behavior of bonded interfaces; (2) classification of debonding failure modes; (3) debonding failure mechanisms and processes; (4) finite element and theoretical modelling issues; (5) design methods. The presentation will end with a brief discussion of future research needs.
Short-Bio: Professor Jin-Guang Teng is a Vice-President of Southern University of Science and Technology (SUSTech) and a Chair Professor at both SUSTech and The Hong Kong Polytechnic University (fractional appointment). He is an Academician of the Chinese Academy of Sciences, a Fellow of the Hong Kong Academy of Engineering Sciences and a Corresponding Fellow of the Royal Society of Edinburgh.
Professor Teng has conducted research on a wide range of topics across the broad field of structural engineering, including the structural use of fibre-reinforced polymer (FRP) composites in construction as well as steel and thin-walled structures. He has authored/co-authored over 200 SCI journal papers, leading to over 9,500 citations and an H-index of 50 according to the Web of Science Core Collection. Many of his research findings have been adopted by relevant design codes/guidelines in China, Australia, Europe, the United Kingdom and the United States. His research contributions have been recognized by many awards and prizes, including the State Natural Science Award of China, Distinguished Young Scholar Award from the National Natural Science Foundation of China, the IIFC Medal from the International Institute for FRP in Construction (IIFC), and the State-of-the-Art of Civil Engineering Award from the American Society of Civil Engineers.
Johns Hopkins University, USA
Lecture title: Uncertainty propagation from materials characterization to modeling
Abstract: Three-dimensional microstructures collected by experimental characterization provide both statistical information and the basis for computational models, which allows us to analyze heterogeneous materials at small length scales. However, the collection of such three-dimensional microstructural data commonly relies on destructive techniques, such as serial sectioning, and such methods often provide no quantitative measure of the accuracy of the digital microstructure in representing the true physical specimen. This makes quality assessment of the data sets difficult and it poses a challenge to identify which characterization parameters will produce optimal efficiency in the data collection process while maintaining an acceptable level of error in the resulting data. To address this question, this presentation describes a computational method that was developed to simulate serial sectioning data collection, based on a digital representation of a material, called a phantom. By simulating the data collection and data processing protocols of user defined parameters such as resolution, slice thickness, dwell time, polishing method, etc. the effect of each on error propagation can be tracked relative to the fully understood digital phantom. Then by varying each parameter the effects can be studied individually and provide bounds on both the contributions of each parameter to the error as well as the total error introduced through the experimental process. This provides a quantitative method for comparing the relative trade off between experimental parameters such collecting data at a very high resolution vs. collecting data over a large volume. Ultimately these measures are then utilized as part of an objective function to optimize the selection of experimental parameters. An example of optimization of experimental data collection parameters for the acquisition of an 3D Electron Backscatter Diffraction (EBSD) data set demonstrates how the error in computational models can be reduced.
Short-Bio: Lori Graham-Brady is Professor and Chair of the Civil Engineering Department at Johns Hopkins University, with secondary appointments in Mechanical Engineering and Materials Science & Engineering. She is also the Associate Director of the Hopkins Extreme Materials Institute. Her research interests are in computational stochastic mechanics, multiscale modeling of materials with random microstructure and the mechanics of failure under high-rate loading. She has been heavily involved in EMI, as a member of the EMI Board of Governors, as an Associate Editor for the Journal of Engineering Mechanics, and as the Chair of the EMI Probabilistic Methods Committee. She has received a number of awards, including the Presidential Early Career Award for Scientists and Engineers (PECASE), the Walter L. Huber Civil Engineering Research Prize, and the William H. Huggins Award for Excellence in Teaching.