Prof. Zdeněk P. Bažant, Northwestern University, USA

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 Austria, Japan, Italy, Spain, Czech Rep., Greece, India and Lombardy, and Academia Europaea. Honorary Member of: ASCE, ASME, ACI, RILEM. Received: Austrian Cross of Honor for Science and Art; 7 honorary doctorates (Prague, Karlsruhe, Colorado, Milan, Lyon, Vienna, Ohio State); ASME Medal, ASME Timoshenko, Nadai and Warner Medals; ASCE von Kármán, Freudenthal, Newmark, Biot, Mindlin and Croes Medals, and Lifetime Achievement Award; SES Prager Medal; RILEM L'Hermite Medal; Exner Medal (Austria); Torroja Medal (Madrid); Solin and Bažant, Sr., Medals (Prague), etc. He is Illinois Registered Structural Engineer. He authored eight books: Scaling of Struct. Strength, Creep Eff. in Concrete Str., Inelastic Analysis, Fracture and Size Effect, Stability of Structures, Concrete at High Temp., Creep & Hygrothermal Effects, and Probab. Mech. of Quasibrittle Str. In 2015, ASCE established ZP Bažzant Medal for Failure and Damage Prevention. Citations: 71,000 citations on Google (incl. self-cit.), H-index: 127. In fresh Stanford U. weighted citation rankings, Bažant is #21 in CE #2 in Engineering overall--https://www.mccormick.northwestern.edu/civil-environmental/news/articles/2018/bazant-ranking.html

TITLE: Hydraulic Fracturing of Shale: Crucial Role of Weak Layers of Oriented Nano-Cracking Damage

ABSTRACT: Despite the sophistication and astonishing success of shale drilling technology, the percentage of natural gas extraction from gas shale strata remains too low, only about 5%. One reason doubtless is an insufficient understanding and control of the growth of the system of hydraulic cracks. For a long time it was believed that the overall permeability of shale mass to water or gas was drastically enhanced by preexisting natural cracks (by as much as 10,000 times). Recently, analysis of long-term secondary creep (or viscous flow) indicated that, despite propping by asperities, such cracks, whose average age is ~108 years, must have been closed (except for <15 nm opening) within 104--106 years and thus contribute virtually nothing to the gas extraction rate. It is shown that the explanation of enhanced permeability lies elsewhere. The natural crack must be enveloped by weak layers of oriented nano-cracks. This causes the poro-mechanical Biot coefficient of the weak layer to become highly anisotropic, which must lead to lateral cracks branching. According to the analysis of gas production rate at the wellhead, the spacing of the secondary branched cracks should be of the order of 0.1 m, far less than the spacing of initial hydraulic cracks, typically > 10 m. This new theory of hydraulic fracturing is supported by extensive finite element simulations with crack band model with damage described by the recently developed sphero-cylindrical anisotropic microplane model.

Prof. Alberto CarpinteriPolitecnico di Torino, Italy

Alberto Carpinteri received his Doctoral Degrees in Nuclear Engineering cum Laude (1976) and in  Mathematics cum Laude (1981) from the University of Bologna (Italy). He is a full professor in the Politecnico di Torino and Chair of Solid and Structural Mechanics, as well as the Director of the Fracture Mechanics Laboratory. During this period, he has held different positions of responsibility, among which: Head of the Department of Structural Engineering (1989-1995), and Founding Director of the Post-graduate School of Structural Engineering (1990-2014). 
He is presently the Head of the Engineering Division in the European Academy of Sciences (2016-).
Prof. Carpinteri was the President of different Scientific Associations and Research Institutions: the International Congress on Fracture, ICF (2009-2013), the European Structural Integrity Society, ESIS (2002-2006), the International Association of Fracture Mechanics for Concrete and Concrete Structures, lA-FraMCoS (2004-2007), the Italian Group of Fracture, IGF (1998-2005), the National Research Institute of Metrology, INRIM (2011-2013).
He is a Member of the Editorial Board of fifteen international journals, the Editor-in-Chief of the journal “Meccanica” (Springer, IF=1.949), and is the author or editor of over 900 publications, of which more than 400 are papers in refereed international journals (Scopus H-Index=52, more than 10,000 Citations) and 54 are books or journal special issues.
Prof. Carpinteri received numerous Honours and Awards: the Robert L'Hermite Medal from RILEM (1982), the Griffith Medal from ESIS (2008), the Swedlow Memorial Lecture Award from ASTM (2011), the Inaugural  Paul Paris Gold Medal from ICF (2013), the Doctorate Honoris Causa in Engineering from theRussian Academy of Sciences (2016), the Frocht Award from SEM (2017), the Honorary Professorship from Tianjin University (2017), and the Founding Fellowship from the Indian Structural Integrity Society (2018), among others.

TITLEMicro-damage instability mechanisms in composite materials: Cracking coalescence vs fibre ductility and slippage

ABSTRACT: Brittle solids often show an unstable structural behaviour represented by a negative slope in the load-displacement softening response. This means that the load must decrease to obtain a stable crack propagation. In extremely brittle cases, crack propagation occurs suddenly with a catastrophic drop in the load carrying capacity, and the load-displacement softening branch assumes a virtual positive slope. If the loading process is controlled by the displacement, the curve presents a discontinuity, and the representative point drops onto the lower branch with negative slope. In this case, both load and displacement must decrease to obtain a controlled crack propagation. Such a phenomenon, the so-called snap-back instability, was deeply investigated with reference to crack growth in quasi-brittle materials (Carpinteri, 1984; 1989). In the framework of Linear Elastic Fracture Mechanics, the cusp catastrophe represents the classical Griffith instability for very brittle systems.

Let us consider a tension test specimen where reinforcing fibres are embedded in the matrix, as illustrated in Figure 1a. In addition, let us consider the case of a specimen containing a distribution of collinear micro-cracks, as illustrated in Figure 1b. A load P is applied, opening the faces of an edge crack that propagates through the fibres or the collinear micro-cracks. Propagation will occur alternately within the matrix and through the heterogeneities (Carpinteri and Accornero, 2018; 2019). The loading process is controlled by the monotonically increasing crack length.

In both cases, the structural response presents a discrete number of snap-back instabilities with related peaks and valleys (Fig.1c). After each single peak, the crack starts growing in the matrix. Thus, the descending branches after peaks describe the crack growth between a fibre and the next, or between a micro-crack tip and the next. The crack arrests at the minimum of each valley, which represents the achievement of the next fibre or crack tip (Fig. 1a,b). The analogy between strengthened and weakened zones consists therefore in a multiple snap-back mechanical response, where descending branches of propagating cracks alternate with ascending (linear) branches of arrested cracks.

Figure 1. Regular distribution of reinforcing fibers in a brittle-matrix specimen with an edge crack (a); Brittle specimen with an edge crack and collinear micro-cracks (b); Load-displacement response diagram (c).

 

Ron Peerlings – Eindhoven University of Technology, Netherlands

Ron Peerlings is a faculty in the Department of Mechanical Engineering of Eindhoven University of Technology. His research interests include computational modeling of damage and fracture, microstructural modeling of plasticity and damage, homogenization, computational multiscale methods, higher-order continuum theories, and the mechanics of fibrous materials such as paper and fibre composites.

TITLE: Damage modelling of multiphase metallic materials from nano to macro scale

ABSTRACT: The formability of advanced engineering alloys may be limited by damage processes which occur at or near the internal boundaries separating the different phases which such materials generally contain. We address the issue at three distinct spatial scales. At the nano scale, the pile up of dislocations against a phase boundary causes in stress concentrations which may result in the nucleation of interface cracks. A computational approach based on the Peierls–Nabarro model of dislocations and a cohesive zone model for the phase boundary allows one to model this interaction in a natural fashion. At the scale of several individual grains, the nucleation and growth of interface cracks is conveniently modeled using spectral solver which employs a non local damage band along the grain/phase boundaries. And, finally, the material’s macroscopic formability is studied using a highly idealized model of the polycrystal, which allows one to systematically vary microstructural characteristics such as the mechanical contrast and morphology of the phases.

Prof. Cemal Basaran - University at Buffalo, The State University of New York

Dr. Cemal Basaran is a Professor in the Dept. of Civil, Structural and Environmental Engineering and the Director of Electronic Packaging Laboratory at University at Buffalo, The State University of New York.

He specializes in computational and experimental damage mechanics of electronics materials.  He has authored 140 + peer reviewed archival journal publications and several book chapters in the fields of damage mechanics.  His research includes development of the Unified Mechanics Theory, which is the unification of Newton’s universal laws of motion and the laws of Thermodynamics.  He is also interested in nano mechanics of 2-D electronic materials.  Some of his awards include 1997 US Navy ONR Young Investigator Award, and 2011 ASME EPPD Excellence in Mechanics Award. He is a Fellow of the ASME.  He has served and continues to serve on editorial board of 15 peer reviewed international journals, including IEEE Components, Packaging and Manufacturing Tech , ASME Journal of Electronic Packaging, ASCE Journal of Nanomechanics and Micromechanics, Entropy, as well as numerous other journals. He has been the primary dissertation advisor to 25 PhD students.

His research has been funded by NSF, ONR, DoD, State of New York, and many industrial sponsors including but not limited to Northrop Grumman, Raytheon, Delphi, Intel, DuPont, Texas Instruments, Micron, Tyco Electronics, Analog Devices and many others.

He serves as advisor to many national and international funding agencies around the globe.

TITLEDamage Mechanics Using the Unified Mechanics Theory

ABSTRACT: Newton’s three universal laws of motion make up the foundation for classical mechanics, and all subsequent theories of mechanics. However, Newton’s laws do not account for energy loss, dissipation or damage in a physical body.  However, thermodynamics governs dissipation and damage in all physical systems. Therefore, damage mechanics of any physical system, organic or inorganic, can be modeled using the thermodynamic laws.

Over the last 150 years, many unsuccessful attempts were made to unify the fields of classical mechanics and thermodynamics, in order to create a generalized and consistent theory of damage mechanics of inorganic and organic systems.   All past attempts to unify continuum mechanics and thermodynamics were based solely on curve fitting an empirical damage potential surface or a void evolution function to test data.

Unified mechanics theory unifies universal laws of motion of Newton and laws of thermodynamics with following equations,

Where  is a Thermodynamics State Index (TSI), which can have values between zero and one on a linearly independent separate axis. This requires modifying Newtonian space-time coordinate system by addition of this fourth axis. . As a results derivatives w.r.t. entropy are not zero.  TSI is directly calculated from the thermodynamic fundamental equation of the system, which accounts for all entropy generating micro mechanisms that contribute to damage mechanics failure criterion at hand. Calculation of TSI does not require any testing or a phenomenological damage potential surface or a void evolution model.  However, fundamental equation of the material must be derived analytically and must account for all entropy generating micro mechanisms.

Until recently, Boltzmann’s formulation of the second law of thermodynamics was assumed to be for gasses only. In this presentation, it will be shown, mathematically, that this not to be true. Damage evolution in solids follows the second law of thermodynamics in Boltzmann distribution.  We will go over Boltzmann’s [1877] mathematical proof.

Unified mechanics theory allows us to predict damage mechanics of any physical system, organic or inorganic, based on mathematical calculations without the need for a damage potential surface or void evolution function obtained by testing and curve fitting. In this presentation, recent advances in damage mechanics of materials using unified mechanics theory will be presented.

Prof. Lizhi Sun – University of California, Irvine, CA

Dr. Lizhi Sun is Professor of Department of Civil and Environmental Engineering (CEE) at University of California, Irvine (UCI). Dr. Sun’s primary area of research is the micro/nano-mechanics of heterogeneous composite materials, with applications in civil, mechanical, and biomedical engineering. He has published more than 100 peer-reviewed journal papers in the fields of mechanics and materials, applied physics, and biomedical engineering. He wins numerous academic and research awards such as Fellow of AAAS (2017), Fellow of ASCE’s Engineering Mechanics Institute (2014), UCI Civil and Environmental Engineering Professor of the Year (2013), AFRL Faculty Fellow (2011), UCI School of Engineering Fariborz Maseeh Best Faculty Research Award (2008), and Honda Research Initiation Award (2006). Dr. Sun is an editor for International Journal of Damage Mechanics, and associate editor for ASCE’s Journal of Engineering Mechanics.

TITLEMicrostructural damage characterization and chemo-mechanical degradation of freeze-thawed shotcrete

ABSTRACT: The study on durability of shotcrete under freeze-thaw action has become increasingly important for its extensive applications in construction and rehabilitation of damaged structures such as reinforced concrete retaining walls and repair of deteriorated bridges. In this research, we combine the nanoindentation and nano-CT technologies to characterize the evolution of microstructure in freeze-thawed shotcrete. Microcrack-density factor is introduced to describe the crack initiation and expansion in mortar matrix and interfacial transition zones. Furthermore, micromechanics-based modeling and simulation is established to quantify the effects of microstructure evolution on the elastic stiffness and strength degradation as well as degradation of chloride iron resistance. The damage and failure processes are categorized into three stages (crack initiation, stable crack growth and unstable crack propagation) during which the relation is quantified between F-T caused evolution in microstructure with degradation of released energy in cracking processes of shotcrete structure. Simulation results are compared with the experimental data in all three stages. It is shown that the proposed modeling framework can predict the aging of shotcrete in its fracture resistance under freeze-thaw actions.

Prof. Jie Li – Tongji University, Shanghai

Professor Jie Li is a Chair Professor in the Structural Engineering at Tongji University, and the director of Shanghai Institute of Disaster Prevention and Relief. He received his Ph.D. in Civil Engineering from Tongji University, China in 1988, and received an honorary doctorate degree in Engineering Science from Aalborg University, Denmark in 2013. Currently Prof. Li serves as a member of the director board of International Conference of Damage Mechanics (ICDM) and the president of International Association for Structural Safety and Reliability (IASSAR). Owing to his academic achievements in stochastic mechanics and reliability engineering, Professor Li was awarded the 2014 Alfred M. Freudenthal Medal by ASCE.

TITLEStochastic Damage Mechanics of Concrete: Background and Developments

ABSTRACT: As a typical heterogeneous quasi-brittle material, mechanical performance of concrete possesses two basic characteristics: nonlinearity and randomness. With a logical treatment of this knowledge, the stochastic damage mechanics of concrete has been systematically developed by the author and his collaborators in the past twenty years. The main achievements and recent developments are briefly reviewed in the lecture. 
In the context of theoretical frame of continuous damage mechanics, a  mesoscale random fracture model was proposed which is suitable for representing the multidimensional constitutive relation of concrete. In order to reveal the multi-scale damage evolution process of the model in micro-scale, a fine-scale investigation considering the correlation between nano-scale and micro-scale physical mechanisms had been carried out. Furthermore, the extension to constitutive models in the nature of dynamic damage and fatigue damage was performed, respectively. By means of the probability density evolution method (PDEM) proposed by the author and his colleague, nonlinear stochastic analysis and reliability assessment of concrete structures had been carried out in an elegant manner. It is shown that the stochastic damage mechanics of concrete provides a solid foundation for the reliability-based design and control of concrete structures.