Prof. Zdeněk P. Bažant, Northwestern University, USA

Born and educated in Prague (Ph.D. 1963), Baˇzant 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 Concrete and Geomaterials (1981-87). He was inducted to NAS, NAE, Am. Acad. of Arts & Sci., Royal Soc. London, the national academies of Austria, Japan, Italy, Spain, Canada, Czech Rep., Greece, India, Lombardy and Turin, Academia Europaea and Eur. Acad. Sci. & Arts. Honorary Member of: ASCE, ASME, ACI, RILEM. Received Austrian Cross of Honor for Science and Art I. Class from Pres. of Austria; 7 honorary doctorates (Prague, Karlsruhe, Colorado-Boulder, Milan, Lyon, Vienna, Ohio State); U. Minnesota); ASME Medal, ASME Timoshenko, Nadai and Warner Medals; ASCE von K´arm´an, Freudenthal, Newmark, Biot, Mindlin, TY Lin and Croes Medals, SES Prager Medal; Guggenheim Fellow; Outstanding Res. Award from Am. Soc. for Composites; RILEM L’Hermite Medal; Exner Medal (Austria); Torroja Medal (Madrid); etc. He authored nine books, on Scaling of Struct. Strength, Creep in Concrete Str., Inelastic Analysis, Fracture and Size Effect, Stability of Structures, Concrete at High Temp., Creep & Hygrothermal Effects, Probab. Mech. of Quasibrittle Str., and Quasibrittle Fracture Mechanics. H-index: 146, 90,000 cit. (Google). In 2019 Stanford U. weighted and filtered citation survey∗ (see PLoS), he was ranked worldwide no.1 in CE and no.2 in Engrg. In 2015, ASCE established ZP Baˇzant Medal for Failure and Damage Prevention. http://cee.northwestern.edu/people/bazant/

https://www.mccormick.northwestern.edu/civil-environmental/news-events/news/articles/2018/bazant-ranking.html

TITLE:Reformulation of Damage and Fracture Mechanics Required by Gap Test and Curvature-Resisting Sprain Energy 

ABSTRACT: Sixty-one years after Ray Clough’s epoch-making finite element analysis of cracks in Norfolk Dam1, there is still no completely satisfactory computational model for fracture and continuum damage. This is evidenced by recent model comparisons with many distinctive2 fracture tests, which are those that cannot be fitted closely by very different models and include the size effect, shear fracture and the new gap test6,7. The distinctive comparisons demonstrated severe limitations of the phase-field models3,4, dismal performance of peridynamics and severe   innate inadequacies of the nonlocal models of integral and gradient types, while the crack band model5 (CBM) with microplane M7 constitutive damage law performed well, though less than perfectly. As it transpired, the CBM performance be enhanced by introducing an energy, named the sprain energy Φ, which augments the strain energy Ψ and characterizes material resistance to the second gradient tensor of curvature of the displacement vector field, named the sprain tensor. This tensor differs from the strain gradient tensor and, importantly, includes the gradient of material rotation tensor. In FE discretization, the derivatives of Φ yield self-equilibrated sets of nodal or body sprain forces opposing excessive localization of softening damage. Subdividing the material characteristic length into a number of finite elements allows resolving the homogenized (or smooth) strain distribution across the width of the FE crack band. This leads to the smooth Crack Band Model8 (sCBM) which, along with M7, is found to capture the big effect of crack parallel stresses on both the fracture energy and the crack front width, as evidenced by the gap test6,7. Examples of FE fits of distinctive2 data are given. 

References

[1] Ray W. Clough (1962). The stress distribution in Norfolk Dam. Structures and Materials Series 100, IER Issue 19, Dept. of Civil Eng., Univ. of California Berkeley (134 pp.) (contract DA-03-050-Civeng-62-511, U.S. Army Engineer District, Little Rock). 
[2] Bažant, Z.P., and Nguyen, Hoang T. (2023), ``Proposal of a model index, MI, for experimental comparison of fracture and damage models." J. of Engrg. Mechanics ASCE; in press.
[3] Bažant, Z.P., Nguyen, H.T. and Abdullah Dönmez, A., 2022, ``Critical Comparison of Phase-Field, Peridynamics, and Crack Band Model M7 in Light of Gap Test and Classical Fracture Tests.” J. of Appl. Mech. 89: 061008, 1-26.
[4] Bažant, Z.P., Luo, Wen, Chau, Viet T., and Bessa, M.A. (2016). ``Wave dispersion and basic concepts of peridynamics compared to classical nonlocal models." J. of Applied Mechanics ASME 83 (Nov.) 111004, 1-16.
[5] Bažant, Z.P., Le, J.L. and Salviato, M., 2021, ``Quasibrittle Fracture Mechanics and Size Effect: A First Course” Oxford UP.  
[6] Nguyen, Hoang T., Pathirage, M., Cusatis, G., and Bažant, Z.P. (2020). ``Gap test of crack-parallel stress effect on quasibrittle frcture and its consequences." ASME  J. of Applied Mechanics 87 (July), 071012-1--11.
[7] Nguyen, H.T., Dönmez, A. A., Bažant, Z.P., 2021. ``Structural strength scaling law for fracture of plastic-hardening metals and testing of fracture properties." Extreme Mechanics Letters 43, 101141, 1-12.
[8] Zhang, Y., and Bažant Z.P., 2023, “Smooth Crack Band Model (sCBM)—a Computational Paragon Based on Unorthodox Continuum Homogenization.” J. Appl. Mech.041007.

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). After two years at the Consiglio Nazionale delle Ricerche, he was appointed Assistant Professor at the University of Bologna in 1980. He moved to the Politecnico di Torino in 1986 as a full professor, and became the Chair Professor 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).

Prof. Carpinteri was a Visiting Scientist at Lehigh University, Pennsylvania, USA (1982-1983), and was appointed as a Fellow of several Academies and Professional Institutions, among which: the European Academy of Sciences (2009-), the International Academy of Engineering (2010-), the Turin Academy of Sciences (2005-), the American Society of Civil Engineers (1996-). He is presently the Head of the Engineering Division in the European Academy of Sciences (2016-).

Prof. Carpinteri was the President of several 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).

Prof. Carpinteri was appointed as a Member of the Congress Committee of the International Union of Theoretical and Applied Mechanics, IUTAM (2004-2012), a Member of the Executive Board of the Society for Experimental Mechanics, SEM (2012-2014), a Member of the Editorial Board of fifteen international journals, the Editor-in-Chief of the journal “Meccanica” (Springer, IF=1.949). He is the author or editor of over 1,000 publications, of which more than 450 are papers in refereed international journals (G-Scholar H-Index=84, more than 29,000 Citations; Scopus H-Index=63, more than 14,000 Citations) and 58 are books or journal special issues.

Prof. Carpinteri received numerous international 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 the Russian Academy of Sciences (2016), the Frocht Award from SEM (2017), the Honorary Professorship from Tianjin University (2017), the Founding Fellowship from the Indian Structural Integrity Society (2018), and the “Pearl River” Professorship from Guangdong Province, Shantou University (2019).

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).

References

Carpinteri, A. (1984) “Interpretation of the Griffith instability as a bifurcation of the global equilibrium”, Proceedings of the N.A.T.O. Advanced Research Workshop on Application of Fracture Mechanics to Cementitious Composites, 287-316. Carpinteri, A. (1989) “Cusp catastrophe interpretation of fracture instability”, Journal of the Mechanics and Physics of Solids, 37:567-582. Carpinteri A., Accornero F. (2018) “Multiple snap-back instabilities in progressive microcracking coalescence”, Engineering Fracture Mechanics, 187:272-281. Carpinteri A., Accornero F. (2019) “The Bridged Crack model with multiple fibers: Local instabilities, scale effects, plastic shake-down, and hysteresis”, Theoretical and Applied Fracture Mechanics, 104:102351.

 

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.

TITLEMicromechanics of Failure in Multiphase Polycrystalline Materials – Experiments, Modeling and Application

ABSTRACT: The formability of advanced, multiphase engineering alloys may be limited by damage driven fracture. For the design of novel generations of such materials, it is paramount that we develop a better understanding, and predictive modeling, of the underlying micromechanical plasticity and damage mechanisms. We address this challenge by closely coordinated experiments and modeling. The experiments are based on samples which have locally been thinned to a few micrometers, so that the microstructure is practically uniform through the thickness. This allows us to construct finite element models which capture the full, three-dimensional microstructure of the region of interest in great detail and without the usual uncertainty on the subsurface microstructure. A dedicated crystal plasticity model has been developed to account for the heterogeneity of plastic deformation at the subgrain scale, as well as for nonstandard, highly orientation-dependent plastic mechanisms facilitated by the substructure of some of the phases of interest (i.c. martensite). If these phenomena are accounted for properly, an unprecedented agreement may be attained between the simulated deformation fields and those measured by digital image correlation in the experiments. For simulations of larger volumes, i.e. representative volume elements containing on the order of a hundred grains or more, the constitutive modeling may be simplified to three-dimensional isotropic plasticity combined with a planar, two-dimensional isotropic plastic mode. This, combined with a simple damage criterion, allows us to predict the necking based and damage based formability limits of the material using a single, pure shear simulation of the microstructure.

Prof. Jie Li – Tongji University, Shanghai

Prof. Jie Li is a Chair Professor in the Structural Engineering at Tongji University, the academician of the Chinese Academy of Science and European Academy of Science and Arts, and the director of Shanghai Institute of Disaster Prevention and Relief. He received Ph.D. in Structural Engineering from Tongji University, China in 1988, and received an honorary doctorate in engineering science from Aalborg University, Denmark in 2013. 
Prof. Li’s contributions are distributed in the area of stochastic dynamics, damage mechanics and engineering reliability. He is the author of six monographs and more than 400 peer reviewed journal papers. In 2014, Prof. Li was awarded the Alfred M. Freudenthal Medal by ASCE, owing to his academic achievements in the probability density evolution method and in the seismic reliability based design of large-scale infrastructure systems. 
Prof. Li currently serves as a member of the director board of International Conference of Damage Mechanics (ICDM), the Fellow of Engineering Mechanics Institute (EMI) and the vice president of Chinese Society of Vibration Engineering.

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.

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. 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.

Click Image to see the lecture

TITLEDamage Mechanics Using the Unified Mechanics Theory

ABSTRACT: Newton’s three universal laws do not account for, dissipation, or damage. However, the laws of thermodynamics govern dissipation and damage evolution. The unified mechanics theory unifies the universal laws of motion of Newton and the laws of thermodynamics at the ab-initio level. Therefore, the dissipation and damage mechanics of any system are included directly in the governing partial differential equation. However, to be able to unify these two sets of laws the Newtonian space-time coordinate system must be modified. Therefore, a new linearly independent fifth axis is introduced into the space-time coordinate system. The new axis is called the Thermodynamic State Index (TSI) axis which can have values between zero and one. When the entropy generation rate is maximum TSI coordinate is zero. When the entropy generation rate is minimum the TSI coordinate approaches the maximum value of one. The TSI axis is linearly independent, hence, the information represented on the TSI axis cannot be represented on the space-time coordinates. Moreover, the derivative of displacements with respect to entropy is no longer zero, as in classical continuum mechanics. The damage evolution along the TSI axis follows Boltzmann's formulation of the second law of thermodynamics. Therefore, the entropy generation rate must be calculated at each time increment at each material point. The entropy generation rate can be calculated directly from the thermodynamic fundamental equation of a material, which includes all entropy-generating micro-mechanisms that contribute to the failure criterion chosen. Unfortunately, thermodynamic fundamental equations for most materials are not readily available. The thermodynamic fundamental equation must be derived from the fundamental principles of physical chemistry accounting for all entropy-generating mechanisms. However, the analytical derivation of the thermodynamic fundamental equation does not require any testing for curve fitting a function. As a result, when the unified mechanics theory is used there is no need for an empirical damage potential surface or an empirical void evolution function, or parameters to determine damage evolution. Damage is defined as an evolution along the TSI axis according to the second law of thermodynamics as formulated by Boltzmann. In addition to the basic formulation of the theory, a verification of the theory, which was conducted and published independently, where Egner et al (2000) compared the Chaboche-Lemaitre ductile damage model with the unified mechanics theory-based model for the cyclic behavior of the P91 steel will be presented.

References

1-Cemal Basaran, Introduction to Unified Mechanics Theory with Applications, Springer Nature Switzerland AG, 2nd edition, 2023. 2- Władysław Egner, Piotr Sulich, Stanisław Mroziński, Halina Egner, Modelling thermo-mechanical cyclic behavior of P91 steel, International Journal of Plasticity, Volume 135, 2020, 102820, ISSN 0749-6419, https://doi.org/10.1016/j.ijplas.2020.102820.