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Reddy教授学术讲座的通告,关于设置美利坚合营国

五月 5th, 2019  |  永利总站手机版

报告题目:新材料和新结构在概率尾部的强度最大化设计:一个被忽视的准脆性材
料和仿生材料挑战 Design of New Materials and Structures to Maximize
Strength at Probability Tail: A Neglected Challenge for Quasibrittle and
Biomimetic
Materials报告时间:2018年10月30日15:00-17:00报告地点:7号楼二楼报告厅报
告 人:Zdenek P.
Bažant(美国科学院、工程院以及艺术科学院三院院士,铁木辛科奖章获得者,西北大学教授)欢迎广大师生参加土木与交通学院2018年10月26日报告人简介:Zdenek
P. Bažant was 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 1stClass 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 LHermite 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:
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
Kramers 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.附件:无

题 目:Non-local and Non-classical Continuum Models

时 间:2018年3月5日10:00-12:00

地 点:交通大楼604会议室

报告人:J.N. Reddy(美国德州农工大学,教授,美国工程院院士)

欢迎广大师生参加

土木与交通学院

2018年3月1日

报告人简介:

Dr. Reddy, the Oscar S Wyatt Endowed Chair Professor, Distinguished
Professor, and Regents Professor of Mechanical Engineering at Texas A&M
University, is a highly-cited researcher, author of 21 textbooks and
over 600 journal papers, and a leader in the applied mechanics field for
more than 40 years. Dr. Reddy has been a member of Texas A&M faculty
since 1992.

Professor Reddy is known worldwide for his significant contributions to
the field of applied mechanics through the authorship of widely used
textbooks on the linear and nonlinear finite element analysis,
variational methods, composite materials and structures, and continuum
mechanics. 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.

Recent Honors include: 2016 Prager Medal, Society of Engineering
Science, 2016 Thomson Reuters IP and Sciences Web of Science Highly
Cited Researchers – Most Influential Minds, and the 2016 ASME Medal from
the American Society of Mechanical Engineers, the 2017 John von Neumann
Medal from the US Association of Computational Mechanics. 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. A more complete resume with
links to journal papers can be found at

永利总站手机版,报告摘要:

Structural continuum theories require a proper treatment of the
kinematic, kinetic, and constitutive issues accounting for possible
sources of non-local and non-classical continuum mechanics concepts and
solving associated boundary value problems. There is a wide range of
theories, from higher gradient to truly nonlocal (e.g., strain gradient
theories, couple stress theories, Eringens stress gradient theories). In
this lecture, an overview of the authors recent research on nonlocal
elasticity and couple stress theories in developing the governing
equations of beams and plates will be presented. Two different nonlinear
gradient elasticity theories that account for geometric nonlinearity and
microstructure-dependent size effects are discussed. The first theory is
based on modified couple stress theory of Mindlin [1] and the second
one is based on Srinivasa and Reddy gradient elasticity theory [2].
These two theories are used to derive the governing equations of beams
and plates [3, 4]. In addition, a graph-based finite element framework
(GraFEA) suitable for the study of damage in brittle materials will be
discussed [5].

References of additional information

  1. Mindlin, R.D., Influence of couple-stresses on stress concentrations,
    Exper Mech. 3(1), 1-7, 1963.

  2. Srinivasa, A.R. and Reddy, J.N., A model for a constrained, finitely
    deforming, elastic solid with rotation gradient dependent strain energy,
    and its specialization to von Karman plates and beams, J. Mech Phys
    Solids, 61(3), 873-885, 2013.

  3. Arbind, A., Reddy, J.N., and Srinivasa, A.R., Nonlinear analysis of
    beams with rotation gradient dependent potential energy for constrained
    micro-rotation, Eur J Mech, A/Solids, 65, 178-194, 2017.

  4. Arbind, A., Reddy, J.N., and Srinivasa, A.R., Nonlinear analysis of
    plates with rotation gradient dependent potential energy for constrained
    micro-rotation, J Engng Mech, 144(2), 2018.

Khodabakhshi, P., Reddy, J.N., and Srinivasa, A.R., GraFEA: A graph
based finite element approach for study of damage and fracture in
brittle materials, Meccanica, 51(12), 3129-3147, 2016.

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