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Proceedings of an International Symposium on Absorbed Specific
Energy and Strain Energy Density Criterion, Budapest, September
1980. In memory of the late Professor Laszlo Gillemot"
The assessment of crack initiation and/or propagation has been the
subject of many past discussions on fracture mechanics. Depending
on how the chosen failure criterion is combined with the solution
of a particular theory of continuum mechanics, the outcome could
vary over a wide range. Mod elling of the material damage process
could be elusive if the scale level of observation is left
undefined. The specification of physical dimension alone is not
sufficient because time and temperature also play an intimate role.
It is only when the latter two variables are fixed that failure
predictions can be simplified. The sudden fracture of material with
a pre-existing crack is a case in point. Barring changes in the
local temperature,* the energy released to create a unit surface
area of an existing crack can be obtained by considering the change
in elastic energy of the system before and after crack extension.
Such a quantity has been referred to as the critical energy release
rate, G e, or stress intensity factor, K Ie. Other parameters, such
as the crack opening displacement (COD), path-independent
J-integral, etc. , have been proposed; their relation to the
fracture process is also based on the energy release concept. These
one-parameter approaches, however, are unable simultaneously to
account for the failure process of crack initiation, propagation
and onset of rapid fracture. A review on the use of G, K I, COD, J,
etc. , has been made by Sih [1,2].
Proceedings of First USA-Greece Symposium on Mixed Mode Crack
Propagation, Athens, Greece, 18-22 August, 1980
This International Conference on Analytical and Experimental
Fracture Me chanics was organized jointly by the Centro
Sperimentale Metallurgico, S. p. A. , Lehigh University and
Italsider S. p. A. It took place at the Hotel Midas Palace in Rome,
Italy, during 23-27 June, 1980. There were more than 150 attendees
from 19 different countries: Australia, Austria, Belgium, Canada,
People's Re public of China, Czechoslovakia, Finland, Federal
Republic of Germany, Hungary, Israel, Italy, Japan, The
Netherlands, Poland, Switzerland, Turkey, UK, USA and USSR. Dr. G.
M. Costa from Finsider officially opened the Conference and gave
the Welcome Address. More than 70 technical papers were presented
at three con current sessions. There were six plenary lectures that
helped to integrate the diverse efforts, e. g. , analytical
fracture mechanics, testing methods, metallur gical effects,
corrosion fatigue, dynamic crack propagation and weldments of in
dividual researchers. In addition to providing an overall view of
the current status of fracture mechanics technology, particular
emphasis was given to methods of controlling fracture in gas
pipeline structures. The members of the Organizing Committee made a
special effort to organize a panel discussion on the application of
fracture mechanics technology to the safe design of large diameter
pipelines. Dr. Michele Civallero from Italsider and Professor
George C. Sih from Lehigh University served as panel Co-Chairmen
and delivered survey lectures to stimulate questions from the
audience.
Concrete has traditionally been known as a material used widely in
the construction of roads, bridges and buildings. Since cost
effectiveness has always been one of the more important aspects of
design, concrete, when reinforced and/or prestressed, is finding
more use in other areas of application such as floating marine
structures, storage tanks, nuclear vessel containments and a host
of other structures. Because of the demand for concrete to operate
under different loading and environmen tal conditions, increasing
attention has been paid to study concrete specimens and structure
behavior. A subject of major concern is how the localized
segregation of the constituents in concrete would affect its global
behavior. The degree of nonhomogeneity due to material property and
damage. by yielding and/or cracking depends on the size scale and
loading rate under consideration. Segregation or clustering of
aggregates at the macroscopic level will affect specimen behavior
to a larger degree than it would to a large structure such as a
dam. Hence, a knowledge of concrete behavior over a wide range of
scale is desired. The parameters governing micro-and macro-cracking
and the techniques for evaluating and observing the damage in
concrete need to be better understood. This volume is intended to
be an attempt in this direction. The application of Linear Elastic
Fracture Mechanics to concrete is discussed in several of the
chapters."
This book contains results of more than a decade's effort on
coupled deformation and diffusion obtained in research performed at
the Institute of Fracture and Solid Mechanics, Lehigh University.
Despite the overwhelming number of theories on this subject, little
is known on the assessment of coupling effects because of the
inherent difficulties associated with experimentation. A case in
point is couple thermoelasticity, a theory that has remained
virtually unused in practice. This is indicative of the inadequacy
of conventional approaches. The interdependence of heat, moisture
and deformation arises in many engineer ing problems of practical
interest. Whether these effects are coupled or not depend on the
transient character of the boundary conditions. Special attention
is given to finding the coupling constants. Invoked is the
assumption that the physical parameters should be independent of
the specified boundary conditions. They can thus be extracted from
known experimental data for situations where coupling effects are
relatively weak and then applied to predict strong coupling effects
as boundary conditions are altered. This is illustrated for the
T300/5208 material commonly used in composites and permits a more
reliable evaluation of material behaving under extreme
environmental conditions. The lack of this knowledge can often be a
major deterrent to the achievement of new technological advances.
The reader will recognize that the material in this book does not
follow the main stream of research on moisture-temperature
diffusion and deformation."
An International Conference on the Application of Fracture
Mechanics to Ma terials and Structures was held at the Hotel
Kolpinghaus in Freiburg, West Ger many, June 20-24, 1983. It was
attended by more than 250 participants from different countries
which include Austria, Canada, Czechoslovakia, Democratic Republic
of Germany, Denmark, Federal Republic of Germany, Finland, France,
Greece, Hungary, Israel, Italy, Japan, Netherlands, Norway,
People's Republic of China, Portugal, Sweden, Switzerland, United
Kingdom, United States of America, USSR and Yugoslavia. Conference
Co-Chairmen were Professor G. C. Sih, Lehigh University, Bethle
hem, Pennsylvania, U. S. A., Dr. E. Sommer, Fraunhofer-Institut fur
Werkstoff mechanik, Freiburg, FRG and Professor W. Dahl,
Rheinisch-Westfalische Technische Hochschule, Aachen, FRG. Dr.
Wenrich, as the representative of the Land Baden-WUrttemberg,
delivered the opening address with the remarks that International
Conferences can serve the means to further enhance the technology
development of a country. He empha sized that the Federal Republic
of Germany is presently in need of strengthening the engineering
manpower in order to keep her in a competitive position. The
Conference was officially cast off with the leading plenary
lectures that under lined the theme of the technical lectures for
the first day. This pattern was observed for the five-day meeting.
The interplay between material and design re quirements was the
theme and emphasized in many of the technical presentations that
amounted to approximately ninety (90) papers."
Composites offer great promise as light weight and strong materials
for high performance structures. One of the major advantages of
these materials as compared with metals is the basic way in which
heterogeneity resist crack extension. In a fiber/matrix composite
system, the fibers tend to cause cracks to form at closer spacing
and delay the formation of a large crack. The enhancement of local
failure such as fiber breaking, matrix cracking and interface
debonding further reduces the energy level which might have
otherwise reached the point of catastrophic failure. Even though
substantial tests have been made on composite materials, little has
been gained in the understanding and development of a predic tive
procedure for composite failure. There are fundamental difficulties
associated with incorporating the nonhomogeneous and anisotropic
prop erties of the composite into the continuum mechanics analysis.
Additional uncertainties arise from voids and defects that are
introduced in the composite during manufacturing. Even a small
quantity of mechanical imperfections can cause a marked influence
on the composite strength. Moreover, the interface properties
between the fibers and matrix or bonded laminae can also affect the
load transmission characteristics significantly. It would be
impossible to establish predictive procedures for composite failure
unless realistic guidelines could be developed to control the
manufacturing quality of composite systems."
Following Volumes III and IV that dealt with the fracture mechanics
of concrete emphasizing both material testing and structural
application in general, it was felt that specimen size and loading
rate effects for concrete require further attention. The only
criterion that has thus far successfully linearized the highly
nonlinear crack growth data of concrete is the strain energy
density theory. In particular, the crack growth resistance curves
plotting the strain energy density factor versus crack growth known
as the SR.curves are straight lines as specimen size and loading
steps or rates are altered. This allows the extrapolation of data
and provides a useful design methodology. This book is unique in
that it is devoted specifically to the application of the strain
energy density theory to civil engineering structural members made
of concrete. Analyzed in detail is the strain softening behavior of
concrete for a variety of different components including the
influence of steel reinforcement. Permanent damage of the material
is accounted for each increment of loading by invoking the
mechanism of elastic unloading. This assumption is justified in
concrete structures where the effective stiffness depends primarily
on the crack growth rate and load history. Crack growth data are
presented in terms of SR-curves with emphases placed on scaling
specimen size which alone can change the mode of failure from
plastic collapse to brittle fracture. Loading rate effects can also
be scaled to control failure by yielding and fracture."
It is weH known that the traditional failure criteria cannot
adequately explain failures which occur at a nominal stress level
considerably lower than the ultimate strength of the material. The
current procedure for predicting the safe loads or safe useful life
of a structural member has been evolved around the discipline
oflinear fracture mechanics. This approach introduces the concept
of a crack extension force which can be used to rank materials in
some order of fracture resistance. The idea is to determine the
largest crack that a material will tolerate without failure.
Laboratory methods for characterizing the fracture toughness of
many engineering materials are now available. While these test data
are useful for providing some rough guidance in the choice of
materials, it is not clear how they could be used in the design of
a structure. The understanding of the relationship between
laboratory tests and fracture design of structures is, to say the
least, deficient. Fracture mechanics is presently at astandstill
until the basic problems of scaling from laboratory models to fuH
size structures and mixed mode crack propagation are resolved. The
answers to these questions require some basic understanding ofthe
theory and will not be found by testing more specimens. The current
theory of fracture is inadequate for many reasons. First of aH it
can only treat idealized problems where the applied load must be
directed normal to the crack plane.
This book consists of a collection of lectures prepared for a short
course on "Fracture Mechanics Methodology" sponsored by the
Advisory Group for Aerospace Research and Development (AGARD), part
of the North Atlantic Treaty Organization (NATO). The course was
organized jointly by Professor George C. Sih of the Institute of
Fracture and Solid Mechanics at Lehigh University in the United
States and Professor Luciano Faria from Centro de Mecanica e de
Materiais das Universidade de Lisboa in Portugal. It was held in
Lisbon from June 1 to 4, 1981. Dr. Robert Badaliance from the
McDonnell Aircraft Company in St. Louis and Dr. Oscar Orringer from
the Depart ment of Transportation in Cambridge are the other US
lecturers while Professor Carlos Moura Branco from Portugal also
lectured. The audience consisted of engineers from the Portuguese
industry with a large portion from the aeronautical sector and
others who are particularly interested to apply the fracture
mechanics discipline for analyzing the integrity of structural
components and fracture control methods. Particular. emphases were
given to the fundamentals of fracture mechanics as applied to
aircraft structures."
More than six years ago, several of Rabotnov's close friends and
colleagues from the USSR and USA decided to contribute a volume on
Plasticity and Failure of Solids in honor of his 70th birthday. The
celebration was interrupted unexpectedly by his death on May 13,
1985 at which time another decision was made still to publish the
work, but as a memorial volume. As in any field of scientific
endeavor, research confronts the scientists with anomalies; our
chosen area is no exception. The ways in which failure criteria and
plasticity theory are combined can differ widely among the
researchers; they will never yield quite the same results. Each of
the invited contributors has, therefore, been encouraged to express
his views and to expound on his personal opinion. The contributors
are free of enumeration from the authority and/or consensus of any
scientific society or community. What impedes scientific process is
the esoteric tradition of accepting ideas and theories by consensus
among members of societies and communities. The absence of such a
trend is refreshing; the collaboration between the authors from the
USSR and the USA had to be one of the contributing factors.
Finally, the editors wish to acknowledge the authors who have made
the publication of this volume possible. a. c. Sib S. T. Mileiko
AJ. Ishlinsky xi The late Professor Yuriy Nickolaevich Rabotnov
(February 24, 1914 - May 13, 1985) xii Scientific biography of the
late academician Yu. N.
What can be added to the fracture mechanics of metal fatigue that
has not already been said since the 1900s? From the view point of
the material and structure engineer, there are many aspects of
failure by fatigue that are in need of attention, particularly when
the size and time of the working components are changed by orders
of magnitude from those considered by st traditional means. The 21
century marks an era of technology transition where structures are
made larger and devices are made smaller, rendering the method of
destructive testing unpractical. While health monitoring entered
the field of science and engineering, the practitioners are
discovering that the correlation between the signal and the
location of interest depends on a priori knowledge of where failure
may initiate. This information is not easy to find because the
integrity of the physical system will change with time. Required is
software that can self-adjust in time according to the monitored
data. In this connection, effective application of health
monitoring can use a predictive model of fatigue crack growth.
Earlier fatigue crack growth models assumed functional dependence
on the maximum stress and the size of the pre-existing crack or
defect. Various possibilities were examined in the hope that the
data could be grouped such that linear interpolation would apply.
With the advent of the 80's there has been an increasing need for
analytic and numerical techniques, based on a thorough
understanding of microstructural processes, that express in a
manner suitable for practicing engineers the reliability of
components and structures that are being subjected to degradation
situations. Such situations fall within the framework offracture
mechanics, fatigue, corrosion fatigue and pitting corrosion.
Luckily, such techniques are now being developed and it was felt
timely to combine in one volume reports by the leaders in this
field who are currently making great strides towards solving these
problems. Hence the idea of this monograph was born and I am
pleased to be associated both with it and the contributors whose
chapters are included in this volume. A very large part of the
credit for this monograph must go to the authors who have taken
time out from their busy schedules to prepare their submissions.
They have all worked diligently over the last few months in order
to get their manuscripts to me on time and I sincerely thank them
for their help throughout the preparation of this volume.
Proceedings of a workshop on Composite Material Response:
Constitutive Relations and Damage Mechanisms, held at the Stakis
Grosvenor Hotel, Glasgow, UK, 30-31 July 1987
The International Conference on Fracture Mechanics in Engineering
Applica tion convened at the r ational Aeronautical Laboratory
(NAL) in Bangalore, India, March 26-30, 1979, with the presence of
approximately 400 scientists and engi neers. The participants
included individuals from all parts of India, United States of
America, United Kingdom, Japan, Holland, France, Hong Kong, Korea,
Sweden and Poland. The Conference was organized jointly by NAL,
Bangalore;and Lehigh University, USA. Various organizations in
India have also supported the Conference most generously. Professor
S. Dhawan, Director of the Indian Institute of Science and Secre
tary of Department of Space, delivered the inaugural speech. He
said that the advance of science was the precondition of the
development and survival of human society in the modern world. "It
is true that in recent times, science and tech nology - and their
practitioners - have been subjected to much public scrutiny, debate
and severe criticism." On the other hand, the depletion of
non-renewable resources, degradation of the natural environment and
a host of other problems had been laid at the door of technology
and science. One cannot deny that funda mental advances in the
physics and chemistry of the structure of matter had led to
spectacular engineering progress. Advanced technologies like
nuclear energy and space exploration were but expression of the
central role of computors, elec tronics, optics, polymers, etc.,
and all of these were heavily dependent on the successful
application of material science and technology."
Contained in the volume are the papers presented at an
International Symposium on Advanced Technology for Design and
Fabrication of Composite Materials and Structures. The Symposium
was organized by Consorzio per la Ricerca e l'Educazione
Permanente; Institute of Fracture and Solid Mechanics, Lehigh
University, Pennsylvania USA; Dipartimento di Ingegneria
Strutturale del Politecnico di Torino; and Dipartimento di
Ingegneria Aeronautica e Spaziale del Politecnico di Torino. It was
held at the Politecnico di Torino in Italy, May 24-28, 1993. The
support from the various organizations is acknowledged as follows:
* Consiglio N azionale delle Ricerche * ALENIA SP AZIO * AGUST A *
CIRA * AERMACCHI * Centro Ricerche FIAT * ALENIA (formerly
AERITALIA) * Collegio Costruttori Edili della Provincia di Torino
As new knowledge is being accumulated on the design and fabrication
of advanced composite systems in different sectors of the world,
there is the need not only to exchange new ideas but also to
disseminate the information from the researchers to the users. The
theme of this Symposium is particularly relevant to the automobile,
marine, aerospace and construction industry where the competitive
edge lies on improved processing and/or manufacturing of the
products. Technological advances have been and will continue to
depend strongly on the development of new materials and their
effective use in design. Empirical trial-and- error methods could
no longer be considered economically feasible when applied to
usage-specific materials such as composites.
Material technology has become so diversified in theories and the
construction of novel microstructures that the researchers and
practitioners are drifting further apart. This book is based on
material presented at an International Symposium in Xanthi, Greece
in July 1989. The symposium attracted a group of individual
engineers and scientists from the East and West who tackled the
question of why particular manipulations of a given material have
particular effects. Emphasis is laid on the strain energy function
because of the versatile role it plays in mechanics and physics. It
has been used successfully not only in predicting the failure of
solids but also in formulating constitutive relations in continuum
mechanics. The material presented falls within the areas of:
Fundamentals of Strain Energy Density, Damage Analysis on Strain
Energy Density, Strain Energy Density as Failure Criterion,
Applications, and Composites.
The Second USA-USSR Symposium on Fna~e 06 Compo~~e Mat~aGBPh took
place at Lehigh University, Bethlehem, Pennsylvania, during 9-12
March, 1981. This bilateral program between the U. S. and Soviet
Union was organized by Professor George C. Sih of the Institute of
Fracture and Solid Mechanics at Lehigh Uni versity and Dr. Vitauts
P. Tamuzs of the Institute of Polymer Mechanics of the Academy of
Sciences of the Latvian SSR in Riga. The First Symposium was held
in 1978 at Jurmala near the coast of Riga Bay. The primary reasons
for initiating this series of Symposia were to dissemi nate present
knowledge, to promote interchange of ideas, and to stimulate addi
tional studies on the development of composite materials between
the U. S. and USSR. Both countries have a vested interest in
developing the capability to assess and utilize the attractive
mechanical properties of composites so that they can be tailor-made
to meet specific design requirements. Despite the in creasing
number of published papers and articles, there is no communication
more effective than on a person-to-person basis. It is with this
objective in mind that a small group of engineers and scientists
from the U. S. and USSR have planned to meet every two years to
report recent progress on composite material research. The size of
this group is approximately sixty (60) participants. The
presentation involves about forty (40) technical papers which are
published in volume.
Experiments on fracture of materials are made for various purposes.
Of primary importance are those through which criteria predicting
material failure by deformation and/or fracture are investigated.
Since the demands of engineering application always precede the
development of theories, there is another kind of experiment where
conditions under which a particular material can fail are simulated
as closely as possible to the operational situation but in a
simplified and standardized form. In this way, many of the
parameters corresponding to fracture such as toughness, Charpy
values, crack opening distance (COD), etc. are measured. Obviously,
a sound knowledge of the physical theories governing material
failure is necessary as the quantity of interest can seldom be
evaluated in a direct manner. Critical stress intensity factors and
critical energy release rates are examples. Standard test of
materials should be distinguished from basic experi ments. They are
performed to provide routine information on materials responding to
certain conditions of loading or environment. The tension test with
or without a crack is among one of the most widely used tests.
Because they affect the results, with size and shape of the
specimen, the rate of loading, temperature and crack configuration
are standardized to enable comparison and reproducibility of
results. The American Society for Testing Materials (ASTM) provides
a great deal of information on recommended procedures and methods
of testing. The objective is to standardize specifications for
materials and definition of technical terms."
The planning meeting for a conference on Dynamic Crack Propagation
was held at M.LT. in February 1971 and attended by research workers
from several industrial, governmental and academic organizations.
It was felt that a more specialized meeting would provide a better
opportunity for both U.S. and foreign researchers to exchange their
ideas and views on dynamic fracture, a subject which is seldom
emphasized in national or international fracture conferences.
Dynamic crack propagation has been a concern to specialists in many
fields: continuum mechanics, metallurgy, geology, polymer
chemistry, orthopedics, applied mathematics, as well as structural
design and testing. It impinges on a wide variety of problems such
as rock breaking and earthquakes, pressure vessels and line pipes,
comminution and the per formance of armament and ordnance, etc.
Advances have been numerous, covering theories and experiments from
both the microscopic and macro scopic points of view. Hence, the
need for comparing the theoretical and experimental results and
bridging the gaps between the atomistic and continuum approaches
must be constantly emphasized. It also appeared that the overall
problem of dynamic fracture could benefit from a con solidation of
crack models proposed for the various types of materials: metals,
ceramics, composites, rocks, glasses, polymers and biomaterials.
The assessment of crack initiation and/or propagation has been the
subject of many past discussions on fracture mechanics. Depending
on how the chosen failure criterion is combined with the solution
of a particular theory of continuum mechanics, the outcome could
vary over a wide range. Mod elling of the material damage process
could be elusive if the scale level of observation is left
undefined. The specification of physical dimension alone is not
sufficient because time and temperature also play an intimate role.
It is only when the latter two variables are fixed that failure
predictions can be simplified. The sudden fracture of material with
a pre-existing crack is a case in point. Barring changes in the
local temperature,* the energy released to create a unit surface
area of an existing crack can be obtained by considering the change
in elastic energy of the system before and after crack extension.
Such a quantity has been referred to as the critical energy release
rate, G e, or stress intensity factor, K Ie. Other parameters, such
as the crack opening displacement (COD), path-independent
J-integral, etc. , have been proposed; their relation to the
fracture process is also based on the energy release concept. These
one-parameter approaches, however, are unable simultaneously to
account for the failure process of crack initiation, propagation
and onset of rapid fracture. A review on the use of G, K I, COD, J,
etc. , has been made by Sih [1,2].
The International Conference on Fracture Mechanics Technology
Applied to Material Evaluation and Structure Design was held in
Melbourne, Australia, from August 10 to 13, 1982. It was sponsored
jointly by the Australian Fracture Group and Institute of Fracture
and Solid Mechanics at Lehigh University. Pro fessor G. C. Sih of
Lehigh University, Drs. N. E. Ryan and R. Jones of Aeronau tical
Research Laboratories served as Co-Chairmen. They initiated the
organiza tion of this international event to provide an opportunity
for the practitioners, engineers and interested individuals to
present and discuss recent advances in the evaluation of material
and structure damage originating from defects or cracks. Particular
emphases were placed on applying the fracture mechanics tech nology
for assessing interactions between material properties, design and
opera tional requirements. It is timely to hold such a Conference
in Australia as she embarks on technology extensive industries
where safeguarding structures from pre mature and unexpected
failure is essential from both the technical and economical points.
view The application of system-type approach to failure control
owes much of its success to fracture mechanics. It is now generally
accepted that the discipline, when properly implemented, provides a
sound engineering basis for accounting in teractions between
material properties, design, fabrication, inspection and op
erational requirements. The approach offers effective solutions for
design and maintenance of large-scale energy generation plants,
mining machineries, oil ex ploration and retrieval equipments,
land, sea and air transport vehicles."
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