Fractography of Glass

305 Pages·1994·9.851 MB·English

by  Brian R. Lawn, David B. Marshall (auth.), Richard C. Bradt, Richard E. Tressler (eds.)

Fractography of Glass
Fractography of Glass
Edited by
Richard C. Bradt
University ofA labama
Tuscaloosa, Alabama
and
Richard E. Tressler
The Pennsylvania State University
University Park, Pennsylvania
Springer Science+Business Media, LLC
Library of Congress Cataloging-in-Publication Data
Fractography of glass I edited by Richard C. Bradt and Richard E.
Tressler.
p. em.
Includes bibliographlcal references and index.
ISBN 978-1-4899-1327-2 ISBN 978-1-4899-1325-8 (eBook)
DOI 10.1007/978-1-4899-1325-8
1. Glass--Fracture. 2. Fractography. !. Bradt, R. C. IR1chard
Carll, 1938- II. Tressler, Richard E.
TA450.F73 1994
620.1'446--dc20 94-39370
CIP
ISBN 978-1-4899-1327-2
© 1994 Springer Science+Business Media New York
Originally published by Plenum Press, New York in 1994
Softcover reprint of the hardcover 1st edition 1994
All rights reserved
No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any
means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written
permission from the Publisher
PREFACE
This is a monograph of technical articles addressing
the fractography of glass. To introduce these articles,
it is appropriate to briefly discuss fractography and to
also address the issue of why glass is the focus of these
articles and this monograph. Perhaps part of the reason
is because fractography is concerned with the phenomenon
of fracture, and glass, having one of the lowest fracture
toughness values (resistance to fracture) of all
materials, is particularly prone to fracture or break.
Of course, glass has been prone to breakage ever since
the first glasses were produced many centuries ago.
However, the sciencejart of fractography has only evolved
over the last half century, at least in the modestly
quantitative form as we presently know it.
The word fractography does not appear in Webster's
finest. It probably originates from a combination of the
two terms: fracture and topography, deriving from the
Latin frangere and topographye. Fractography is the
study of the relief features or surface structure of
fractured surfaces, usually from an after-the-fracture or
post mortem perspective. Most modern fractography has
been pursued from the perspective of examining the broken
or fractured artifact, to attempt to reconstruct the
manner and to identify the reason why the object
fractured. As might be expected, in today's litigious
society, the fractographer, one who practices the sci"ence
of fractography, is in a modest degree of demand.
Without signaling individual articles, perhaps at
the expense of others, the chapters of this monograph are
organized in the way an object actually fractures. In
that respect, the text starts with information about
fracture origins, the growth of the original flaws or
defects and finally several papers addressing the
macroscopic fracture patterns which evolve. From this
latter viewpoint, both the fracture topography of the
v
vi PREFACE
actual fracture surface and the macrocrack pattern (at
right angles) are considered. Both perspectives are
equally important. As both o£ those pattern develop
ments are extremely complex dynamic fracture problems,
there is a lack of a fully analytical description in most
aspects of glass fracture.
Of course, fractography can be applied to materials
other than glasses, including minerals, metals and
composites. However, unlike the elastically isotropic
solid, glass, most of these other materials contain
microstructural features which complicate the fracture
phenomenon. So glass is the ideal material to embark on
an initial understanding of the many and varied dynamic
phenomena which create interesting features on fracture
surfaces. It is the wish of the editors that the papers
in this volume will serve as a beginning for all those
interested in fractography and particularly the
fractography of glass. Hopefully, these papers can serve
as a basis for the ongoing development of the fundamental
understanding of fracture phenomena in glass and perhaps
other materials as well.
We are grateful to the authors for their excellent
contributions and their pers~stence in completing their
manuscripts. We are appreciative of their patience and
understanding of the difficulties in bringing this volume
to its final form.
Richard C. Bradt
Tuscaloosa, AL
Richard E. Tressler
University Park, PA
CONTENTS
Indentation Fractography .•..•...........••••.•••..... 1
B.R. Lawn and D.B. Marshall
Quantitative Fractographic Analysis of
Fracture Origins in Glass ..•.......••..••..... 37
J.J. Mecholsky
Stress Wave Fractography ............••••...••....... 75
H.G. Richter and F. Kerkhof
Fractography of Stress Corrosion Cracking
in Glass .•••••.••........•...........••.••... 111
T.A. Michalske
Fractography of Optical Fibers .•••••.•...•......•.• 143
H.C Chandan, R.D. Parker and D. Kalish
Fractography bf Fiberglass .•...•.••....•.•......... 185
P.K. Gupta
The Fracture of Glass Containers ................... 207
J.B. Kepple and J.S. Wasylyk
Fracture and Fractography of Flat Glass ...........• 253
N. Shinkai
Contributors •..............•..•..••....•••..••..... 299
Index ..............•..••........••.....•.........• 301
vii
INDENTATION FRACTOGRAPHY
Brian R. Lawn
Center for Materials Science
National Bureau of Standards
Washington, DC 20234
David B. Marshall
Rockwell International ~c1ence Center
1049 Camino dos Rios
Thousand Oaks, CA 91360
1. INTRODUCTION
Indentation constitutes one of the most powerful test
techniques for the systematic investigation of deformation and
fracture responses in brittle materials. Indentations can be
used to evaluate critical mechanical parameters (toughness,
hardness, elastic modulus) with great simplicity and high
accuracy. They can be used to introduce controlled cracks into
strength-test specimens, and thence to obtain physical insight
into failure mechanisms. They can be taken as a base for
simulating "natural" surface damage processes such as particle
impact, abrasive wear and machining. In short, indentation
represents a model flaw system for quantifying a wide range of
mechanical properties. As such, it deserves detailed study.
Recourse to some of the review articles written on the
subject1- 8 reveals many facets of indentation analysis. For a
start, contacts may be considered either "blunt" or "sharp",
according to whether the local deformation prior to fracture is
elastic or elastic-plastic. The latter, if relatively complex in
its stress field characterization, presents us with some of the
more interesting new phenomena in brittle fracture. Second,
indentation events can occur under either equilibrium or kinetic
conditions of deformation and fracture. Of these, the first
Fractography ofG lass, Edited by R.C. Bradt and
R.E. Tressler, Plenum Press. New York, 1994
2 B.A. LAWN AND D.B. MARSHALL
lends itself more readily to detailed fracture mechanics
formulation, but the second takes us closer to engineering design
problems associated with "fatigue" (delayed failure) behavior.
Again, distinction may be· made between initiation and propagation
stages in the contact fracture evolution. Propagating cracks are
better understood because they develop in the contact far field,
where high stress gradients smooth out. The ultimate crack
configuration may nevertheless depend to a large extent on
exactly where in the near field the initiation occurs, which in
turn raises the question of availability of suitable starting
nuclei (e.g. whether such nuclei are pre-present or have to be
created by the contact process itself). We can devise many more
categories for the general indentation phenomenology, e.g. in
accordance with loading type (normal vs tangential) or loading
rate (static vs dynamic), attesting to a wide diversity in
underlying micromechanical processes.
In this chapter we consider these facets in relation to the
fractography of glass. We begin with surveys of blunt and sharp
contact patterns, describing basic features of the respective
morphologies and outlining the essential fracture mechanics
procedures for quantifying these features. If we pay more
attention to the sharp contact configuration, this is because of
the relatively dominant place it has occupied in indentation
testing over the past decade. We then consider the ways that
contact-induced cracks evolve when subjected to an ensuing
tensile stress, with their attendant implications on strength and
flaws. Finally, we look briefly at how indentation experiments
can be used to provide a base for modelling surface damage
processes related to wear, machining, etc. In some instances we
shall draw from studies on materials other than glass, both to
add to our insight into certain fracture mechanisms and to help
place the broad topic of indentation fractography into a wide
perspective.
2. BLUNT INDENTERS
If contact conditions remain entirely elastic up to the
onset of fracture the indenter is deemed "blunt"1• The classical
example is the Hertzian cone fracture produced by indentation of
a flat surface with a relatively hard sphere.9 A detailed
description of the evolution of Hertzian fractures was first
given by Frank and Lawn10. Initiation occurs from pre-existing
surface flaws in the region of high tensile stress just outside
the circle of contact; the ensuing crack encircles the contact
and subsequently propagates downward and outward into its fully
developed (truncated) cone configuration. As alluded to earlier,
the second, propagation stage is much easier to understand, and
so we shall deal with it first.
INDENTATION FRACTOGRAPHY 3
Fig. 1. Hertzian cone crack in soda-lime glass: (a) view from
beneath fully loaded specimen (light directed for
specular reflection); (b) view in profile, after
section-and-etch of unloaded specimen. After Ref. 13.
2.1 Crack Propagation
Under normal loading in an isotropic material like glass the
Hertzian configuration assumes near-axisymmetry.9- 12 Figure 1
shows top and section views of such a crack formed by a steel
ball of radius 12.7 mm on soda-lime glass.13 It is apparent that
the configuration can be closely represented as the frustum of a
cone. Once formed, the cone crack remains stable, although some
further, subcritical extension can occur under sustained loading
if moisture is present in the environment.
It is this stability of the fully propagating cone crack
which makes for simplicity in the fracture mechanics analysis.
Further increases in the indenter load over and above the
critical value for "pop in" simply cause the cone to expand its
circular base in a controlled manner;11 i.e. the configuration
satisfies the growth conditions for simple penny-like equilibrium
cracks, for which there is a standard solution14
P/c312 = A K (1)
2 c
where P is the load, c is the characteristic crack size, K is
the critical stress intensity factor for equilibrium exten~ion