Astm stp 176 1955

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SYMPOSIUM ON
IMPACT TESTING

Presented at the
FIFTY-EIGHTH ANNUAL MEETING
AMERICAN SOCIETY FOR TESTING MATERIALS
Atlantic City, N. J., June 27 1955

ASTM Special Technical Publication No. 176

Published by the
AMERICAN SOCIETY FOR TESTING MATERIALS
1916 Race St., Philadelphia 3, Pa.

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FOREWORD
This publication is based on a Symposium on Impact Testing that was
held at the Fifty-eighth Annual Meeting of the American Society for Testing
Materials in Atlantic City, N. J., June 27, 1955 comprising the First and
Second sessions. The symposium was sponsored by Committee E-l on
Methods of Testing with Mr. F. G. Tatnall, Baldwin-Lima-Hamilton Corp.,
Philadelphia, Pa., serving as Symposium chairman.
Mr. Tatnall also presided at the Second session with H. L. Fry, Bethlehem
Steel Co., Inc., Bethlehem, Pa., as secretary and Mr. W. W. Werring, Bell
Telephone Laboratories, Inc., New York, N. Y., presided at the.First
session with W. H. Mayo, U. S. Steel Corp., Pittsburgh, Pa., as secretary.
In addition to the papers presented as a part of the Symposium, five other
papers, being appropriate to the general theme of the Symposium, have been
included on "Effects of Manganese and Aluminum Contents on Transition
Temperature of Normalized Nickel Steel," by T. N. Armstrong, and O. 0.
Miller, International Nickel Co.; "Low-Temperature Transition of Normalized Carbon—Manganese Steel," by T. N. Armstrong International Nickel
Co. and W. L. Warner, Watertown Arsenal; "Effect of Specimen Width
on the Notched Bar Impact Properties of Quenched-and-Tempered and
Normalized Steels," by R. S. Zeno, General Electric Co.; "Stress-Strain Relationships in Yarns Subjected to Rapid Impact Loading," by Herbert F.
Schiefer, Jack C. Smith, Frank McCrackin, and W. K. Stone, National
Bureau of Standards; and "Shock Testing with the Rocket-Powered Pendulum," by R. W. Hager, Sandia Corp.

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NOTE.—The Society is not responsible, as a body, for the statements
and opinions advanced in this publication.

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CONTENTS

PAGE

Introduction

1

Notched-Bar Testing—Theory and Practice—S. L. Hoyt

3

Discussion

7

Transition Behavior in V-Notch Charpy Slow-Bend Tests—Carl E. Hartbower
Discussion

10
23

Effects of Manganese and Aluminum Contents on Transition Temperature of Normal25
ized Nickel Steel—T. N. Armstrong and O. O. Miller
Low-Temperature Transition of Normalized Carbon-Manganese Steels—T. N.

40
Armstrong and W. L. Warner
Effect of Specimen Width on the Notched Bar Impact Properties of Quenched59
And-Tempered and Normalized Steels—R. S. Zeno.
Reproducibility of Charpy Impact Test—David E. Driscoll

70

Discussion
Automatic Impact Testing
S. DeSisto

75

From Room Temperature

to —236 C—Thomas
76

The Influence of Pendulum Flexibilities on Impact Energy Measurements—Joseph
I. Bluhm
84
Discussion

93

The Impact Tube: A New Experimental Technique for Applying Impulse Loads—
94
George Gerard
Discussion

110

Longitudinal Impact Tests of Long Bars With A Slingshot Machine—W. Ramberg
and L. K. Irwin
111
Discussion

125

Stress-Strain Relationships in Yarns Subjected to Rapid Impact Loading—Herbert
126
F. Schiefer, Jack C. Smith, Frank L. McCrackin and W. K. Stone
Shock Tester for Shipping Containers—W. H. Cross and Max McWhirter

141

Shock Testing with the Rocket-Powered Pendulum—R. W. Hager.

149

Properties of Concrete at High Rates of Loading—D. Watstein.

156

Discussion.

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170


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STP176-EB/Jan. 1956

SYMPOSIUM ON IMPACT TESTING
INTRODUCTION
Over the years there have been many
discussions of the technique and significance of the impact test, including several
formal symposia.
The last Impact Symposium was held
in 1938. Much technical development
since that time has been attributed to
information contained in those symposium papers.
Now seventeen years later another Im
pact Symposium steps into a field that
is already brimming with interest and
activity. Some phases of this field carry
the designation "Environmental Testing."

Along this line, it was suggested some
time ago by members of the Impact

Committee, of Committee E-l, that papers on shock tests be included in this
symposium which would encompass impact in parts, components, and complete
structures, and not confine_the symposium to notched bar testing. This broadened scope has been undertaken with
what appears to be very beneficial enhancement of the parctical application
of the impact test
straining rates. The end result is an excellent balance between theory and experimental results.

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STP176-EB/Jan. 1956

NOTCHED-BAR TESTING—THEORY AND PRACTICE
BY S. L. HoYT1
to fully recognize the rigidity or the
stiffening effect, at the notch section,
This paper covers a few of the points which is caused by the third dimensional

thought to be especially significant in stress. This is the stress, amplified by the
handling the practical phases of brittle stress concentration, which must exceed
fracture.
the cohesive or brittle strength for brittle
When metallurgists and engineers were fracture to result. Attention became
first confronted with the brittle fracture centered on stress raisers, and the theory
of steel, it was thought that impact seems to have been that, since steel is
must be the cause. But leading experi- ductile, a slight deformation at the root
menters soon found this concept to be would relieve the stress, and that nothing
inadequate and, at the turn of the more was important. An example which
century, the notch was recognized in its brings out the effect of rigidity is the
true light and was introduced into formal failed forging, which while ductile with
tests of steel quality. At the same time, the single or standard-width test bar was
the energy absorbed in breaking the test brittle, with the same notch, when tested
bar was universally adopted as the meas- with the double-width bar. Another is
ure of quality; this led to the simple the Navy Tear Test,3 which gives a much
device of breaking the test bar by means higher transition temperature than the
of a swinging pendulum. Doubtless due Charpy keyhole test bar does with the
to the earlier notions, the test thus be- same notch acuity. Another misconcepcame commonly known as the "im- tion has been that steels having the same
pact test" and so perpetuated the idea tensile properties would all perform
that brittle fracture was the result of similarly in the presence of a notch. This
impact. This was in spite of demonstra- was negated at an early date by a formal
tions to the contrary, such as the work of and authoritative series of tests conConsidere,2 who found that increasing ducted by the German Society for Testthe strain rate simply raised the tem- ing Materials, the results of which were
perature at which brittle fracture oc- published in 1907.4 In more recent times,
curred.
Two other misconceptions impeded
3
R. H. Frazier, J. R. Spretnak, and F. W.
understanding of notch brittleness and Boulger, "Reproducibility of Keyhole Charpy
delayed the general acceptance of and Tear-Test Data on Laboratory Heats on

Steel," Symposium on Metallic Manotched-bar testing. First was the failure Semikilled
terials at Low Temperatures, Am. Soc. Testing
HISTORICAL BACKGROUND

1
Metallurgical
2

Consultant, Columbus, Ohio.
Considere, "Contribution a PltJtude de la
Fragility dans les Fers et les Aciers," (1904).

Mats., p. 286 (1953). (Issued as separate publication
ASTM STP No. 158.)
4
See for example, S. L. Hoyt, "Principles of
Metallography, McGraw-Hill Book Co., Inc.,
New York, N. Y., p. 226 (1920).

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4

SYMPOSIUM ON IMPACT TESTING

the fallacy of this assumption has been
demonstrated many times.
Thus, while stress concentrations were
recognized, the important effect of notch
rigidity was largely ignored and the easy
assumption was made that ductility
would provide steel with what was
needed to handle notch conditions. Impacts were held to be the prime service
hazard, which, of course, led to a further
discounting of the effects of notches.
This line of thought, except in a few
cases, set up a block to the correct understanding of "brittle fracture."
A major object in noting these details
of the history of brittle fracture is to
emphasize that the service problem has
been the brittle behavior and low energyabsorbing capacity of ductile steel.
Hence, the proper handling of this problem requires an understanding of the
conditions that produce the brittle failure. The problem of ductile failure under
notch conditions is much more complex,
less well understood, and furthermore,
seldom encountered in practice.
If steel retained its ductile behavior
under all conditions, as many non-ferrous metals do, the problem would be
one of mechanics of materials and not of
metallurgy. This is true of steel when it
is tested above its transition temperature, since such tests determine the behavior during, and as a result of, plastic
deformation of some severity. In reality,

the significant properties of the steel
must be those of the initial and undeformed condition, from which it follows
that to be fruitful, laboratory studies of
brittle fracture should develop the same
brittle behavior as is developed in service.
It is advanced here that these concepts
are vital to the selection of steel when
the service hazard is brittle fracture and
also to the interpretation of laboratory
test results.

STEEL SELECTION
A somewhat unusual example of
notched-bar testing to select a steel for a
specific application may be illustrated
by means of a hypothetical case. It is discussed to illustrate how these principles
can be employed.
In this example, a weldment made of
common steel was exhibiting brittle
failures at — 30 F. When tested with the
V-notch Charpy bar, the 10 ft-lb transition temperatures of a group of these
steels ran from 30 to 90 F, all temperatures being idealized for purposes of discussion. At the service temperature of
— 30 F, all of the steels tested including
some of presumably "better" quality,
were completely brittle. While one could
say that one steel was better than
another, there was no way of interpreting
the results to decide which steels, if any,
were "good enough" for the application.
Obviously, these transition temperatures

do not give a sound basis for selecting the
proper steel to use. At this stage of the
example, there was no opportunity to
secure samples from a known satisfactory
weldment for test purposes.
According to one theory, one could
assume that the steel should have a
transition temperature, with the standard bar, which came at a safe margin
below —30 F. While that might be a safe
steel to apply, there would still be no
assurance that it would be "good
enough" or, what is more important in
industrial practice, that it would be
"just good enough." Furthermore, a
glance at steel costs would show that a
steel with that low a transition temperature would price the weldment off the
market. So it became necessary to seek
the solution by other means.
A search through past records suggested that some steels were performing
better than others under much the same
conditions. This revealed that the weld-

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HOYT ON NOTCHED-BAR TESTING
ment was differentiating between steels
at — 30 F, whereas the Charpy test was

not. This indicated a possibility of developing a test bar, with a less drastic
notch effect than that of the V-notch
bar, which would differentiate between
the steels at — 30 F as the weldment did.
That test bar could be used as a model
or a guide and, in additional testing,
make it possible to select the cheapest
steel that was "just good enough." In
this case, steel costs dictated that brittle
failure must be prevented by not letting
a fracture start and run, though that
placed the burden on design, fabrication,
and inspection.
With reference to transition-temperature testing for selecting the steel, it
maybe noted, first, that there was noway
of knowing whether to use steel with a
transition temperature of 0 F, — 30 F, or
— 60 F, etc., and, second, that the costs
of these steels vary so much that a wrong
choice could be fatal.
The element of cost is so important in
steel selection that a special study is
frequently called for. In one case, it was
found that a better steel, although it
cost more per ton, was also stronger than
the steel it was to replace and, therefore,
would give a weldment of the same
strength that would be lighter, less expensive, and less vulnerable to brittle
fracture than the cheaper and inferior
steel.

The case of steel for merchant ships
may be taken as another example of the
use of a notched-bar test of steel for
acceptability in a specific application.
It has been established that the plates in
which fracture started has a Charpy
V-notch value of about 10 f t-lb at the air
temperature at which failure occurred.
The corresponding value for. the plates in
which fracture stopped was about 20
ft-lb. Consequently, one can say that
acceptable steel should have values of
either 10 ft-lb or 20 ft-lb at the low expected service temperature, depending

5

on which approach is used. Steel for acceptance would then have to be tested
at only the one temperature. The justification of this procedure is the finding
that the V-notch bar is a reasonably
satisfactory replica of the ship structure,
which means that both break in essentially the same fashion at the same temperature. The V-notch for ship steel
corresponds to the special notch for
testing steel for the weldment at —30 F.
These are examples of the use of constant- or single-temperature testing for
engineering applications. The method is
that of determining and then using the
notched bar that approximates the component or structure to be tested, whether
the test bar is a so-called standard bar
or one developed specifically for the application. However, it is to be recognized
that in the latter case, the design may be

based on the principle of insuring against
starting a fracture and that, therefore, the
steel thus selected may not have the
ability to stop a fracture from running.
If one does not rely on avoiding starting
a fracture, then a steel should be used in
which a crack does not run under serious
conditions. The latter will usually be
more expensive.
RATING STEELS FOR
NOTCH TOUGHNESS
In the great majority of cases, different
notched bars rate a series of steels in
about the same order of merit. Consequently, studies of the effects of composition, heat treatment, and steelmaking practice generally employ some
one test bar for rating purposes. It is
well that this is so, and it points up the
first requirement of work on brittle
fracture, namely, that an effective notch
of some kind be used for testing. However, in some exceptions two different
test bars may give different ratings for
the same steel, and this raises the question of which to believe or use.
An example of the latter situation is

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6

SYMPOSIUM ON IMPACT TESTING

given by data of Christensen and Augland, which were recently cited by
Houdremont.5 These are reproduced in
Table I.
The V-notch rates steels Nos. 3 and 6
as equivalents, since they have the same
transition temperature of 66 F, whereas
the same steels behave quite differently
when tested with the keyhole notch.
This cannot be too surprising, even
though exceptional, since the test bars*
sample the behavior with two different
stress systems and it is fundamental
that the notch properties of the undeformed metal (cohesive strength and
shear strength or critical shear stress) are
different at the different transition temperatures. This amounts to testing two
different materials of sufficiently different properties to give this difference in
behavior.

temperature, the selection could not be
on a sound basis. Furthermore, this
approach can lead to the selection of too
costly a steel. In case there is no direct
correlation with service (design, strain
rate, and temperature), the procedure
outlined above is available.
The case of selecting a steel which will
stop a running crack is different. While
TABLE I.—TRANSITION TEMPERATURES, DEG FAHR.

Steel
No. 3
V-notch

Keyhole
Difference between
notches

66
14
52

DifferSteel ence BeNo. 6 tween
Steels

66
59
7

0
45

one is still concerned with the presence
of notches and accidental or unavoidable
SUMMARY
initiators of fracture, the problem is
In those cases where design and free- simpler because the notch (the running
dom from dangerous notches are relied fracture) has a specific and constant
upon to avoid starting a brittle fracture geometry, as long as the thickness reand the steel is selected accordingly, mains constant. For this case, laboratory
the brittle transition temperature will, work has developed the V-notch as a

in nearly all cases, select a suitably guide. The indications are that a better
tough steel provided it has been ade- quality steel is needed here because the
quately calibrated against service per- running fracture is a worse hazard than
formance. However, should there be a design and fabrication notches, when
significant difference between the transi- flaws and cracks are eliminated. Ecotion temperature and the low service nomics may step in and play an important
role in steel selection because steel and
5
E. Houdremont, Consultant, Essen, Ger- other costs may be significantly different
for each case.
many, Metal Progress, January, 1955, p. 116.

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DISCUSSION

to ask Mr. Hoyt a question—would he be
brave enough to venture to give some
definition of transition temperature that
may be satisfactory to engineers and
metallurgists? Every time there is a discussion of the impact properties of steel,
the phrase "transition temperature" is
bandied around rather freely, yet we have
such a conglomeration of meanings for
this phrase that very few of us know
what the other means when he uses the
term.
There is an erroneous impression that

may be gained from Mr. Hoyt's phraseology. If I understood him correctly, I
gathered that if a steel were to be used
at a certain low temperature, its use
would be suitable provided its transition
temperature were lower than the service
temperature. Conversely, if its transition
temperature were higher than the service
temperature, its use would not be suitable. This would imply that, whatever
the criterion used to determine transition
temperature, this value should be as
low or lower than the service temperature. I do not believe Mr. Hoyt intended to convey this impression.
Mr. Hoyt's proposal, namely, that
steels should be tested at the minimum
temperature of service by some means so
that differentiation can be made between
the relative toughness of the steels at
that temperature, has real merit. This

MR. S. J. ROSENBERG.1—I should like

would involve changes in the geometry
of the test specimen, with concomitant
changes in severity in the stress system,
until a brittle fracture is obtained at the
temperature in question. If the several
steels considered for use are so evaluated
at the specific temperature involved, it
appears logical to assume that the steel
needing the greatest severity in the stress
system to induce brittleness at that

temperature is the most suitable for use.
MR. A. B. WILDER2 (presented in
written form).—Mr. Hoyt, for many
years, has given much thought and consideration to the toughness of steel; and
in so doing, he has been devoting his
time to a fundamental property, a
property which is just as important
today as it was when he started on this
course of dealing with the toughness of
steel.
The steel producers in general can
provide a steel that is tough. It will be
tough enough to suit most requirements,
but such a steel may be expensive and
require special treatment. The problem
is not necessarily to provide a tough steel
but to provide a steel so that its use will
be justifiable on an economic basis. In
other words, the problem is to develop
tougher steels at a lower cost. There are
tough steels available, but economics
very often do not justify their commercial use. Furthermore, some of these
steels would not be available in the large

1
Metallurgist, U. S. Dept. of Commerce,
National Bureau of Standards, Washington,
D. C.
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2
Chief Metallurgist, National Tube Division, U. S. Steel, William Perm Place, Pittsburgh, Pa.

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8

SYMPOSIUM ON IMPACT TESTING

tonnages that certain applications would
require. For example, a steel utilizing
nickel to provide toughness may be
available in only limited quantities because of Governmental restrictions on
the use of nickel.
With regard to the general subject of
the toughness of steels, I believe that
most steel producers recognize the importance of this problem in their steelmaking processes. There is much work
being conducted in various steelmaking
plants throughout the nation on the
subject. This work has been in progress
for many years. In other words, steel
mill metallurgists are concerned with the
toughness of steel and are doing many
things to try to improve that property;
and if we are going to consider a new
steelmaking process we must evaluate
the property Mr. Hoyt discussed, that is,

the toughness of steel.
Another important consideration in
the development of new steelmaking
processes is the factor of utilizing existing processes and special treatments
available in the various plants. For
example, there are two new steelmaking
plants recently constructed, using the
oxygen-lance method—a plant in Canada
and in the United States. In Europe there
are several plants using this method,
which is often called the L-D process. In
these new processes the toughness characteristics of steel have been given consideration, and in this respect, I would
say the steel industry was traveling in
the right direction with respect to the
factors which are related to the toughness
of steel.
In the matter of crack initiation and
crack propagation, there are two fundamental characteristics involved, and
when you deal with crack initiation the
requirement is less with regard to toughness than with crack propagation. In
other words, tougher steels are required
to stop the propagation of a crack after
it has started than to prevent one from

starting. There has been, and will continue to be, considerable emphasis on
this matter of the crack initiation. Efforts
will continue in an attempt to develop a
steel in which the crack will not initiate.
That is less difficult for the steel maker
than to develop a steel which will stop

the crack, although both of these objectives can be achieved at a cost. In addition to the toughness characteristics of
steel, it is frequently more important to
improve design and require careful
handling during installation in order to
achieve the best results. Very often great
emphasis is placed on the toughness of
steel when other factors are more important.
MR. T. B. REYNOLDS.3—I should like
to ask Mr. Hoyt which type of Charpy
specimen is most used, the V-notch or
the keyhole, and is there a trend toward
one or the other?
I should also like to ask if there are
applications in which one is superior to
the other.
MR. S. L. HOYT (author}.—Mr. Rosenberg asked for a definition of transition
temperature. To me the correct transition temperature for any particular
notched test bar is what I have chosen
to call the match point, because that ties
up definitely with the notch properties
of cohesive strength and critical shear
stress. It is the upper temperature of the
brittle temperature range and is the
only point on the whole transition temperature curve that has precise significance. The match point of a structure in
service is presumably the temperature
at which brittle failure occurs, though
this can also happen at lower temperatures.
Mr. Rosenberg asked a question about
the statement that I made of using a
steel whose transition temperature came

below the service temperature. That is
safe provided the proper test bar is used
3
Inspector, Ingersoll-Rand Co., Phillipsburg,
N. J.

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DISCUSSION ON NOTCHED-BAR TESTS
for determining the transition temperature. I believe the paper shows what is
meant by the "proper" test bar and also
that the transition temperature must be
the temperature of brittle fracture, that
is, the match point.
He also mentioned that testing at the
service temperature means changing the
test specimen. I think that is unavoidable.
As I read various articles that are published from time to time, it seems to me
that that concept is being recognized, at
least for guarding against design notches.
To guard against cracks and running
fractures, a more nearly standard, though
more sharply notched, test bar should
be adequate.
Mr. Reynolds asked which notch is
most used. I am not sure what the
correct answer is, but it is my impression

that it is the V-notch at present. The
keyhole was the most popular one some
years ago but when we began getting
these results on ship plate with a fairly
good correlation between the V-notch
and the behavior of ships, I think that
the V-notch acquired a background, or a
pedigree, that has never been produced
for the keyhole notch.
However, that has to do with fracture
propagation. If one were dealing with
initiation of a fracture and if that had
been the point in the study, it might
have been the keyhole notch.
He also asked which one is superior.
I believe it is the one which best matches
the application, and it might be the Vnotch, it might be the standard keyhole,
or it might be some other.
In the case that I cite in the paper,
neither one was satisfactory, or neither
one was superior. If one were studying
deoxidation practice, for example, it is
not so critical which notch you use. The
main thing there is to use a notch bar.
Mr. Wilder opens his discussion on a
cardinal point—how to produce, or
procure, steel which has adequate tough-

9

ness for a given application and at a cost
that will justify its use on an economic
basis. The problem of steel plate for
merchant ships is now a classic example
and it was to meet the situation that
Mr. Wilder mentions that** I proposed,
in the Committe on Ship Steel, the study
of the effects of manufacturing variables
on the toughness of commercial plate
steel. The results of that project have
issued from time to time as publications
of Battelle Memorial Institute.
Steel melting is one of the controlling
variables and, in this connection, it is
necessary to determine the toughness of
the steel which is produced by a new
process, if the product is to be adequately evaluated. The oxygen lance or
L/D process is an example. It appears, as
Mr. Wilder states, that the steel industry
is traveling in the right direction, yet
there is evidence which indicates that a
still greater improvement may be attained and with no prejudicial cost
burden.
It was especially gratifying to have
Mr. Wilder's comments on crack initiation and crack propagation. There has
been a large amount of investigational
work done on these points, but little has
been published on the practical aspects.
That is why, along with their importance, the latter were dwelt on specifically in the paper. If one limits himself,
in the selection of steel, to one whose

toughness is sufficient to stop a crack
from running, he may well find that
economic considerations preclude the
use of that steel. As Mr. Wilder comments, "it is frequently more important
to improve design and require careful
handling during installation in order to
achieve the best results." An example of
a case of this kind was discussed in the
paper. The problem of applying tonnage
steels, where toughness is a factor, is
more acute and difficult than the problem
of applying specially processed steels.

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STP176-EB/Jan. 1956

TRANSITION BEHAVIOR IN V-NOTCH CHARPY SLOW-BEND TESTS
BY CARL E. HARTBOWER1
SYNOPSIS
V-notch Charpy slow-bend tests (see also Armstrong (I)2) have been
conducted over a range of temperatures, using three commercial structural
steels representing the full range of commercial deoxidation practice, and a
number of carbon-manganese steels containing 0.04 to 0.45 per cent carbon
and 0.43 to 1.05 per cent manganese. The criteria used in evaluating slowbend performance were (1) lateral expansion, (2) fracture appearance, and (3)
temperature. In particular, attention was focused on the deformation, fibrosity, and temperature attending catastrophic crack propagation (sudden
and complete fracture of the test specimen at maximum load).

It was found that considerable plastic deformation occurs in the V-notch
Charpy slow-bend bar even at temperatures resulting in 90 per cent crystallinity and catastrophic crack-propagation. By defining transition temperature
as the highest temperature at which an initiating crack can propagate under
action of the elastic-stress energy alone, that is, sudden and complete fracture
of the test specimen at maximum load, and by noting the deformation occurring in specimens which fractured at maximum load, it was possible to differentiate between the deformation attending the crack initiation and crack
propagation stages of fracture in slow bend.

under investigation in the United States
and Europe. All of the tests are more or
less consistent in rating a given series
of steels in the same order. However,
the choice of performance criteria and
the attendant definitions of transition
temperature have been an ever-present
source of confusion. Attempts to correlate data from different test specimens,
SELECTION or PERFORMANCE CRITERIA or from a single type of specimen but
For the past ten years or more, the based upon different criteria, or upon
relative merits of various laboratory different definitions of transition temtests for notch-toughness have been perature with a single criterion, have led
to anomalies and probably erroneous
1
Chief, Metals Fabrication Branch, Water- conclusions. Stout and McGeady (2)
town
Arsenal Laboratories, Watertown, Mass.
were among the first to bring the transi2
The boldface numbers in parentheses refer
to the list of references appended to this paper, tion-temperature dilemma into focus.
They contended that the choice of test
see p. 22.
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10
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The objective of this investigation was
to evaluate certain performance criteria
and a particular definition of transition
temperature for use in connection with
V-notch Charpy slow-bend tests. The
performance criteria were evaluated on
the basis of their response to selected metallurgical variables.

Copyright© 1956 by ASTM International

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HARTBOWER ON TRANSITION BEHAVIOR
specimen is far less critical for the correlation of test results than is the choice
of criterion used in establishing the
transition temperature.
The selection of the criteria used in
this investigation for evaluating slowbend performance was based upon the
following observations regarding cracking in the V-notch Charpy specimen and
regarding the difference between ductile
and brittle fracture:
1. Crack initiation occurs as a ductile

11

gated by continuous release of the elasticstress field surrounding the crack,
whereas a ductile-fracture crack requires

plastic-deformation work to extend the
crack (4).
In conventional notch-bar impact
testing, results are usually expressed in
terms of (1) the energy absorbed in producing fracture, or (2) the amount of
fibrosity (or crystallinity) in the fracture
surface. In slow-bending, on the other
hand, certain additional information can

FIG. 1.—Typical V-Notch Charpy Slow-Bend Load Deflection Curves.

crack in the root of the notch at the
midpoint of the specimen well before
maximum load is reached; the crack
then grows laterally as the load is increased until it reaches the sides of the
specimen, at which tune a maximum in
the load-deflection curve occurs; and
finally, beyond maximum load, the
crack deepens while extending down the
sides of the specimen (Fig. 1) (3).
2. Brittle fracture may be differentiated from ductile fracture in the manner
in which the initiating crack is propagated; a brittle-fracture crack is propa-

be obtained from the load-deflection
diagram, such as the maximum load
sustained, the deflection to maximum
load or fracture, and from the area under
the load-deflection diagram, the work
done in producing fracture. Raring's
findings (3) suggest that the energy absorbed after-maximum-load is worthy of

special consideration in that it provides
a measure of the work done in propagating a crack through the test specimen.
Thus, if there is zero energy after maximum load, the crack is self-propagating;
that is, the elastic-stress energy stored

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SYMPOSIUM ON IMPACT TESTING

12

in the system is sufficient to drive the
crack through the specimen.
The differentiation between ductile
and brittle fractures suggested by
Orowan appears particularly useful for
the purpose of denning transition tern-

crack is propagated. Thus, when the
load-deflection diagram indicates energy
after maximum load (plastic-deformation work), the elastic-stress energy in
the bar was insufficient to propagate
the crack completely through the speci-

TABLE I.—COMMERCIAL STEELS SUBJECTED TO SUBCRITICAL HEAT
TREATMENT.
CHEMICAL ANALYSIS

Nitrogen, per cent
Material

Fully-killed 1^ in. plate
Semikilled 1 in. plate..
Rimmed % in. plate....

Carbon
per cent

Manganese,
per cent

Silicon,
per cent

Aluminum,
per cent

0.20
0.23
0.19

0.58
0.54
0.35

0.21
0.12
0.01

0.04
0.01
0.01

Soluble
(1:1HC1)

Insoluble

0.006
0.005
0.007

ml
nil
0.003

TENSILE PROPERTIES
(After Normalizing at 1650 F for 1^ hr)
Material

Fully-killed steel.
Semikilled steel. .
Rimmed steel. . . .

Yield Strength,
0.2 per cent
Offset, psi

Tensile
Strength, psi

Elongation in
2 in., per cent

Reduction of
Area, per cent

42 100
39 600
41 200

62 200
64 000
64 000

39.5
38.0
36.5

67.2
63.8
58.0

LABORATORY CARBON-MANGANESE STEELS
Heat Number

Carbon, per cent

Manganese, per cent

ASTM Grain Size

Pearlite, per cent

20701-G
19924-B
20704-K
20705-M
19927-E

0.04
0.09
0.15
0.21
0.45

0.43
0.43
0.49
0.47
0.43

6
6-7
7-8
8
1-3

4.0
10.0
18.0
25.0
60.0

20702-H
20415-S
19925-C

0.04
0.11
0.20

0.74
0.78
0.69

7
8
8

4.0
15.0
25.0

20703-J
20416-T
20412-F
20706-N

0.04
0.10
0.20
0.31

0.98
1.03
0.92
1.05

7
8
7-8
8

4.0
12.0
25.0
40.0

perature. Both types of fracture are
initiated by the occurrence of a crack,
and the presence of an elastic-stress
field in the surrounding regions is necessary for the occurrence of the crack. The
difference, however, between a ductile
and a brittle fracture, as stated above,
lies in the manner in which the initiating

men. At lower temperatures, however,

brittle fracture occurs at maximum load3
3
For sake of brevity throughout this report,
when a brittle-fracture crack propagates suddenly and completely through the specimen at
maximum load (zero slope of the load-deflection
curve), the crack is referred to as self-propagating, and the highest temperature permitting a
self-propagating crack is referred to as the onset
of brittle fracture.

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HARTBOWER ON TRANSITION BEHAVIOR
or on the ascending part of the loaddeflection curve (see Fig. 1). In other
words, at the lower temperatures the
material is embrittled to such an extent
that the elastic-stress energy is sufficient
to propagate the crack. On the basis of
these considerations, the deformation,
fibrosity and temperature attending

13

nese content (1). The latter,4 containing
carbon ranging from 0.04 to 0.45 per
cent and manganese from 0.43 to 1.05
per cent, were prepared as laboratory
heats, deoxidized with silicon and aluminum to simulate commercial fine-grain

practice, forged to f-in. square bar stock,
and normalized from 1700 F. Metallurgi-

FIG. 2.—Relation Between Lateral Deformation and Energy to Fracture.
NOTE.—The intersection of the energy-after maximum load data band (•) with the abscissa
indicates the amount of deformation occurring at the highest temperature producing a self-propagating crack (at lower temperatures fracture would have occurred on the ascending portion of the
load-deflection diagram and the data would have appeared on the abscissa approaching 0.00-in.
deflection).

fracture at maximum load are deemed
less arbitrary as performance criteria
than, for example, a specified level of
fibrosity (50 per cent shear) or a specified
level of energy (15 ft-lb).
Materials:
The steels used in this investigation
were three commercial structural steels
representing the full range of commercial
deoxidation practice (rimmed, semikilled and fully killed), and a series of
12 heats of controlled carbon and manga-

cal and physical property data are listed
in Table I.
Test Method:
The standard V-notch Charpy specimen was used exclusively. Charpy impact data on the 12 steels of varied
carbon and manganese content were
4
Supplied through the courtesy of Messrs.
O. O. Miller and T. N. Armstrong of the Research and Development Division, International
Nickel Co., Inc., New York, N. Y.

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14

SYMPOSIUM ON IMPACT TESTING

obtained from the earlier work of T. N.
Armstrong and W. L. Warner (1).
For purposes of slow-bend testing, the
bars were supported horizontally by a
fixture on the platen of a hydraulic
testing machine and were loaded by a
ram fastened to the fixed head of the
machine. All dimensions of the support-

fixed head and the moving platen of the
testing machine. The energy absorbed to
a specific deflection or to fracture was
calculated from planimeter readings of
the area under the load-deflection curve.
The slow-bend testing, in contradistinction to the case of impact where adiabatic
deformation may occur, was essentially

FIG. 3.—Effect of Aging on the Energy-Deformation Relationship.

ing fixture and loading ram were made

to conform with those specified for the
anvil and striking hammer in the Charpy
impact test. The supporting fixture was
contained in a tank so that the specimens could be tested while totally immersed in a liquid. The slow-bend specimens were loaded at a deflection rate of
0.01 in. per min. The load-deflection diagram was automatically recorded by a
microformer-type deflectometer actuated
by the change hi distance between the

isothermal hi that the rate of loading
was slow and the specimen was completely immersed hi liquid.

TEST RESULTS
Amount of Deformation Attending Brittle
Fracture:
A single plate of commercial fullykilled pearlitic steel, in the as-rolled
condition and containing a variation in
grain size from end to end of the plate,

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HARTBOWER ON TRANSITION BEHAVIOR

15

FIG. 4.—Effect of Carbon and Manganese on the Energy-Deformation Relationship.
NOTE,—The groups containing 0.04 and 0.20 per cent carbon consist of three heats each with
manganese ranging from 0.43 to 0.92 per cent.

was tested in slow bend over a range of
temperatures encompassing the transition from ductile to brittle behavior,
The data as plotted in Fig. 2 indicate

that a simple relationship exists between
energy absorbed and lateral deformation
throughout the range of energy in which
the specimen was completely fractured

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SYMPOSIUM ON IMPACT TESTING

FIG. 5.—Effect of Carbon and Manganese on the Fibrosity-Energy Relationship.
NOTE.—The groups containing 0.04, 0.10 and 0.20 per cent carbon consist of three heats each
with manganese ranging from 0.43 to 1.03 per cent.

FIG. 6.—Effect of Carbon and Manganese on the Fibrosity-Energy Relationship.
NOTE.—Data are for 12 laboratory heats tested in slow bend over a range of temperature encompassing the ductile-to-brittle transition.

and also reveal that a substantial amount
of deformation occurred in the test
specimen, even at temperatures producing a self-propagating crack (sudden
and complete fracture at maximum load).

The latter observation is based upon the
fact that the energy-after-maximum-load

band intersects the abscissa at approximately 0.04 in. (10 per cent) lateral
expansion. Furthermore, it is deduced
that the deformation measured in fractured test specimens which suddenly
and completely separated at maximum
load was prefracture deformation; that

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HARTBOWER ON TRANSITION BEHAVIOR
is, it was the deformation attendant
upon the bending and crack-initiation
stage of the fracture process.
Three commercial pearlitic steels of
fully-killed, semikilled and rimmed deoxidation practice, subjected to a variety
of subcritical heat treatments, were
tested in slow bending over a range of
temperatures encompassing the transition from ductile to brittle behavior.
The data as plotted hi Fig. 3 confirm the
observation that appreciable deformation occurred in the test specimen, even
at temperatures producing brittle fracture, and show that the amount of deformation is affected by metallurgical
variables introduced by deoxidation
practice and subcritical heat treatment.
Likewise, in the case of the laboratory
heats of carbon-manganese steel (Fig. 4),

an appreciable amount of deformation
occurred in specimens tested at temperatures producing brittle fracture. Note
that as the carbon (pearlite) content
increased, the deformation corresponding to the case of a self-propagating
crack decreased from approximately 15
per cent (with 0.04 per cent carbon) to
somewhat less than 5 per cent (with 0.45
per cent carbon).5
Amount of Fibrosity Attending Brittle
Fracture:
The laboratory heats containing varying amounts of carbon and manganese
were examined as to the relationship
between per cent fibrosity and energy
after maximum load (work required for
crack propagation). The steels as plotted
in Fig. 5 are grouped according to carbon
content; the groups containing 0.04, 0.10
and 0.20 per cent carbon consist of three
heats each, with magnanese ranging
from 0.43 to 1.03 per cent. The data
8
In the case of the 0.04 and 0.20 carbon plots,
each contains data from three steels with manganese content ranging from 0.43 to 0.98 per
cent. These data when plotted separately (according to manganese content) showed little or
no separation.

17

indicate that the amount of fibrosity
attending the onset of brittle fracture

(highest temperature permitting a selfpropagating crack) consistently fell
within the range of 0 to 20 per cent for
all carbon contents investigated. The
average for all steels was 10 per cent
fibrosity (90 per cent crystallmity).
Thus, the amount of fibrosity attending
the onset of brittle fracture was low
and relatively unaffected by carbon
content.
Relationship Between Fibrosity and Total
Energy:
For a more complete understanding
of the two performance criteria, the
relationship between per cent fibrosity
and total energy was plotted for several
of the carbon-manganese heats (Fig. 6).
Again, the heats were grouped according
to carbon content (seven heats fell into
the group containing 0.04 to 0.15 per
cent carbon, and although manganese in
this group ranged from 0.43 to 1.03 per
cent, separate plotting revealed no distinction between heats). The data as
plotted in Fig. 6 indicate that: (1) the
work required to produce fracture decreased with increasing crystallmity,
(2) the rate at which the work decreased
with increasing crystallmity was a
function of carbon (pearlite) content,
and (3) the maximum amount of work
attending 90 per cent crystallinity
varied from approximately 10 ft-lb for

0.45 per cent carbon to 85 ft-lb for
0.04 per cent carbon.
Ejfect of Carbon and Manganese on the
Shape of Transition Curve:
Total energy as measured by planimeter from the slow-bend load-deflection
diagram was plotted against testing
temperature and, for purposes of comparison, the data obtained from impact
tests by Warner and Armstrong (l) were
replotted on the same coordinate system.
The five heats containing carbon ranging

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SYMPOSIUM ON IMPACT TESTING

FIG. 7.—Effect of Carbon on the Energy-Temperature Relationship in Slow Bend and Impact.
NOTE.—The steels shown contain essentially constant manganese (0.43 to 0.49 per cent).

FIG. 8.—Effect of Carbon on the Fibrosity-Temperature Relationship in Slow Bend and Impact.
NOTE.—The steels shown contain essentially constant manganese (0.43 to 0.49 per cent).
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