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MEMORANDUM
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NUM6ERl
ICATEOORYI
FATIGUE:
A
COMPLEX SUBJECT
-
SOME
SIMPLE
APPROXIMATIONS
Microfiche
(MF)
,
by
S.
S.
Manson
Lewis Research Center
Cleveland, Ohio
WILLIAM
M.
MURRAY LECTURE
Presented
to
Society
for
Emerimental Stress
Analysis
Cleveland, Ohio, October
30,
1964
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C.
-
1965
FATIGUE:
A COMPLEX SUBJECT
-
SOME SIMPLE APPROXIMATIONS
by
S.
S.
Manson
Lewis Research Center
Cleveland, Ohio
WILLIAM M. MURRAY LECTURE
.
Presented to
the
Society for Experimental
Stress
Analysis
Cleveland, Ohio, October
30,
1964
NATIONAL AERONAUTICS
AND
SPACE ADMINISTRATION
FOREWORD
It
was
my privilege to serve
on
the Executive Committee of the
Society for Experimental Stress Analysis in
1951
when this lectureship
was
first
inaugurated. Normally
our
concern
was
largely with financial
matters, but
at
this meeting our subject of discussion
was
much more
pleasureable
-
how could
we
be of greater service to the membership of
the Society and to the technical community
at
large?
One of the members
of the committee suggested that
it
was about time
-
we
were then
8
years
old
-
to institute an honorary lectureship within the Society.
This
sounded like
a
very good idea, and we were about to embark on
a
dis-
cussion
as
to how
it
would be designated.
Frankly my thoughts turned
in the direction of some elderly hero of the past in the field of stress
analysis.
I
did not think
at
all
along the lines of one of the other mem-
bers who
sat
next to me and
said,
"How
about
Bill
Murray?".
Bill
was
not
in the
room
at
the time. After the suggestion
was
made, however,
it
seemed like the only possible idea.
I
wondered how
I
could ever have
thought in any direction other than that.
Bill
was
a
founder,
he
was
our
first
president,
he
was
the Executive Secretary, and
our
Treasurer.
Between meetings he
was
the entire Society and did
all
of the work, in-
cluding editing of the Journal.
He
did
this on donated time without
remuneration.
So
the suggestion not only made sense, but
it
really
was
the only right thing to do.
By
the time
Bill
came back, there
was
no
need for discussion.
I
did
not need to be convinced and neither did
anyone else. The decision
was
unanimous;
it
was
to be the
William
M.
Murray Lecture.
We asked
Bill
if
he would give the
first
lecture,
and,
i
ii
of
course, he did.
been followed ever since. The twelve Murray lectures that have been
given in the ensuing years have
all
been
a
true credit to the Society.
It
is
indeed a privilege to take a place among those honoring
Bill,
and
it
is
my hope that the lecture that
I
shall present to you
will
in
small
measure, at least, follow the high standards that have already been set.
In
so
doing he set
a
standard
of
excellence that has
iv
.
TABU
OF
CONTENTS
FORENARD
..............................
iii
INTRODUCTION
............................
SOME
RECENT
EXPERIMENTAL
TOOLS
AND
TECHNIQUES
...........
1
3
PHENOMENOLOGICAL
BEHAVIOR
IN
STRAIN
CYCLING
..........
Strain Cycling Concepts
...................
Prediction of Axial Fatigue Life from Tensile
Cetta
.....
Method of universal slopes
.................
Comparison of Prediction Methods
...............
Alternate Relation for Predicting Axial Fatigue
Life
in
Terms
of Endurance
Limit
......................
Four-point correlation method
...............
..
8
..
8
.
.
12
.
.
12
.
.
16
. .
17
.
.
19
EFFECT
OF
YIELD
STRESS
AND
NOTCH
SENSITIVITY
ON
FATIGUE
LIFE
IN
STRAIN
CYCLING
.........................
21
CONSIDERATION OF
UNIVERSAL
SLOPE
FOR PLASTIC STRAIN
LINE
.....
27
CRACK
PROPAGATION
AND
ITS
RELATION
TO
THX
POWER
LAW
FOR
CYCLIC
LIFE
............................
29
CUMULATIVEFATIGUE
DAMAGE
.....................
36
37
Aspects Relating to Crack Propagation
..............
41
Cyclic Hardening and Softening
..................
APPLICATIONS
INVOLVING
STRAIN
CYCLING
DATA
.............
47
47
Relation Between Axial and Bending Fatigue
............
Rule of
Thumb
Relating Strain Range
to
Cyclic Life
........
53
FUNDAMENTAL
ASPECTS OF FATIGUE
...................
54
Cyclic Strain Hardening and Softening
..............
54
Microstructural Events in Fatigue
................
56
Development of Microcracks
....................
59
Stage
I1
Cracking
........................
63
FinalFracture
..........................
67
ACKN0WL;EDGMENT
...........................
67
REFERENCES
.............................
68