WADC TECHNICAL REPORT 52-307, Part II
FATIGUE PROPERTIES OF ALUMINUM ALLOYS
AT VARIOUS DIRECT STRESS RATIOS
Part II - Extruded Alloys
B. J. LAZANAND
A. A. BLATHERWICK
DECEMBER 1952
Statement A
4. Approved for Public Release
WRIGHT AIR DEVELOPMENT CENTER
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WADC TECHNICAL REPORT 52-307, Part II
FATIGUE PROPERTIES OF ALUMINUM ALLOYS
AT VARIOUS DIRECT-STRESS RATIOS
Part II - Extruded Alloys
B. J. LAZAN AND A. A. BLATHERWICK
UNIVERSITY OF MINNESOTA
Materials Laboratory
Contract No. AF33(038)-20840
RDO No. R 614 - 16
Wright Air Development Center
Air Research and Development Command
United States Air Force
Wright-Patterson Air Force Base, Ohio
FOREWORD
This report was prepared by the University of Minnesota under
Contract No. AF33(038)-20840 with the Wright Air Development Center,
Wright-Patterson Air Force Base, Ohio, identified by the Expenditure
order No. R614-16. It was administered under the direction of the
Materials Laboratory, Wright Air Development Center, with Mr.
W. J. Trapp acting as project engineer.
In addition to the authors, the following personnel of the Univer-
sity of Minnesota contributed in this work: F. W. DeMoney, metallurgist,
and P. M. Kemmer, technician.
WADC 52-307, Part II ii
ABSTRACT
Axial-stress fatigue tests were performed at various stress ratios
on extruded aluminum alloys 14S-T6, 24S-T4, and 75S-T6 using one un-
notched and one notched type of round specimen. The data are presented
in the form of S-N curves and stress-range diagrams to analyze the effect
of: (a) stress ratio, ranging from static tension to reversed axial stress,
(b) stress magnitudes which cause failure in the range from 103 to 107
cycles, and (c) stress concentration resulting from a circumferential
V-notch. The notch-sensitivity data are further analyzed by diagrams
which display the importance of stress ratio, stress level, and life on
fatigue strength reduction. The fatigue properties of the three extrudedalloys are compared both with each other and with rolled aluminum alloys.
PUBLICATION REVIEW
Manuscript copy of this report has been reviewed and found satis-
factory for publication,
FOR THE COMMANDING GENERAL:
M. R. WHITMOREfor M. E. SORTE
Colonel, USAFChief, Materials LaboratoryDirectorate of Research
WADC TR 52-307, Part II iii
TABLE OF CONTENTS
Sections Page
I. Introduction 1II. Test Program 1
III. Materials 23. 1 Specifications 23.2 Processing 23.3 Chemical Analysis 23.4 Metallographic Structure 3
IV. Test Specimens 34. 1 Design of Specimens 34.2 Preparation of Specimens 3
V. Testing Equipment 45. 1 Fatigue Testing Machines 45.2 Calibration 4
VI. Results and Discussion 46. 1 Static Tensile and Hardness Properties 46.2 Fatigue Properties of 14S-T6 56.3 Fatigue Properties of 24S-T4 86.4 Fatigue Properties of 75S-T6 8
VII. Comparison of Properties of the Three Alloys 107, 1 Fatigue Strength 107.2 Notch Sensitivity 10
VIII. Summary and Conclusions 11-Bibliography 12
Tables
I. Static Properties of 14S-T6 13II. Static Properties of 24 -T4 13
III. Static Properties of 75S-T6 14IV. Fatigue Data on 14S-T6 15V. Fatigue Data on 24S-T4 16
VI. Fatigue Data on 75S-T6 17
Figures
1. Photomicrographs of Test Materials 182. Drawing of Test Specimens -193. S-N Curves for Unnotched 14S-T6 -204. S-N Curves for Notched 14S-T6 205. Stress-Range Diagrams for Unnotched 14S-T6 216. Stress-Range Diagrams for Notched 14S-T6 21
WADC TR 52-307, Part II iv
Figures Page
7. Notch Sensitivity Chart of Kf vs. S and S for 14S-T6 228. Notch Sensitivity Chart of Kf vs. Ilfe andnTtress Ratio
for 14S-T6 229. S-N Curves for Unnotched 24S-T4 23
10. S-N Curves for Notched 24S-T4 2311. Stress-Range Diagrams for Unnotched 24S-T4 2412. Stress-Range Diagrams for Notched 24S-T4 2413. Notch-Sensitivity Chart of Kf vs. S and S for 24S-T4 2514. Notch-Sensitivity Chart of Kf vs. i1fe andcFStress Ratio
for 24S-T4 2515. S-N Curves for Unnotched 75S-T6 2616. S-N Curves for Notched 75S-T6 2617. Stress-Range Diagrams for Unnotched 75S-T6 2718. Stress-Range Diagrams for Notched 75S-T6 2719. Notch-Sensitivity Chart of Kf vs. S and S for 75S-T6 2820. Notch-Sensitivity Chart of Kf vs. Ilfe andmStress Ratio
for 75S-T6 2821. Composite Stress-Range Diagrams for 14S-T6, 24S-T4,
and 75S-T6 29
WADC TR 52-307, Part II v
FATIGUE PROPERTIES OF ALUMINUM ALLOYS
AT VARIOUS DIRECT-STRESS RATIOS
PART II - EXTRUDED ALLOYS
I. INTRODUCTION
The justification for additional work in the fatigue and notch
sensitivity properties of aluminum alloys was discussed in Part I of
this report issued recently. The data on rolled aluminum alloys are
presented in Part I and the results of the tests on extruded alloys are
given in this, the second part of the report. This extension of the
original program to include extruded alloys is justifiable because of
the increasing use of extruded parts in aircraft structures as well as
other engineering applications.
II. TEST PROGRAM
All fatigue tests in this work were conducted under axial (tensile
or compressive) stress at room temperature. In order to study the effect
of range of stress and to compare results with those of rolled aluminum,
stress ratios A (ratio of alternating stress to mean stress) of 0, 0. 15, 0. 89,
and infinity were used (1). * As the work progressed, it became evident that
the extruded alloys exhibited the same trends as the rolled materials and
consequently only about four points were needed to establish each S-N curve
sufficiently for comparison purposes.
Two of the specimen types used in the rolled-alloys program were
employed for notch sensitivity studies included in this report. The first
was a single-filleted unnotched specimen and the second was notched having
a theoretical stress concentration factor Kt of 3.4. These specimens are
described in more detail in Section IV.
.Numbers refer to references in the Bibliography.
WADC TR 52-307, Part II - 1 -
III. MATERIALS
3. 1 Specifications for Test Materials
The three aluminum alloys used in this program are: 14S-T6
(spec. QQ-A-266), 24S-T4 (spec. QQ-A-268), and 75S-T6 (spec.
QQ-A-282), all in extruded bar stock form.
3.2 Processing
Each of the three materials was received in the form of
1 1/4 in. extruded bars 10 ft-, long as furnished by the Aluminum Com-
pany of America.
All bars of each material were extruded from a single cast ingot,
although to facilitate handling the ingot was cut into three pieces. The
bars were extruded by standard practice through a 2-hole 1 1/4 in. die.
Bars were labeled to indicate the die through which they were extruded
and the bar position in the- original cast ingot. When the bars were cut
into blanks for specimens, the position in the bar was recorded, so that
if serious scatte-i were observed in the data, the effect of possible in-
homogeneity of the material with reference to location in the ingot might
be evaluated.
The materials were solution heat treated by Alcoa following
extrusion. For 14S-T6 the treatment was 930' F followed by artificial
aging at 3200 F for 18 hours. The 24S-T4 was solution heat treated at
9200 F, while 75S-T6 was treated at 870' F and then artificially aged
for 24 hours at 2 5 0 ' F. All bars were slightly stretched after heat
treatment.
3. 3 Chemical Analysis
Chemical composition (percent) as furnished by Alcoa is as
follows:
Cu Fe Si Mn Mg Zn Cr Ti
14S-T6 4.46 0.43 0.95 0.80 0.44 0.07 0.00 0.00
24S-T4 4.30 0.22 0.14 0.61 1.54 0.01 0.01 0.01
75S-T6 1.57 0.20 0.12 0.02 2.46 5.63 0.23 0.02
This attention to location details was later found to be unnecessarysince the test data were reasonably uniform and the association of dis-crepancies in results with bar location was unnecessary.
WADC TR 52-307, Part II - 2 -
The composition of the extruded alloys indicated above may be
considered equivalent to the composition of the rolled alloys given in
Part I.
3.4 Metallographic Structure
The metallographic structure of the three materials is shown in
the photomicrographs of Fig. 1. The structure appears to be normal
for extruded alloys. The characteristic elongated grains are prominent
in the longitudinal sections, while the transverse sections reveal rather
uniform grain size.
IV. TEST SPECIMENS
4. 1 Design of Specimens
The two types of specimens shown in Fig. 2 were used, one
being unnotched while the second was notched to produce a stress
concentration. Both specimens have a test-section diameter of 0. 400 in.
The filleted specimen has insignificant stress concentration and thus Kt
is 1.0 for the unnotched specimens. The notched specimen has a 600
V-notch with a root radius of 0. 01 in. with a theoretical stress concentra-
tion factor determined from Neuber's Charts (2) of 3.4.
Both of these specimen types were also used in the rolled alloy
program discussed in Part I.
4. 2 Preparation of Specimens
All fatigue specimens were machined and polished by the John
Stulen Company of Gibsonia, Pennsylvania. Special procedures were
followed to insure uniformity of surfaces, to avoid circumferential
scratches, and to reduce to a minimum the residual stresses due to
machining. Details on the procedures employed are described in (1).
WADC TR 52-307, Part II - 3 -
V. TESTING EQUIPMENT
5.1 Fatigue Testing Machines
All fatigue tests were conducted in axial-stress machines capable
of imposing on the specimen any combination of forces up to + 5000 pounds
alternating force and 9000 pounds static tensile force. The alternating
force is provided by an eccentric driven by a 3600 rpm synchronous motor.
The static force is applied by helical springs, and provision is made to
automatically maintain this force if the specimen elongates during a test.
Specially designed gripping devices are used to eliminate as far as possible
bending stresses due to gripping the specimen. A detailed description of
test equipment is given in (1).
5. 2 Calibration
Considerable care was taken to insure that the stresses imposed
during the tests were accurately controlled. -Machines were originally
calibrated by three independent methods and spot checks were made through-
out the test program. Stresses were thus controlled to within + 5 percent
at all times.
VI. RESULTS AND DISCUSSION
6. 1 Static Tensile and Hardness Properties
In order to evaluate the uniformity of each of the three test materials
and to compare the properties with accepted values, static tensile tests
and hardness tests were performed. Specimens were prepared from blanks
taken from one end of each 10 ft bar, and standard ASTM tests were run
to determine tensile strength, yield strength, modulus of elasticity, and
percent elongation. These values, together with Rockwell A hardness
numbers, are given in Tables 1, 11, and III. These results compare quite
favorably with values given by Alcoa (3) for extruded alloys, although the
tensile and yield strengths are 5to 10 percent higher than those found in (4).
WADC TR 52-307., Part II - 4
The strengths are significantly higher (9 to 20 percent) than for rolled
alloys previously tested (1).
Tensile tests were also performed on fatigue type specimens, and
these results are included in Tables I, II, and III. As in the case of the
rolled alloys, the unnotched specimens exhibited slightly higher tensile
strengths than the ASTM straight specimens and the notched specimens of
14S-T6 and 75S-T6 exhibited significantly higher strengths. The notched
specimens of 24S-T4 had tensile strengths approximately the same as those
of the straight specimen. This behavior corresponds with that observed
for rolled 24S-T4.
In addition to the hardness data given in the tables, hardness surveys
were made to determine the uniformity of specimens taken from different
locations in the ingot. These surveys revealed good uniformity of the
materials, and there was no significant variation in either longitudinal or
transverse sections of individual specimens.
6.2 Fatigue Properties of 14S-T6
6. 2. 1 S-N Diagrams. The data obtained on fatigue strength of un-
notched and notched specimens of 14S-T6 are given in Table IV and are
plotted in the form of S-N curves in Figs. 3 and 4. In these diagrams the
logarithm of the crest stress, Sc, is plotted against the logarithm of N, the
number of cycles to failure. Three curves are plotted, one for each of the
three stress ratios used (A = 0. 15, 0. 89, and w), as indicated by the point
and line code. Because of the logarithmic scales, a fixed distance represents
a constant percentage at any ordinate and for reference a 10 percent spread
is indicated at the lower left of the diagram.
As would be expected, the curve for A - oo is the lowest while that
for A = 0. 15 is highest for both the notched and unnotched specimens. It
may be observed, also, that the curves for higher stress ratio have a some-
what steeper slope than those for which the percentage of alternating stress
is less. Although the curves become quite flat at the long-life end, there is
no certainty that they have a horizontal asymptote. It is therefore not possi-
ble with these limited data to establish a definite fatigue limit.
WADC TR 52-307, Part II - 5-
These curves have a pattern quite similar to those for rolled 14S-T6
(1). A comparison of the two materials can better be seen, however, in the
diagrams described below.
6. 2. 2 Stress-Range Diagrams. The data from Figs. 3 and 4 are
replotted in Figs. 5 and 6 in a coordinate system of alternating versus mean
stress to better reveal the effect of range of stress on fatigue life.... The
curves show. combinations of alternating and mean stress resulting in a given4 5 7life. In these diagrams, constant-life curves for 10 , 10 , and 10 cycles
are shown, and as the code indicates, the solid curves are for extruded
14S-T6 while the dashed curves are for the rolled alloy (1). The static
ultimate strength for extruded 14S-T6 is indicated by the S designationU.on the horizontal axis, and the dashed line extending from this point at a450 angle indicates the cocnbinations of alternating stress Sa and mean-stress
Sm whose sum equals the ultimate strength. The radial lines through the
origin indicate the stress corhbinations for a given stress ratio. the vertical
axis representing A = oo while the horizontal axis is A = 0.
In Fig. 5, the curves for unnotched specimens of both the extrudedand rolled alloys are shown. Here the definite similarity in behavior is
evident and the fatigue strengths of the two materials may be readily compared.
The fatigue strengths of the extruded alloy, like the static strengths, are
slightly higher in all cases. The shape of the curve for 107 cycles is quitesignificant. Because it is quite flat, it is evident that the relative amount
of alternating stress is more important in determining fatigue life than is
the mean stress.
This observation becomes even more noticeable in the case of notched
specimens diagrammed in Fig-. 6 where all the curves are very flat. In this
case, also, it may be seen that the two materials have very similar behavior
and that the extruded fatigue strength is generally somewhat higher than that
of the rolled. A comparison of Figs. 5 and 6 shows a marked difference in
the fatigue strengths of notched and unnotched specimens due to stress con-
centration. This effect is further analyzed in the diagrams described below.
6. 2. 3 Notch Sensitivity. In order to analyze the harmful effect of a
notch or stress raiser, the fatigue strength reduction factor, Kf, is defined
as the ratio of the stress in an unnotched specimen to the corresponding stress
WADC TR 52-307, Part II - 6 -
in a notched specimen at a given life. * In Fig. 7 the variation of Kf with
stress level and with stress ratio is shown by means of contours of constant
Kf plotted on a grid of alternating versus mean stress in the unnotched
specimen. These curves were developed by first plotting "profile" curves
(not shown) of Kf versus either Sa or Sm, and then the desired Kf values
were located on the stress-ratio lines of Fig. 7. These points were joined
to form the contour curves shown. Extrapolated portions of the curves
are dashed.
A study of Fig. 7 reveals several pertinent facts regarding the
strength-reduction factor. It is of course obvious that Kf is not constant,but varies with the stress level and with stress ratio. The largest observed
values of Kf occur at A = oo and the least values are found at A = 0.15. At
all stress ratios, Kf decreases as the stress is increased. This should be
expected, since at high stress (and corresponding short life) the fatigue
strengths approach the static ultimate strength which is higher for the notched
specimen. In fact, at A = 0 (static test) the strength reduction factorunnotched Su) reduces to 0.91, a point that is shown on the horizontal axis of
notched Suthe figure. Other features of this type of figure are discussed in Part I.
In order to observe further the stress concentration trends, thevariation in Kf is shown in Fig. 8 as a function of life and stress ratio R. **
The corresponding values of A are shown in the scale at the right. These
contour curves of Kf were plotted by using "profiles" of Kf versus N and Kf
versus R. The selected values of Kf were thus located and the contour curves
were drawn.
It is evident from Fig. 8 that Kf varies with both life and stress ratio.
in the lower half of the diagram (essentially vertical contour lines) Kf if
affected more by life and stress ratio is relatively unimportant, whereas in
the upper region (essentially horizontal contour lines) stress ratio is the more
significant factor. In this figure it is quite clear that the strength reductionfactor decreases as the percentage of alternating stress is reduced. This
type of plot also shows that the highest value of Kf occurs at A = no and at a long life.
In an analysis based on fixed stress ratios, the ratios of crest stress,alternating stress, and mean stress are all the same.
• R is the ratio of minimum stress in a cycle to the crest stress and isused instead of A since the range in R values from -1 to +1 is easier to dia-gram thail the range of A values from 0 to co.
WADC TR 52-307, Part II - 7-
The general pattern and behavior of Kf for extruded 14S-T6 observed
in Figs. 7 and 8 is very similar to that of rolled 14S-T6 (1).
6.3 Fatigue Properties of 24S-T4
6.3. 1 S-N Diagrams. In Figs. 9 and 10 are shown the S-N curves
for unnotched and notched specimens respectively of 24S-T4. The curve forA = 0. 15 for unnotched specimens (Fig. 9) is extremely flat. One test run at
a crest stress of 90, 000 psi lasted only approximately 300 cycles, while
another at a stress only 4000 psi less ran for over 5 million cycles. It
will be noted that two points appear in the diagram at a stress slightlyin excess of the static ultimate strength of the specimen. The significance
of this observation, however, is questionable because of the accuracy of
imposed stresses.
6. 3. 2 Stress-Range Diagrams. The stress-range data for unnotched
and notched specimens of 24S-T4 are diagramed in Figs. 11 and 12. Here
again, it is apparent that the rolled and extruded materials follow-generally
the same pattern, except that the fatigue strengths of the extruded material
are from 7 to 15 percent higher as is the static strength. It should be notedthat, as in the case of other materials, the notched stress-range curves are
very flat.
6. 3. 3 Notch Sensitivity. Figure 13 shows the variation in Kf with,stress ratio and magnitude. As for 14S-T6, Kf becomes larger as the stressdecreases reaching a maximum value of 2. 6 at A = 0. 89 and co. The variation
of Kf with stress ratio and life is shown in Fig. 14. Both factors generally
affect the value of KfS but in the lower half of the diagram N seems to be
more significant while stress ratio predominates in the upper half.
The behavior of this material as regards notch sensitivity is very
similar to that of the rolled 24S-T4 (1).
6.4 Fatigue Properties of 75S-T6
6.4.1 S-N Diagrams. Figures 15 and 16 are the S-N curves for75S-T6. These curves display practically the same trends as those for
14S-T6 and 24S-T4, the unnotched specimens having flatter curves and,
of course, higher fatigue strengths. Here again, there is no conclusive
WADC TR 52-307, Part II - 8 -
evidence of the existence of an endurance limit; in fact, within the range ofdata procured, the curves continue to fall after 10 million cycles.
6.4.2 Stress-Range Diagrams. In Figs. 17 and 18 the stress-range
curves for unnotclhed and notched 75S-T6 are shown. It will be noticed that,
although the general trends are the same, the fatigue strength of the extruded
alloy is in some cases as much as 95 percent higher than that of rolled 75S-T6.
This is in line with conclusions reached in the report on rolled alloys (1) that
the fatigue strength of the rolled 75S-T6 tested in that program was abnormally
low. It is believed that the fatigue strength of this extruded 75S-T6 is more
near the a~rerage value for this material.
In the case of notched specimens, the difference in fatigue strengths
of extruded and rolled materials is not as great, although the strength of the
extruded material is significantly higher. The extreme flatness of the curves
is again very noticeable.
6.4.3 Notch Sensitivity. The behavior of Kf for 75S-T6 is shown in
Figs. 19 and 20. In Fig. 19 the values of Kf are uncertain over much of the
area, so the contours are dashed in those regions. The data show a region
of maximum Kf at A = 0. 89 and at moderate stress. For stresses eithergreater or less the value of Kf becomes less, and Kf decreases at A = co and
A = 0.15.
Since the S-N curves from which the Kf values were taken may be in
error by approximately + 5 percent due to scatter in the data, the values ofKf may be off by 10 percent (quotient of two factors whose reliability is
+ 5 percent). It is therefore quite possible that this diagram does not represent
the exact behavior of Kf for this material, although this shape fits the dataquite closely. It is also quite similar to the diagram for rolled 75S-T6 (1)
except that Kf values are somewhat larger than those for the rolled material.
In Fig. 20 the "peak" region occurs at stress ratio A of about 1.4 and
a life of 105 cycles. Again, the exact variation of Kf may not be as indicated,
but certainly Kf decreases as A is reduced and it is dependent upon life.
WADC TR 52-307, Part II - 9 -
VII. COMPARISON OF PROPERTIES OF THE THREE ALLOYS
7. 1 Fatigue Strength
A composite stress-range diagram showing the fatigue strengths of
the three extruded alloys is given in Fig. 21. In Fig. 21a the curves for
unnotched specimens show 75S-T6 to have the highest strength at 104 cycles
with 24$-T4 next and 14S-T6 having the lowest strength. However, at 10 7
cycles the strength of the three materials is practically the same, although
75S-T6 is somewhat stronger in the low stress-ratio region, while 14S-T6
is a little higher near A = co.
In the comparison of notched specimens, Fig. 21b, there is rela-
tively little difference in the fatigue strength of the three materials at
either 104 or 107 cycles. The curves for 104 cycles again show 75S-T6
to be stronger at low stress ratio, but in 'this case, 24S-T4 is slightly
stronger under reversed stress. These slight differences in strength are
not sufficient to indicate a superiority of one material over the other,
especially when scatter in the data is considered. However, it seems
evident that 75S-T6, because of its higher static strength and higher fatigue
strength at low stress ratio, does have significantly higher strength under
loads having relatively low alternating stress.
7.2 Notch Sensitivity
A comparison of the notch sensitivity curves for the three materials
reveals a very definite similarity between the characteristics of 14S-T6
and 24S-T4 both in magnitude and manner of variation of Kf with stress,
stress ratio, and life. The curves for 75S-T6, however, display a dif-
ferent pattern of variation. Where 14S-T6 and 24S-T4 have maximum
values at A = oo and at low stress, 75S-T6 has its maximum at A = 1.4
and at a higher stress. Since the- differ-ences involved are relatively small,
it can not be stated with certainty whether they are due to inherent charac-
teristics of the materials or due to scatter in the data. In general, the
range of values of Kf is about the same for the three materials.
WADC TR 52-307, Part II - 10 -
VIII. SUMMARY AND CONCLUSIONS
In order to compare the fatigue properties of extruded aluminum
alloys 14S-T6, 24S-T4, and 75S-T6 with those of rolled alloys (1), a series
of axial stress fatigue tests were performed. To analyze the effect of range
of stress, tests were conducted under stress ratios, A, of 0. 15, 0. 89, and
oo. To study the effect of stress concentration, both unnotched and notched
type specimens were used. Static tension and hardness tests were also per-
formed for comparison of the test materials with generally accepted standards.
The results for a given material were presented as S-N curves, one
for each stress ratio and specimen type. A comparison of the stress-ratio
curves provided data for analysis of the effect of various combinations of
alternating and mean stress, while a comparison of the two corresponding
curves for specimen types supplied notch-sensitivity data.
These latter analyses were facilitated by the use of stress-range
diagrams and notch-sensitivity curves. In the stress-range diagrams,
curves of constant life were plotted in a coordinate system of alternating
stress versus mean stress. Two types of notch-sensitivity charts were
used. In the first type, curves of constant Kf (fatigue strength-reduction
factor) were plotted as contours in a field of alternating versus mean stress
in the unnotched specimen. The second type showed Kf contours within
a stress-ratio versus cycles-to-failure coordinate system.
The following conclusions are based on the results obtained in
this work:
(a) The static ultimate strengths of the three extruded alloys are
slightly higher than those of rolled materials.4 As in the case of
rolled aluminum, the static tensile strengths of notched extruded
14S-T6 and 75S-T6 are about 10 percent higher than those of un-
notched specimens, while the tensile strength bf 24S-T4 is about
the same for notched and unnotched specimens.
(b) The fatigue strengths of both noadched and unnotched specimens
of extruded 14S-T6 and 24S-T4 are slightly higher at any life
than those of rolled alloys.
(c) The fatigue strength of notched and unnotched extruded 75S-T6
is significantly higher than that found for rolled 75S-T6.
WADC TR 52-307, Part II - 11 -
However, this marked difference (as much as 95 percent for un-
notched specimens) is undoubtedly due to the fact that the fatigue
strengths for rolled 75S-T6 (1) were abnormally low.
(d) The fatigue strengths of unnotched and notched extruded alloys
14S-T6, 24S-T4, and 75S-T6 are practically the same at long life
(ten million cycles or more), except that 75S-T6 is slightly stronger
at low stress ratios. Unnotched 75S-T6 is somewhat stronger during
short-life fatigue.
(e) The notch-sensitivity properties of the three extruded alloys are
about the same as those of rolled materials. The strength reduction
factor, Kf, varies with stress ratio and stress level (or life) and
is maximum for 14S-T6 and 24S-T4 at A = co and at low stress,
For 75S-T6, Kf is maximum at A = 1.4 and at medium stress level.
The maximum value of Kf for the three alloys is about 2. 8 for a
notch whose theoretical stress-concentration factor is 3.4.
(f) The over-all fatigue behavior of extruded 14S-T6, 24S-T4, and
75S-T6 may be considered the same as that of rolled alloys.
BIBLIOGRAPHY
1. B. J. Lazan and A. A. Blatherwick, "Fatigue Properties of Unnotchedand Notched Aluminum Alloys at Various Direct Stress Ratios" WADCTechnical-Report, 52-307, Part I, December, 1952.
2. H. Neuber, "Theory of Notch Stresses" Edwards Brothers, Ann Arbor,1946.
3. "Alcoa Aluminum and Its Alloys, " The Aluminum Company of Americaý,1950.
4. E. C. Hartman, M. Holt, and I. D. Eaton, "Static and FatigueStrengths of High-Strength Aluminum-Alloy Bolted Joints, " NACA TN2276, February, 1951.
WADC TR 52-307, Part II - 12 -
TABLE I. STATIC PROPERTIES OF 14S-T6EXTRUDED ALUMINUM ALLOY
Specimen Hardness Mod. E Tensile 2% OffsetNo. and R 6 Stren th Yield Str.
Type A 10 PSI PSI PSI Elong.
Q 1701 AE* 47.7 10.6 79,065 67,400 11%/2"Q 1702 AE* 47.6 10.3 77,176 70,400 11%/2"Q 1703 AE* 48.3 11.7 78,270 73,300 11%/2"Q 1704 AE* 48.1 10.3 78,323 68,200 11%/2"Q 1705 AE* 48.6 11.2 78,700 73,000 11%/2"Average* 48.1 10.8 78,307 70,460 11%/2"
Q 1711 V 79,520 .086"Q 1725 V 78,185 .092"Average for Type V Specimens (Kt = 1.0) 78,853 .089"
Q 1748 X 87,025 .021"Q 1762 X 86,032 .017"Average for Type X Specimens (Kt = 3.4) 86,529 .019"
TABLE II. STATIC PROPERTIES OF 24S-T4EXTRUDED ALUMIMUM ALLOY
Specimen Hardness Mod. E Tensile .2% OffsetNo. and R M Strength Yield Str.Type RA 106 PSI PSI PSI Elong.
P 1765 AE* 49.1 9.7 84,604 66,009 11. 5%/2"P 1766 AE* 49.6 10.4 85,213 65,564 11. 5%/2"P 1767 AE* 49.5 10.6 85,032 64,888 11. 0%/2"P 1768 AE* 49.8 10.2 85,832 66,028 ii. 0%/2"P 1769 AE* 49.3 10.0 84,873 65,901 10. 5%/2"Average* 49.5 10.2 85,111 65,678 11.1%/2"
P 1783 V 85,692 .076"P 1785 V 86,874 .072"P 1791 V 86,783 .080"P 1798 V 88,019 .089"Average for Type V Specimens (Kt = 1.0) 86,842 .0793"
P 1806 X 83,540 . 028"P 1813 X 84,270 .026"P 1819 X 84,494 .029"P 1825 X 88, 019 .027"Average for Type X Specimens (Kt = 3.4) 84,089 .0275"
Standard ASTM Specimen and Test.
WADC TR 52-307, Part II - 13 -
TABLE III. STATIC PROPERTIES OF 75S-T6EXTRUDED ALUMINUM ALLOY
Specimen Hardness Mod. E Tensile .2% OffsetNo. and R o Strength Yield Str.
Type RA 106 PSI PSI PSI Elong.
R 1829 AE* 52.4 10.0 93,585 86,166 9.5%/2"R 1830 AE* 52. 6 10.0 93,274 85,740 9.55%/2"R 1831 AE* 52.9 9.9 92,889 85,927 10. 0%/2"R 1832 AE* 52.8 10.1 92,889 86,900 10. 5%/2"R 1833 AE* 51.7 89,287 81,400 8.5%/2"Average* 52.5 10.0 92,386 84,226 9. 6%/2"
R 1838 V 94,193 .073"R 1851 ,V 96,261 .079"Average for Type V Specimens (Kt = 1.0) 95,227 ,076"
R 1875 X 102,853 .016"R 1887 X 99,446 .020"Average for Type X Specimens (Kt = 3.4) 101,150 .018"
Standard ASTM Specimen and Test.
WADC TR 52-307, Part II - 14 -
TABLE IV. FATIGUE DATA ON 14S-T6EXTRUDED ALUMINUM ALLOY
Type V Specimens (Kt 1. 0)
Specimen Stress Ratio Crest Stress KilocyclesNumber A KSI to Failure
Q 1708 V 0.15 70.0 25100., *Q 1714 V 0.15 77.0 778.Q 1724 V 0.15 80.0 669.Q 1718 V 0.15 82.0 0.06Q 1713 V 0.89 29.0 21600. *Q 1707 V 0.89 29.0 2290. *Q 1735 V 0.89 38.0 1910. *Q 1732 V 0.89 42.0 25200. *Q 1723 V 0.89 45.0 216.Q 1706 V 0.89 45.0 101.Q 1719 V 0.89 60.0 114.Q 1729 V 0.89 75.0 19.1Q 1715 V 00 24.0 14100. *Q 1722 V o0 30.0 1080. *Q 1728 V 0o 32.0 2330. *Q 1734 V 0o 34.0 832.Q 1709 V 00 39.0 108.
Type X Specimens (Kt 3.4)
Q 1744 X 0.15 35.0 6570.Q 1740 X 0.15 45.0 368.Q 1737 X 0.15 80.0 16.9Q 1736 X 0.89 16.0 25600. *Q 1742 X 0.89 20.0 184.Q 1739 X 0.89 35.0 12.6Q 1746 X 0.89 55.0 2.16Q 1738 X 0o 11.0 9640.Q 1743 X 0o 20.0 23.7Q 1747 X 0o 39.0 1.8
• Did not fail.
WADC TR 52-307, Part II - 15 -
TABLE V. FATIGUE DATA ON 24S-T4EXTRUDED ALUMINUM ALLOY
Type V Specimens (Kt = 1.0)
Specimen Stress Ratio Crest Stress KilocyclesNumber A KSI to Failure
P 1776 V 0.15 75.0 24300 *P 1771 V 0.15 80.0 864.P 1778 V 0.15 85.0 5600.P 1781 V 0.15 86.0 318.P 1773 V 0.15 90.0 0.3P 1779 V 0.89 42.0 19800.P 1774 V 0.89 50.0 313.P 1772 V 0.89 65.0 39.9P 1775 V 0.89 80.0 9.6P 1782 V 0.89 84.0 7.6P 1780 V 0D 26.0 19900. *P 1777 V o0 30.0 918.P 1784 V co 33.0 584.P 1770 V Co 39.0 150.
Type X Specimens (K-t = 3.4)
P 1810 X 0.15 35.0' 20500.P 1828 X 0.15 40.0 929.P 1804 X 0.15 45.0 382.P 1808 X 0.15 60.0 103.P 1809 X 0.15 75.0 23.8P 1821 X 0.15 83.0 0.06P 1815 X 0.89 16.0 19500. *P 1807 X 0.89 18.0 885.P 1805 X 0.89 25.0 106.P 1827 X 0.89 40.0 11.1P 1800 X 0.89 55.0 3.64P 1826 X 0o 9.5 24600.P 1811 X o0 10.5 4490.P 1803 X 00 12.0 2150.P 1802 X 0D 20.0 170.P 1812 X 0D 30.0 23.8P 1801 X 0D 39.0 4.2
Did not fail.
WADC TR 52-307, Part II 16 -
TABLE VI. FATIGUE DATA ON 75S-T6EXTRUDED ALUMINUM ALLOY
Type V Specimens (Kt = 1,0)
Specimen Stress Ratio Crest Stress KilocyclesNumber A KSI to Failure
R 1843 V 0. 15 80.0 24100. *R 1835 V 0.15 85.0 454.R 1839 V 0.15 90.0 356.R 1860 V 0.89 25.0 19600. *R 1834 V 0.89 29.0 20500. *R 1837 V 0.89 40.0 6980. *R 1853 V 0.89 50.0 292.R 1840 V 0.89 70.0 55.6R 1841 V 0o 25.0 26900. *R 450 V 0D 29.0 4880.R t836 V co 39.0 248.
Type X Specimens (Kt = 3.4)
R 1892 X 0,15 31.0 20200. *R 1870 X 0.15 34.0 'I750.R 1874 X 0.15 35.0 1400.R 1866 X 0.15 38,0 1300.R 1878 X 0.15 60.0 56.4R 1882 X 0.15 90.0 12.9R 1868 X 0.89 15.0 21000.R 1872 X 0.89 20.0 206.R 1864 X 0.89 40.0 6.12R 1865 X 0D 10.5 15400.R 1869 X 0o 15.0 540.R 1873 X 0o 35.0 5.76
,Did not fail.
WADC TR 52-307, Part II - 17 -
14 ,
a. 754S-T6 Longitudinal Section 10OX d. 14S.-T6 Transverse Section l00X
WADC TR 5237 at I-1
*x
zoo-:z
0 U)
4-,w
- 0
0.0z010 wtot
w wU. a.
N
0 0 i.Z 0 U) <L
Y- - 2
0 0 *-0 Iz M
0-00 0 z
0 zo -0
(nI( I ýl 0 2c>' 00a
a. 0 ~ IZ
1 04n z
Z CD Z~z z 06--
w OOO
-T ý1 cnU-
WADC TR 52-307, Part Il 19-
I00
In42T0 SO--
-- 60
I,, 30 w
VIl
10%
P 1tN T AND LINE CODEx
•A 2.1S - -6- -A 0 - -
1 0 A• 0.3,7 . .. 4. . .
SA 0 .15 ---- (D ..9 A _ _ 0 .0_. . "- * - -...... E-.
1 5 14 5 I t0o5 O 5 10 ? I0
NUMDER Of CYCLES TO FAILURE (LOG SCALE.)
FIG.3. SI-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR K tz 1.0
SPECIMENS OF ALUMINUM ALLOY 14S- T6. (EXTRUDED)
9 0
70
60:- -O -_ _ _ _ _ _
40 1
z
goo,POINT AND LINE CODE
4A CC~
A * 2.16 ------
A 0 069 --- "-----
1 I0 A 0.37 ---.T-----A * 0.15 ---- "-"_....A ox .a- ------- --------
4 ? 5 Sto 5 10 5 10 5 10 5 0 5 10
NUMBER OF CYCLES TO FAILURE (LOG SCALE)
FIG.4. S-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR Kt: 3.4SPECIMENS OF ALUMINUM ALLOY 14S- T6 (EXTRUDED)
WADC TR 52-307, Part 11 - 20 -
S.S-RATIO OF MEAN STRESS TO STATIC ULTIMATE STRENGTH (EXTRUDED)
0 0.1 02 0.3 0.4 0.0 0.6 0~7 0.6 0.9 1.0
60 FATIGUE STRENGTHS
_b CYCLES IDENTIFIED4lot BY 4, 5, S7 RESP.
s0o- - - ROLLEDw
____ EXTRUDED 1.5 14
300
Ci,,
10 - imp0t-et
04010 20 3 0 so s ro t 0
m MENSRES Kl
5so FAIU STANRTRSSTHSS
FIG.A- CY LE IDTRESSE RA0 ATG E DAG A O
Kr 10 SPCIMES OFEXTRDED LUMINM ELLOYRUDED
AT IO'" 10S O
Z -I-
10
7 I5
S z -__- - -o-- -- -
S, ME-- -TRESS -- - - -
=I-.-SRS AG A IU IGA Ow ~ 34SEIESO XRDE LMNMALY1S T
WACT 237 Pr I-2
S60---zw
50 v---------Is0 1-- - - - - - - - - - - - - - - 1
zz
z _.4
20
08 10 t0 30 40 50 60 70 %s 90 10o
msMEAN STRESS IN UNNOTCHED SPECIMEN, KuI
FIG. 7. FATIGUE STRENGTH - REDUCTION "CONTOUR" CURVES FOR
Kt- 3.4 SPECIMENS OF EXTRUDED ALUMINUM ALLOY 149 -f
SHOWING KfAS A FUNCTION OF SaAND SOF THE UNNOTCHED SPECIMEN
K s0.
.6----- - 00 - - - - - -. 25
.1.
.4 ________ ode- -__ .43_ ___ __
0
to -. 4 23w
S -. 6 - .0
-1.0 f al0b 104
10 a 10OS 10'
N NUMBER OF CYCLES TO FAILURE
FIG.S. FATIGUE STRENGTH REDUCTION "CONTOUR" CURVES FORKt '1.0 SPECIMENS OF ALUMINUM ALLOY 14S-T6 (EXTRUDED)
SHOWING Kf AS A FUNCTION OF N AND STRESS RATIO R
WADC TR 52-307, Part 11 22-
9 80 n-.-- ---, D
070o ,= _
60
S50
- 40,.40 __"--e -
z
20hi.
10%
POINT AND LINE CODE
4 A CCA * 2.16 -----
A 089 --------
10 A * 0.37 - -- ....
A 0.15 -------..A O.c 0 -------
3 4 ?10 5 10 5 10 5 10 5 10 5 10
NUMBER OF CYCLES TO FAILURE (LOG SCALE)
FIG.9. S-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR Kt: 1.0SPECIMENS OF ALUMINUM ALLOY 24S-T4 (EXTRUDED)
'A
00o
0760
-G
50
,- 40 "'",- .__
w20
S10%
POINT AND LiNE CODE
4 A OCA 2.16 ---- 0----
A 089 --
10 A 0.37 ----- 0-----
A 0.15 ---------A O.C a_---.---- ....
3 1 4 610 5 50 10 5 I0 5 10 5 0
NUMBER OF CYCLES TO FAILURE (LOG SCALE)
FIG. IO.S-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR Kt=3,4SPECIMENS OF ALUMINUM ALLOY 24S-TT4 (EXTRUDED)
WADC TR 52-307, Part II - 23 -
S./S,- RATIO OF MEAN STRESS TO STATIC ULTIMATE STRENGTH (EXTRUDED)0 0.1 0.2 03 0.4 O5 0.6 0.7 0.8 0,9 1.0
so FATIGUE STRENGH. S" -,,AT 10,o 105, S Io OT 0___CYCLES IDENTIFIEDI~ ,• Y 4, 5, & 7 RESP. ' O2.u 0o
50ROLLED ,w
"4 EXTRUDED
£w
I~~s t ""•t Wa-
00
1 0 0 o 3 0 5 6 O9 0
Sm MEAN-. TS -. S-F IG .I- I S S RAG FI -D
I 0 Ito 30 40 sEo 60 TO so 90 100
Sm- MEAN STRESS -- KSI
FIG. Ih - STRESS RANGE FATIGUE DIAGRAM FOR
Kt,1.0 SPECIMENS OF EXTRUDED ALUMINUM ALLOY 24S-T6
Sm/Su- RATIO OF MEAN STRESS TO STATIC ULTIMATE STRENGTH (.EXTRUDED)0 0.1 0.2 0.3 0.4 05 0.S 0.7 0.69 0. 1,o
so FATIGUE STRENGTHS
AT 104 IO1, & 107 I •CYCLES IDENTIFIED 4
; /• BY 4, 5, lk 7 RESP. "50 ROLLED w
EXTRUDED i
44
40 4z
.N
• A 3.0.- -
0 W
010.0 030 40 !0 50 70 SO SO 100
$m- MEAN STRESS- KS1
FIG.12.- STRESS RANGE FATIGUE DIAGRAM FORKt,5. 4 SPECIMENS OF EXTRUDED ALUMINUM ALLOY 24S- T6
WADC TR 52-307, Part II -24 -
0 _ _
z
3 o
K .0
0 0 t 30 0 50 s 0 a0 19 10
SoMAzTIS I NOCE PCMN S
FI.1.FTGE SRNT EDCIN"OTU"CRE O
Kt1. 30CMN FEXRDDAUIUMALY25 T
SHWN S U-INOFSaADS
OF TH _NTH PEIE
.4 2.0 46430 0 7 S60
Mt .0 t.48I UNTHD PCMN
.0 .
22
o 0I-
0 1. as
Kt 3.4 2.33MEN OFAUIU ALY2S 4(XRDD
SHOWING ~ ~ KASAFNUMBEN OF CYCLES STO ES FAL RATO
WADC TR 52-307, Part II - 25 -
100 -*- __
o 0 so
0 70
o
60 -N
50
04z
20hI
10%I
P 0 POINT AND LINE CODEx4 A CC
A 2.16 ------
A 089 ---- •------
10 l A 0.37 ---. 0----..
9 A 0 .15 -- - - - -" . .. .A O.C a ---.-.---
+34 5 7" 8t0 5 10 5 10 5 10 5 10 5 10
NUMBER OF CYCLES TO FAILURE (LOG SCALE)
FIG.15. S-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR Kt= 1.0
SPECIMENS OF ALUMINUM ALLOY 75S-T6 (EXTRUDED)
100 .Su 101.2 KSI
~,904
70 %0 - ------
Z!60 -
o 50
-J
>. 40
U
0
" ~ 3 00 9_--_--
in20
P0 01•N _ AND LINE CODE
d)A 2 .16 - -'(-. .
90 A =$ 0%
A ox 0.3 -------- 0.1 eF -
3 4 56to 5 10 5 0 5 I0 5 10 10
NUMBER OF CYCLES TO FAILURE (LOG SCALE)
FIG. 16. S-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR . Kt .4
SPECIMENS OF ALUMINUM ALLOY 75S-T6"(EXTRUDED)
WADC TR 52-307, Part II - 26 -
To RATIO OF MEAN STRESS TO STATIC ULTIMATE STRENGTH (EXTRUDED)
IoI 1_7 FATIGUE STRENGTHSI ATI104 O',&S107
__ ___CYCLES IDENTIFIED44 0*Y 4, 5, & 7 RESP.
-0 - - - ROLLEDN___ EXTRUDED
w
2.-1
4'e
00 10 t0 30 40 506 70 TO so 0O
S,- MEAN STRES5 - (SI
FIG.17. - STRESS RANGE FATIGUE DIAGRAM FORK= 1. SPECIMENS OF EXTRUDED ALUMINUM ALLOY 75S-T6
Sm/Su, (RATIO OF MEAN STRESS To STATIC ULTIMATE STRENGTH)
O 0.1 og2 0:3 0.4 05 0.6 0.9 11 ~s I0
60FATIGUE -STRENGTHS 0
AT IOeIOps 10?- -- -CYCLES IDENTIFIED U)
BY 4,5, &7 RESP. .
500
EXTRUDED
I40 - -I4O
0 0
SO+mG -30 LL4- c
IT
4*4I
Nm MEN ST ES.
FIG.8.. STR SS RANEA FATIGES DSIAGA O
K 3.4 SPECIMENS OF EXTRUDED ALUMINUM ALLOY 75S - T6
WADC TR 52-307, Part II - 27 -
0o
z
1- 0
000 3 0 5 0 7 0 9 0
E 30
1.0 -0
to 2.0
__107 U1
o 0/
Kf t.9-
__ 10 t_3_050 g_0 o 9 100
-- 7 K2.3 0.4
08 9.0
-2 ~ 0__ _ _ _ _ _ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _
103 10 101 log 10,
N NUMBER OF CYCLES TO FAILURE
FIG.20. FATIGUE STRENGTH REDUCTION "CONTOUR" CURVES FORKt1.0 SPECIMENS OF ALUMINUM ALLOY 755 -T6 (EXTRUDED)
SHOWING Kf AS A FUNCTION OF N AND STRESS RATIO R
WADC TR 52-307, Part II - 28 -
NN
60 N,
10 YCLES _
NI
50 NN~. -- - F---- ---- ----
4 0 N-
9 0z
10 20 30 40 50 60 70 s0 90 100 110
4C _ -................3nU-.--- -
Sm< - MENSRSSIKI
FIG.21. STRESS - RANGE DIAGRAMS SHOWING COMPARATIVE
FATIGUE STRENGTHS OF EXTRUDED ALUMINUM ALLOYS
WADC TR 52-307, Part II - 29-