WADC TECHNICAL REPORT Part II · 2018-11-09 · WADC TECHNICAL REPORT 52-307, Part II FATIGUE...

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

NOTICES

When Government drawings, specifications, or other data are usedfor any purpose other than in connection with a definitely related Govern-ment procurement operation, the United States Government thereby incursno responsibility nor any obligation whatsoever: and the fact that the Govern-ment may have formulated, furnished, or in any way supplied the said draw-ings, specifications, or other data, is not to be regarded by implication orotherwise as in any manner licensing the holder or any other person or cor-poration, or conveying any rights or permission to manufacture, use, orsell any patented invention that may in any way be related thereto.

The information furnished herewith is made available for study uponunderstanding that the government's proprietary interests in and relatingthereto shall not be impaired. It is desired that the Judge Advocate (WCJ),Wright Air Development Center, Wright-Patterson Air Force Base, Ohio,be promptly notified of any apparent conflict between the Government's pro-prietary interests and those of others.

The U. S. Government is absolved from any litigation which may en-sue from the contractor's infringing on the foreign patent rights which maybe involved.

WADC TECHNICAL REPORT 52-307, Part II


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


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.


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).


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


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.


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. 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).


6.4.1 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


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.


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.


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.


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.


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.


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.


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.


TABLE V. FATIGUE DATA ON 24S-T4EXTRUDED ALUMINUM ALLOY

Type V Specimens (Kt = 1.0)


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)


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.


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


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


FIG. IO.S-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR Kt=3,4SPECIMENS OF ALUMINUM ALLOY 24S-TT4 (EXTRUDED)


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


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


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


FIG. 16. S-N FATIGUE DIAGRAMS AT VARIOUS STRESS RATIOS FOR . Kt .4

SPECIMENS OF ALUMINUM ALLOY 75S-T6"(EXTRUDED)


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


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


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 TECHNICAL REPORT Part II · 2018-11-09 · WADC TECHNICAL REPORT 52-307, Part II FATIGUE...

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Transcript of WADC TECHNICAL REPORT Part II · 2018-11-09 · WADC TECHNICAL REPORT 52-307, Part II FATIGUE...