National Bureau of Standa ds

Library, N.W. Bldg

SEP 2 2 1360

^ccltnicuL ^^ote

PB 161556

taken from tlie Library.

55

INVESTIGATION OF BEARING

CREEP OF TWO FORGED

ALUMINUM ALLOYS

U. S. DEPARTMENT OF COMMERCE

NATrONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

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maintenance of the national standards of measurement and the provision of means and methods for

making measurements consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing materials, devices,

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NATIONAL BUREAU OF STANDARDS

technical Viote

55

AUGUST 1960

INVESTIGATION OF BEARING CREEP OF TWO

FORGED ALUMINUM ALLOYS

Leonard Mordfin, Nixon Halsey, Philip J. Granum

Report to

Bureau of Naval Weapons

Department of the Navy

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Price $1.00

IMVESTIGATION OF BEARING CREEP OF TWO

FORGED ALUMINDM ALLOYS

Leonard Mordfln^ Nixon Halsey and Philip J. Granum

Fourteen bearing specimens of 7075-T6 and

2014-T6 forged aluminum alloys were tested in

creep at 400"" F. The 2014-T6 specimens had

greater creep resistance and less ductility than

the 7075-T6 specimens.

For each material the bearing creep resistance varied directly with edge distance and bolt

tightness. Prior exposure of the 2014-T6 alloy

to elevated temperature reduced its bearing creep

resistance.

The validity of a previously proposed theory

of creep in bolted joints was examined using the

test data together with results from an earlier

study. The theory was found to hold for 7075-T6

but not for 2014-T6.

1. INTRODUCTION

The investigation described herein is one of a series intended to

obtain useful solutions to structural creep probloas by the quantitative

relationship of structural creep to material creep.
- 2 -

A limited test program was undertaken to obtain data on bearing creep

deformation for 7075-T6 and 2014-T6 forged aliunlnum alloys. The Immediate

objectives were (1) to explore the general nature of bearing creep In

these materials, and (2) to examine the feasibility of calculating the

creep deformations In large bolted joints which are expected to fall in

bearing. In connection with the latter objective. It was proposed In an

earlier report (ref. 1) that:

A joint which Is expected to fall In bearing can

usiially be considered to creep only In bearing.

The elongation of the joint, then, is the same as

that for a simple bearing specimen having the same

edge distance and subjected to the same stress and

temperature as the joint.

The creep deformations obtained with the bearing specimens tested in this

investigation are compared with the creep deformations obtained with

7075-T6 and 2014-T6 bolted joints (fig. 1) tested in a previous study.

The details of the bolted joint tests are reported elsewhere (ref. 2),

but are summarized, for convenience, in Appendix A.

This report describes the material bearing creep test program and

the results obtained. This investigation was conducted at the National

Bureau of Standards vinder the sponsorship and with the financial assistance of the Bureau of Naval Weapons. The authors acknowledge the

assistance of Mr. Thomas D. Field, Jr. in the design of some of the test

apparatus.
- 3

-

2. SPECIMENS

The bearing specimens tested in this investigation were cut from the

bolted joints described above and in Appendix A. They were machined from

parts of the straps which had been subjected to relatively little heating.

It is estimated that those portions of the straps from which the bearing

specimens were taken had not been heated above 200° F and had not been

stressed beyond the elastic limit corresponding to this temperature.

Hence the bearing specimens did not have any prior work hardening, but

undoubtedly did have a small amount of overaging because of the exposure

to elevated temperature.

Two general designs of bearing specimens were tested. These are

designated as "straight" and "beveled", and are shown in figs. 2 and 3.

The beveled specimen is an attempt to reproduce the complex edge condition of the bolted joint specimens.

3. TEST TECHNIQUES

3.1 Loading

The tests were conducted in a 100,000 lb capacity universal screwpower testing machine, which was adapted for creep testing by the installation of a load-maintaining system similar to that described in ref. 4.

Referring to figs. 4 and 5, the specimen A was held by two steel

plates B which were mounted in the upper grip of the machine and separated

by a spacer plate (not shown). The bearing load was applied with a hardened steel pin C which was machined to provide a close sliding fit in the
- 4 -

bearing hole. The pin was held by two steel plates D which were mounted

In the lower grip of the testing machine and separated by a spacer plate

(not shown).

The ends of the loading pin were threaded to accommodate nuts E.

These could be tightened to simulate bolt tightness In a joint. "Full"

tightness could be Imposed by Inserting washers F and drawing the nuts

up tight with a wrench. A condition of "no" tightness could be effected

by removing some of the washers and leaving the nuts loose.

3.2 Deformation Measurement

Bearing deformation manifested Itself primarily as an elongation of

the bearing hole. This deformation was measured In terms of the displacement of the axis of the loading pin from the axis of the original

hole.

A concentric rod and tube arrangement was used to transfer the displacement to the outside of the test furnace. Referring to figs. 4 and

5, tubes G were mounted parallel to each edge of the specimen. The upper

ends of these were fixed on the original horizontal center line of the

hole by set screws H. A rod inside each tube was attached to a yoke

device which included plates J. These plates had holes drilled In them

so that they fitted closely over the loading pin.

Displaconent of the pin relative to the original bearing hole was

thus converted into a differential movement within each of the two rod

and tube assemblies. This movement was measured with a pair of differential transformers mounted on the lower ends of the rods and tubes below
- 5

-

the test furnace. Strip chart recorders were used to obtain records of

displacement vs. time. The bearing deformation of the specimen was taken

as the average of the two records.

3.3 Heating

The test furnace was fabricated from trans ite sheet and contained

eight quartz infrared lamps. Four thermocouples were peened into the

surface of each specimen. The voltages to the lamps were controlled by

autotransformers. These were adjusted maniially to minimize temperature

gradients. Power was controlled by a time- proportioning automatic temperature controller.

Temperatures were maintained constant and uniform within 2° F during

each test.

3.4 Testing Procedure

After heating the specimen to the test temperature^ it was permitted

to remain at that temperature for a predetermined exposvire period. The

test load was then applied, and this was considered time zero. Deformations were measured starting at the time that the full test load was

reached. In this manner, displacements due to elastic extension, thermal

expansion and backlash in the extensometer arrangement, were eliminated.
- 6 -

4. NOMENCLATURE

4. 1 Symbols

D diameter of loading pin^ in.

e base of natural logarithms, 2.718 ...

f- , f_ fxmctions of t

1' 3 X

f~ fxmction of t^-.

F test load, lb

h thickness of bearing specimen, in.

k characteristic dimension of beveled specimen (see fig. 3), In.

m edge distance, in. or dimensionless (see Section 4.2)

m r:f effective edge distance, in. or dimensionless (see Section 4. 2)

P a parameter defined by eq. (2)

P' a parameter defined by eq. (4)

R bolt tightness (see Section 4.2)

t prior exposure time, hx (see Section 4.2)

t.- test time to reach 0.10 in. of creep extension, hr

a bearing stress as defined by eq. (1), or bearing creep strength,

lb/ in?

a' bearing creep strength for t =0, lb/in?

4. 2 Definitions

Bearing stress , a, is the compressive stress produced on the edge

of the bearing hole by the loading pin. For most design purposes this
b

. 7

-

stress is considered to be uniformly distributed over the projected area

of the edge of the hole^ so that

Edge distance, m, is the distance from the center of the bearing

hole to the edge of a straight specimen^ measured in the direction of

loading (see fig. 2). Very often^ edge distance is expressed dimensionlessly as the ratio of edge distance to pin diameter. In this investigation the diameter is 1 in. ^ so the two representations are equivalent.

For a beveled specimen (fig. 3), the above definition does not apply

so an effective edge distance^ m ^^, must be used.

Prior exposure , t , is the length of time that a specimen is subjected to the test temperature prior to the application of the test load.

Bolt tightness

t

R, has been assigned a numerical scale from 1 to 10

where 1 represents no tightness and 10 represents full tightness.

5. TEST RESULTS FOR 7075-T6 SPECIMENS

AND DISCUSSION

5.1 Straight Bearing Specimens

Five straight specimens (fig. 2) of 7075-T6 aluminum alloy were

tested at 403° F to explore, in a cursory manner, the effects of bearing

stress, edge distance and bolt tightness on bearing creep deformation.

These tests were all conducted with a prior exposure to test temperature

of 1.7 hr. The test conditions are listed:
- 8 -

Specimen No. m

in.

R a ho

lb/in? hr

4 2.00 1 35,000 1.1

5 2.62 1 35,000 7.1

6 1.85 1 30,800 10.5

7 1.85 10 35,000 3.4

8 1.85 10 35,000 3.3

The creep deformation curves are given in fig. 6. These were condensed from the continuous strip chart records. The curves do not exhibit

a conventional steady- state creep stage, nor do they plot as straight

lines on log paper. Hence, neither steady- state creep rates nor simple

power functions could be iised to characterize the curves. Instead, t^.,

"the test time required to reach 0.10 in. of creep deformation", was arbitarily chosen as a simple measure of creep resistance by which the curves

could be compared. Values of t.- are listed in the table above.

Using the data in the table, it was deduced that the relative effects

of stress, edge distance and bolt tightness could be adequately described

by means of the empirical parameter

P . to^Oe-'/lOOO (2)

This parameter was related to t^_ with a curve- fitting process, giving

the empirical equation
t^o - lo^p°•^ (3)

A comparison of this equation with the experimental data Is shown In

fig. 7.

Neither eq. (2) nor eq. (3) has any value except for the specimens

and the range of variables Involved here. The equations are used In this

report merely to show the relative effects of the different test variables

and to facilitate Interpolation of them.

Examination of eqs. (2) and (3) reveals that creep resistance decreases rapidly with Increasing bearing stress. Increasing edge distance

raises the creep resistance^ even for values as high as 2.62. Furthermore^ bolt tightness Increases the creep resistance.

The strengthening effect of bolt tightness^ Insofar as creep Is concerned^ Is one that has received little consideration as revealed by the

literature. This effect is discussed further In the following section.

5.1.1 Effect of Bolt Tightness

Intuitively^ It seems that bolt tightness Improves bearing creep

resistance by (1) diverting some of the nominal bearing force toward

overcoming friction between the faying surfaces^ (2) restraining lateral

deformation in a direction parallel to the bolt axls^ or (3) both.

Yerkovlch^ in reporting the results of creep tests on riveted

joints, ref. 3, attributed the Improvement in bearing creep resistance

to friction between the faying surfaces.
- 10 -

The tests of specimens 7 and 8 were designed to Investigate this

effect. The conditions for these two tests were Identical with one

exception. The washers (F^ fig. 5) for specimen 7 were steel while those

for specimen 8 were alijmlnum. This difference was Introduced to examine

the effect of friction between the washers and the specimen. The coefficient of sliding friction for an alumlnum/alumlnijm Interface Is about

three times that for an aluminum/steel Interface^ ref. 6. Nevertheless,

fig. 6 shows that the creep curves are virtually Identical.

This suggests only one explanation: Bolt tightness Improves the

creep resistance of the bearing specimens by restraining lateral deformation In a direction parallel to the bolt axis. This deformation Is

Illustrated In fig. 8. Specimens 4 and 9, fig. 8, are both 7075-T6 aluminum alloy; specimen 4 was tested with no bolt tightness while specimen

9 had full bolt tightness. In the former case considerable lateral deformation Is apparent; In the latter case, comparatively little.

As a result of this effect, the proposition presented on page 2 must

be broadened. Specifically, the word "stress" should be Interpreted to

Include lateral restraint as well as nominal bearing stress.

5.2 Beveled Bearing Specimens

Two beveled specimens of 7075-T6 alimilnum alloy were tested to evaluate the effective edge distance for this design. Both tests were conducted at 403° F following a prior exposure of 1.7 hr, with a nominal

bearing stress of 35,000 Ib/lnf and full bolt tightness. The dimensions

k (fig. 3) and the test results obtained were:
- 11 -

Specimen k

in.

ho

hr

9 2.50. 3.0

10 2.62 4.6

The values of t- were taken from the creep deformation records,

which are reproduced in fig. 9. With these values, the parameter P for

each specimen was taken from fig. 7. Then, with eq. (2), it was calculated that

m

e

-^ = 1.83 in. for specimen 9, and

m ^<- = 1.96 in. for specimen 10.

eff

A comparison of these values with the dimension k reveals that ^ 3 , eff 4

3.3 Bolted Joint Specimen

The 7075-T6 bolted joint specimen which was discussed in the Introduction and in Appendix A had an edge condition similar to that of specimen 10. Furthermore, it was tested under the same stress and temperature

conditions as specimen 10. Hence, according to the proposition on page

2, the joint should yield the same creep curve as specimen 10. The creep

curves for the joint and for the bearing specimen are given in fig. 10,

from which it is apparent that some discrepancy exists between the two.

For design purposes, it is desirable to evaluate the magnitude of

this discrepancy in terms of stress. From the curve for the bolted joint
- 12 -

it is seen that t^. = 6.0 hr. Entering fig. 7 with this value gives

-12

P = 8.0 X 10 . Now, using m ^^ = 1.96 in. and R = 10, eq. (2) shows

that the effective bearing stress for the bolted joint is 34,600 lb/in?

This is only 1.1 percent less than the actual bearing stress and represents a stress-wise error that is generally negligible.

6. TEST RESULTS FOR 2014-T6 SMCIMENS

AND DISCUSSION

6. 1 Bearing Specimens

Seven bearing specimens of 2014-T6 alimiinum alloy were tested at

398° F. The test conditions are listed in the table below and the creep

curves are given in fig. 11. Examination of these data reveals that the

creep properties of 2014-T6 are superior to those of 7075-T6 at 400° F.

An additional test variable, prior exposure time, was introduced in

this series of tests. Because of this additional variable, the parameter

P, defined by eq. (2) must be modified to incorporate the effects of

prior exposure as follows:

P' = P(H-t^)"°-® (4)

The exponent in this equation was determined by a curve-fitting process.
- 13 -

Tests of 2014-T6 Bearing Specimens

Specimen Type m k R t

X

hr

cr ho

in. in. lb/in? hr

3 S 2.00 b 1 1.7 50,000 5.0

11 B b 2.62 10 48.4 50,000 4.8

12 B b 2.62 10 1.7 50,000 20.4

13 B b 2.62 10 48.4 34,000 c

14 B b 2.62 10 48.4 46,700 22.0

15 S 2.62 b 10 48.4 46,700 27.7

16 B b 2.62 10 1.7 46,700 27.0

a. S = straight; B = beveled

b. Not applicable

c. Test discontinued at 116 hr, before reaching 0.10 in.

of creep.

A plot of t^_ vs. P' for the 2014-T6 bearing specimens is given

in fig. 12. The dashed line was faired through the plotted points.

The parameter P' is empirical, and only applies to the specimens

and the range of variables discussed here. It is used in this report only

to indicate the relative effects of the different test variables on the

creep resistance of the bearing specimens.

It may be seen that bearing stress, edge distance and bolt tightness

affect the creep resistance of the 2014-T6 specimens in the same general

manner in which they affected the creep resistance of the 7075-T6 specimens,

Furthermore, the creep resistance of the 2014-T6 specimens is reduced by
- 14 1

increasing the prior exposure time. The nature of this reduction is

discussed further in the following section.

6.1.1 Effect of Prior Exposure

It was postulated in ref. 2 that, for a given material at a given

temperature,

a = f^a' (5)

where a is creep strength following an exposure, g' is creep strength

without a prior exposure, and f- is a function of the exposure time

only.

Based on the data obtained in this investigation, it is shown in

the Appendix that

o = a' - f^ (6)

where f_ is a function of the exposure time only.

It is obvious that eqs, (5) and (6) are not compatible. In all

probability, eq. (5) is incorrect, but eq. (6) should not be employed for

design purposes without obtaining further experimental verification.

6.2 Bolted Joint Specimen

The 2014-T6 bolted joint specimen which was discussed in the Introduction and in Appendix A had an edge condition similar to that of specimen 11. Furthermore, it was tested under the same stress, temperature

and exposure conditions as specimen 11. A comparison of the creep curves
- 15 -

for the bolted joint and for specimen 11 is given in fig. 13. It is

clear from this figure that virtually no correlation exists between the

two^ indicating that the proposition on page 2 does not apply in this

case.

This is not entirely unexpected^ and was foreseen some time ago in

ref. 7. The theory holds only for ductile materials which have the

ability to rapidly relax the stress concentrations around holes by plastic flow^ while still retaining considerable creep strength and ductility

(ref. 8). At 400* F, however, 2014-T6 is relatively brittle in creep,

and presumably does not permit the relief of stress concentrations prior

to fracture. The presence of this relative brittleness is evidenced by

fig. 11, which indicates small valiies of extension at rupture, and by

fig. 8, where specimens 3 and 16 are 2014-T6 and specimens 4 and 9 are

7075-T6.

What is surprising is that the joint exhibited greater creep resistance than the corresponding bearing specimen, fig. 13. Studies of the

possible effects of overaging, interaction between bolt holes in the

joint, oversized holes, and multiaxlality of stress were made in an

attempt to explain this apparent anomaly. However, to date the authors

are unable to offer a rational explanation for this unusual behavior.

7. CONCLUSIONS

The bearing creep properties of 2014-T6 forged altmiinum alloy are

superior to those of 7075-T6 forged alimintmi alloy at 400° F. At this
- 16 -

temperature, 2014-T6 exhibits considerably less ductility than 7075-T6.

These conclusions corroborate similar ones obtained in ref. Z.

Based on the lisulted number of tests performed, it appears that the

bearing creep resistance af the tvo alloys Increases both with Increased

edge distance and with Increased bolt tightness. The ben^lclal effect

of bolt tightness is seemingly due to restraint of lateral deformation

in a direction parallel to the bolt axis, rather than to friction. Exposure of 2014-T6 to elevated temperature for a period af time prior to

loading apparently reduces the bearing creep resistance.

The creep strsigth of a 7075-T6 bolted joint, which had been designed

to fall in bearing, was found to agree closely with the creep strength of

a 7075-T6 bearing specimen under the same edge, stress and temperature

conditions.

The creep resistance of a 2014^T6 bolted joint was considerably

greater than that of a comparable bearing specimen.
- 17 -

8. REFERENCES

1. L. Mordfln and A. C. Legate^ "Creep Behavior of Structural Joints of

Aircraft Materials Under Constant Loads and Temperature8*%

NACA TN 3842, 1957.

2. L. Mordfln, G. E. Greene, N. Halaey, R. H. Harwell, Jr., and

R. L. Bloss, "Creep and Static Strengths of Large Bolted Joints of

Forged Aluminum Alloys Under Various Temperature Conditions",

NBS Rep. 5442 on BuAer Project TED NBS AD-222, July 1957, unpublished;

also IAS Paper 779, 1958.

3. L. Mordfln, "Creep and Creep-Rupture Characteristics of Some Riveted

and Spot-Welded Lap Joints of Aircraft Materials", NACA TN 3412, 1955.

4. A. H. Stang and L. R. Sweetman, "Speed Control for Screw-Pover Testing

Machines Driven by Direct-Current Motors", ASIM Bui. No. 87, Aug. 1937.

5. L. A. Yerkovlch, "Investigation of the Compressive, Bearing, and

Shear Creep-Rupture Properties of Aircraft Structural Metals and Joints

at Elevated Temperat\ires", VADC TR 54-270, Part IV, May 1958.

6. T. Baumelster (ed.), "Marks' Mechanical Engineers' Handbook",

McGraw-Hill Book Co., New York, N. Y., 6th ed., 1958, p. 3-40.

7. L. Mordfln, "The Creep of Structtiral Joints", Proc. Fla. Conf. on

High-Speed Aerodynamics and Structures, ARDC TR 57-46, vol. 1, 1957.

8. L. Mordfln, N. Halsey and 6. E. Greene, "Effects of Concentration and

Interaction of Stresses on Tensile Rupture Strength of Riveted Joints",

Appendix A to "Investigations of Creep Behavior of Structural Joints

Under Cyclic Loads and Temperatures", NASA TN D-181, 1959.
- 18 -

APPENDIX A

SQMMABY OF PERTINENT INFORMATION FROM R£F. 2

Bolted Joints^ fig. 1^ were fabricated from forged aluminum alloy

slabs and high strength steel bolts. They were creep tested under constant loads and temperatures following an unloaded exposure to the test

temperature. The test conditions were as follows:

Joint material Prior exposure Temperature Bearing stress

hr °F lb/in?

7075-T6* 1.7 403 35,000

2014-T6* 48.4 398 50,000

The 7075-T6 joint exhibited considerably more ductility than the 2014-T6

joint. By using the joint efficiencies in the manner described in ref.

3, the failure times were calculated from the tensile rupture properties

of the materials. Agreement between the calculated and the actual failure

times was satisfactory, as shown:

Joint Actual failure Calculated failure

hr hr

7075-T6 9.6 8.7

2014-T6 31. 25.

*In ref. 2 these joints were designated as 7075-T6-3 and 2014-T6-3,

respectively.
- 19 -

APPENDIX B

DERIVATION OF EQUATION (6)

Substituting eq. (2) into eq. (4) and solving for a gives

a » 1000 [log(Rm^°) - 0.8 log(l+t ) - log P'] (7)

L From fig. 12 it is seen that P' is a function of t-_. Hence

a = 1000 [log(Rm^°) - 0.8 log(l+t^) - £2^*^10^^ ^^^

When t =0, the creep strength reduces to

0' - 1000 [log(Kin^°) - f2^^10^^ ^^>

Substituting eq. (9) into eq. (8),

a = a' - 800 log(l+t ) (10)

a = a' - f3 (6)

where f^ is a function of the exposure time.

USCOMM- NBS- DC- 24, 029
o

UJ

Q.

COOo

UJ

I-

_Iom

g»

*u_
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o

c

(O

c

E

c

E

o

<b

Q.

(O

C3»

'»_ o

<u Si

o

COo

(A

O

O

CMo»
o

c

c

o

'toc

Of£

c

E

'u

a<oo»

'v.O

a>

"O

>

o

u» "5

4-

a

rog»

li.
^ w

'

%

1>^ D

i

1

iu r 1 lace rernov ed
Fig. b - Edge view of test set-up with furnace removed.
0.35 f0.30 -

0.25 -

9>U

- 0.20 - c

o

'inc«^-X

a.«o

0.15 -

0.10-

0.05-

Spec No. 4

Time, hours

Fig. 6 Bearing creep curves of 7075 -T6 straight specimens.
I4i12 -

10-

PxlO'

Fig. 7 Creep resistance of 7075-T6 straight specimens in

parametric form.

0.35i0.30-

0.25-

- 0.20

c

o

M

C

a>

>ca>Q.

Of0)

0.15 -

0.10-

0.05-

Time, hours

Fig. 9 Beoring creep curves of 7075-T6 beveled specimens.
0.35 r0.30 -

0.25 -

<0

01u

c

^Q

0.20

o

c

X 0.15

Q.

0)

01

0.10 -

0.05

7075 -T6 bolted joint specimen

Bearing specimen 10

4 5

Time, hours

Fig. 10 Comparison of creep curves for 7075 -T6

bolted joint end bearing specimen 10.
O.I6f0.14 -

0.J2 -

(O

9> jC 0.10

u

c

^c

o

0.08

o

X

9ta.

a> 0.06

u

0.04 -

0.02 -

15

10 15 20

Time, hours

25 30

Fig. II Bearing creep curves for 2014- T6 specimens
28r

24 -

20

16 -

12-

8 -

i

spec. No. 15

/

/

/

/

/

16

/

0/

/

/

/o 14

/

/

/

/

/

/

II cfi

10 100

P'xIO'^

398°F

J

000 10.000

Fig. 12 Creep resistonce of 2014- T6 specimens in

parametric form.
O.I6r0.14

u

c

(0c

X

0)Q.

0.12

0.10

0.08

0.06

0.04

0.02

2014- T6 bolted joint specimen

Bearing specimen II

398° F

Time, hours

Fig. 13 Comporison of creep curves for 20i4-T6 bolted joint

ond beoring specimen II.
U.S. DEPARTMENT OF COMMERCE

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Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Molecidar Kinetics. Free

Radicals Research. Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. SoUd State Physics. Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

Energy Radiation. Nucleonic Instrumentation. Radiological Equipment.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry. Inorganic

Chemistry. Electrodeposition. Molecular Structure and Properties of Gases. Physical Chemistry. Thermochemistry. ' Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Fluid Mechanics. Engineering Mechanics. Mass and Scale. Capacity, Density, and Fluid Meters. Combustion Controls.

Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Poly- mer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal

Phyacs.

Mineral Products. Engineering Ceramics. Glass. Refiractories. Enameled Metals. Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer. Concreting Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. SEAC Engineering Group. Components and Techniques. Digital Circuitry.

Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures. BOULDER, COLORADO

Cryogeiiic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas liquefaction. Radio Propagation Physics. Upper Atmosphere Rese.arch. lono^heric Research. Regular Propagation

Services. Sun-Earth Relationships. VHF Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy and Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Research. Radio Noise. Tropospheric Measurements. Tropospheric Analysis. Propagation Obstacles Engineering, Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. High Frequency Impedance Standards. Electronic Calibration Center. Microwave Physics. Microwave Circuit Standards.

Radio Communication and Systems. Low Frequency and Very Low Frequency Research. High Fre- quency andVery High Frequency Research. Ultra High Frequency andSuper High Frequency Research. Modulation Research. Antenna Research. Navigation Systems. Systems Analysis. Field Operations.