NBS TECHNICAL NOTE 812

Tensile Behavior of

Boron/Epoxy-Reinforced

7075-T6 Aluminum Alloy

at Elevated Temperatures
NATIONAL BUREAU OF STANDARDS

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Tensile Behavior of Boron/Epoxy-Reinforced

7075-T6 Aluminum Alloy at Elevated Temperatures

National Bureau of Standsrdi

APR 2 9 1974 Daniel J. Chwirut '

and C r,

George F. Sushinsky i i IT

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D.C. 20234

Sponsored by the National Aeronautics and Space Administration Langley Research Center Hampton, \ irginia 23365

'*''*f>,uoV^'""

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued March 1974
National Bureau of Standards Technical Note 812

Nat. Bur. Stand. (U.S.), Tech. Note 812, 31 pages (Mar. 1974)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by llie Superiiiteiulent of Documents, U.S. Government Printing OHice, Washington, D.C. 20402 (Order by SD Catalog No. Ci:i.46:812). Price 65 cents.
CONTENTS

Page

1. INTRODUCTION 1

2. ANALYSIS 2

3. TEST SPECIMENS 4

3.1 Boron/Epoxy Specimens 4

3.2 Aluminum-Alloy Specimens 4

3.3 Sandwich Specimens 4

4. TEST EQUIPMENT 5

4.1 Testing Machine 5

4.2 Heating System 5

4.3 Strain Measurement 5

5. TEST PROCEDURE 5

6. EXPERIMENTAL RESULTS 6

6.1 Single Component Specimens 6

6.2 Sandwich Specimens 6

7. DISCUSSION 7 7.1 Load-Strain Behavior of Composite-Reinforced Metal 7 7.2 Correlation Between Experiment and Analysis 7 7.3 Effects of Specimen Volume Fraction 8

8. CONCLUSIONS 8

9. REFERENCES 9

APPENDIX 26

111

TENSILE BEHAVIOR OF BORON/EPOXY-REINFORCED 7075-T6

•ALUMINUM ALLOY AT ELEVATED TEMPERATURES

Daniel J. Chwirut and George F. Sushinsky

Static tensile tests were performed on specimens of 7075-T6 aluminum alloy, 0° unidirectional

boron/epoxy, and 7075-T6 aluminum alloy reinforced

on the surface with 0° unidirectional boron/epoxy

laminate, at four temperatures up to 300 °F (149 °C)

.

Analytical load-strain curves are formulated for the

reinf orced-metal specimens using the rule of

mixtures , assuming that the longitudinal strains

in the composite and the metal remain equal, and

taking account of the residual stresses caused by

the fabrication process. Two analytical curves are plotted for each reinf orced-metal specimen, one based on the measured ply thickness of the composite,

and one based on a nominal 0.005-in (0.13-mm) ply

thickness. In general, the experimental loadstrain curves fall between the two analytical curves

for each specimen.

Key words: Aluminum alloy; boron/epoxy; co-cure;

composite materials; fabrication process;

load-deformation characteristics; residual stress;

rule of mixtures; sandwich specimen; stress-strain

curves; tensile properties.

1. INTRODUCTION

One philosophy of structural design with advanced composite

materials involves the selective reinforcement of metallic components

with fiber-reinforced composite materials. The advantages of this

philosophy include large weight savings, minimal composite usage, and

retention of current joining and fastening technology. Several

experimental investigations of the benefits to be expected from using

composite materials in this way have been made [1-4]*.

Figures in brackets indicate literature reference on page 10.
Because of the difference in coefficients of thermal expansion for

the metal and composite, residual stresses are Introduced in the

components if the structure is used at a temperature other than the

temperature at which the structure is fabricated. Two commonly used

techniques for fabricating composite-reinforced metal structures are the

co-curing technique, by which the composite is cured and resin-bonded to

ttie metal in the same process, and the secondary bond process, by which

the composite laminate is first cured and then bonded to the metal using

another adhesive. For room temperature applications, significant

residual stresses can be introduced in the components fabricated by the

co-curing technique, whereas structures can be fabricated with

essentially no residual stresses if the secondary bond process is used

with a room temperature curing adhesive. For higher temperature

applications, the co-curing process may be preferable since the residual

stresses are relieved as the temperature approaches the curing

temperature for the composite. Several studies of the effects of these

residual stresses on the static and creep strengths of boron/epoxyreinforced metals have been made [5-7].

The investigation reported herein was undertaken to experimentally

determine the elevated temperature load-strain behavior of boron/epoxyreinforced 7075-T6 aluminum alloy fabricated by the co-curing process,

and to determine if this behavior can be predicted by a rule-of-mixtures

approach. Residual stresses resulting from fabrication are included in

the analysis, and various composite-to-metal volume ratios are considered. This investigation was performed in the Engineering

Mechanics Section of the National Bureau of Standards. Part of this

work was carried out under the sponsorship and with the financial

assistance of the National Aeronautics and Space Administration, Langley

Research Center.

2. ANALYSIS

The basic assumption of this analysis is that the total external

load applied to a composite-reinforced metal is distributed between the

component materials such that the strains in the direction of the

applied load are the same in both components. Using this assumption,

predictions of load-strain behavior and tensile moduli for compositereinforced metal specimens can be made if the stress-strain behaviors of

the component materials are known. Residual stresses resulting from

fabrication are accounted for by displacing the initial points on the

component material stress-strain curves an amount corresponding to the

component residual stresses.
The residual strains in the components were calculated using thermal

expansion coefficients of 2.8 x 10~^/°F** and 13.6 x 10-6/°F (5.0 x IQ-^

/ °C and 24.5 x 10~^/°C) for the boron/epoxy and aluminum alloy,

respectively. Assuming that the residual strains are elastic, it can be

shown that the residual strain in the aluminum alloy at any temperature

T is given by

e =

(a^ - a.) (To - T) a D a 1 ^ E A

1 + a a

E, \

where the a's are thermal expansion coefficients, the E's are the

tensile moduli in the direction of the residual strains, the A's are cross-sectional areas, and subscripts a and b denote aluminum alloy and

boron/epoxy, respectively. To is the stress-free temperature, which was taken to be 350 °F (177 °C) , the maximum tepiperature in the cure cycle.

In order to develop the load-strain curve for a reinf orced-metal

specimen, the increases in stresses for an incremental increase in

strain were determined for each component from the stress-strain curve

for that component. The starting point on the aluminum-alloy curve was taken to be the point corresponding to the calculated value of the

residual strain for that specimen. For the boron/epoxy, this correction

was unnecessary since the stress-strain curves for this material are essentially linear (see figures 6-9) . The component stresses for

successive strain increments were multiplied by the respective cross- sectional areas, added, and are plotted as a load-strain diagram.

Strain increments of 500 x 10~^ were used.

Using the scheme described above, two load-strain curves were

calculated for each specimen.- One was based on the actual measured

cross-sectional areas of the composite and the metal, and one was based

on a nominal 0.005-in (0.13-mm) ply thickness for the composite

laminate. This was done in order to eliminate variations in the elastic

modulus caused by slight variations in the fiber volume fraction of the

composite. In 0° unidirectional boron/epoxy, the load-carrying

capability (force) and the stiffness (force per unit deformation or strain) are essentially unaffected by slight variations in volume

fraction caused by bleeding out different amounts of resin during

**Units for physical quantities in this paper are given in both the U. S, Customary Units and the International System Units (SI) . Conversion factors

pertinent to the present investigation are presented in the Appendix.
the curing process, since the resin carries only a small percentage of

the total load. However, because of the area terms, the ultimate

strength (stress) and the elastic modulus (stress per unit strain) are affected. For small variations in volume fraction, the load-carrying

capability of a metal reinforced with 0° unidirectional boron/epoxy is

determined principally by the cross-sectional area of the metal and the

number of fibers. Therefore, it was felt that more consistent results

would be obtained if a normalized cross-sectional area based on a nominal ply thickness were used.

3. TEST SPECIMENS

The geometric configurations of the specimens tested in this

investigation are shown in figure 1,

3.1 Boron/Epoxy Specimens

The composite specimens were unidirectional boron/epoxy with the

filaments alined along the axis of loading. The material was purchased

as continuous prepreg tape and cured by the platen-press technique using

pressures and temperatures recommended by the manufacturer. The

material contained approximately 212 0.004-in (0.10-mm) diameter

filaments per inch (83 filaments per cm) of tape width. The material

was supplied with a glass scrim backing, 0.001 in (0.03 mm) thick. The

filament volume fractions of these specimens, as measured by the pointcounting technique, were between 54 and 58 percent.

3.2 Aluminum Alloy Specimens

Aluminum alloy specimens were cut from a single sheet of 0. 032-in

(0.8-mm) thick 7075-T6 aluminum alloy. All specimens were cut so that

the longitudinal axis of the specimen was in the direction of rolling of

the sheet. The specimen geometry was the standard flat tensile specimen

(fig. 6 of ASTM Designation E8-69 , Tension Testing of Metallic

Materials) , with a reduced section approximately 7 in (18 cm) long. All

specimens were preconditioned by a thermal treatment of one hour at 325

°F (163 °C) and five hours at 350 °F (177 °C) prior to testing. This

simulated the thermal treatment experienced by the aluminum alloy during

the co-cure processing of the sandwich specimens which is discussed

below.

3.3 Sandwich Specimens

Sandwich specimens consisting of 2, 4, 8, 10 or 12 plies of boron/

epoxy between two sheets of 0. 032-in (0.8-mm) thick 7075-T6 aluminum

alloy were tested. The specimens were fabricated by curing the

composite and resin-bonding it to the aluminum alloy in the same
operation without a supplementary adhesive. Good adhesion between

composite and aluminum alloy was achieved for test temperatures up

to 300 °F (149 °C) . Volume fractions for these specimens were not

measured, but based on specimen thicknesses the composite was judged

to be approximately 40 percent filaments and 60 percent epoxy.

4. TEST EQUIPMENT

4.1 Testing Machine

The test program was conducted in a screw-powered universal testing

machine. The calibration of this machine was verified in accordance

with ASTM Designation E4-64, Standard Methods of Verification of Testing

Machines. Errors in applied loads were less than one percent. Specimen

alinement was enhanced by the use of spherical seats in the load train.

4.2 Heating System

The test furnace is composed of two semi-cylindrical sections hinged

along one side. The walls of the furnace were fabricated from 0.5-in

(1-cm) thick asbestos cement pipe, while the upper and lower cover plates are of 1-in (2-cm) thick asbestos cement sheet.

Heat is supplied by three semi-cylindrical radiant heating units in

each half of the furnace. The annular space between the heating units

and the outer shell is packed with glass fiber insulation. The heaters

are wired in pairs, and the power to each pair is regulated separately.

Temperature was measured with two thermocouples taped to opposite sides

of the specimen equally spaced above and below the mid-height of the

specimen. Temperature was controlled and recorded by a timeproportioning, recording controller.

4.3 Strain Measurement

Each specimen was instrumented with two electrical resistance strain

gages mounted back-to-back, and alined along the longitudinal axis. The

gages were connected in series to record the average strain.

5. TEST PROCEDURE

The same procedures were followed for tests on all three types of

specimens. The specimen was cleaned with acetone to remove dirt and

oil. Strain gages were bonded to the specimen using an epoxy adhesive,

and thermocouples were taped to the specimen, which was then mounted in

the testing machine.
The specimen was heated to the test temperature in approximately 20

minutes. Adjustments were made to the temperature controller and power

regulators to reduce the temperature variations to an acceptable level.

A difference of 3° F (2 °C) or less between thermocouples and a time

variation of 2 °F (1 °C) over the duration of the test were considered

acceptable. The specimen was maintained at this condition for 30

minutes prior to the application of the load.

Strain readings were taken at discrete load levels up to specimen

failure, while temperature was continuously recorded for the duration of

the test.

6. EXPERIMENTAL RESULTS

6.1 Single Component Specimens

Tensile tests at four temperatures were performed on boron/epoxy

specimens and on aluminum alloy specimens to obtain stress-strain

curves. Initial tangent tensile moduli were determined in accordance

with the procedure outlined in ASTM Designation E231-69, Static

Determination of Young's Modulus of Metals at Low and Elevated

Temperatures, except that resistance strain gages were used instead of

extensometers. The moduli determined from these tests are given in

table 1. Stress-strain curves for the aluminum alloy were faired

through the data from two tests at each temperature. These curves are given in figures 2 through 5. Stress-strain curves for the boron/epoxy

specimens, based on actual measured area and based on a nominal 0.005-in

(0.13-mm) ply thickness, are given in figures 6 through 9.

6.2 Sandwich Specimens

Tensile tests on sandwich specimens with four plies of boron/epoxy

between two sheets of 7075-T6 aluminum alloy were performed at four

temperatures. The test conditions and results are given in table 2.

Tensile tests on sandwich specimens with 2, 4, 8, 10, and 12 plies

of boron/epoxy were performed at 150 °F (66 °G) to determine the effect

of composite-to-metal volume ratio. Tests conditions and results of

these tests are given in table 3.

Load-strain curves for the 4 - ply specimens are shown in figures 10

through 17 while the family of curves for the 2, 4, 8, 10, and 12 ply

specimens is shown in figure 18.

The experimental and the calculated initial tangent tensile moduli

for each specimen were determined graphically from the experimental and

calculated load-strain curves for that specimen. These moduli are given
in tables 2 and 3. The experimental elastic moduli for specimens with

different amounts of boron/epoxy reinforcement are shown as a function

of specimen volume fraction in figure 19.

Most tests resulted in failure of the boron/epoxy in the grips,

followed by aluminum failure or gross debonding. Therefore, no meaningful ultimate strength data were obtained.

7. DISCUSSION

7.1 Load-Strain Behavior of Composite-Reinforced Metal

The load-strain curves for the boron/epoxy-reinforced 7075-T6

aluminum alloy specimens tested in this investigation are generally

nonlinear from zero load, with the amount of nonlinearity decreasing

with increasing temperature. This nonlinearity is expected since these curves are combinations of the essentially linear, boron/epoxy stressstrain curves (figs. 6-9) and the nonlinear aluminum alloy stressstrain curves (figs. 2-5). Herakovich [5, 6] has reported the loadstrain curves for boron/epoxy-reinforced aluminum and titanium to be

basically bilinear at room temperature. His stress-strain curves appear

to be strictly linear for boron/epoxy and bilinear for aluminum and

titanium (see [6], fig. 6). The differences between the stress-strain

behaviors of the aluminum alloy specimens reported by Herakovich and

those tested in this investigation may by due to differences in the

thermal preconditioning prior to testing.

7.2 Correlation Between Experiment and Analysis

For tests run at the three lowest temperatures, the experimental

load-strain curves generally fall between the two analytical curves

(figs. 10-15). For both tests at 300 °F (149 °C) the experimental

curves fell below both analytical curves (figs. 16-17). This trend also occurs in the moduli data (table 2) . The differences between the

calculated moduli and the experimentally determined moduli range from

to 20 percent of the experimental moduli.

Two factors contributing to these discrepancies are differences in

the volume fractions of the boron/epoxy between component specimens and

sandwich specimens, and uncertainty in the values of residual stress in

the specimen. The influence of the first factor may be removed by using

the normalized ply thickness. Although this did not remove the

discrepancies completely, the normalized- thickness curves are somewhat

closer to the experimental curves than the curves based on the actual

measured areas. It appears then that uncertainty in the residual stress

is the prominent factor. An earlier investigation at this laboratory

[7] indicated a large scatter in the values of residual stress measured
in specimens fabricated using the co-cure method. If the exact value of

residual stress were determined for each specimen, analytical results

more consistent with the experimental results might have been obtained.

7.3 Effects of Specimen Volume Fraction

With no residual stresses, the tensile modulus of the reinforcedmetal specimens would be expected to increase linearly with increased

reinforcement (see dashed line, fig. 19), based on a simple rule-ofmixtures combination of the tensile moduli of the two component

materials. When residual stresses are considered, the effective tensile

modulus of the metal is reduced, and the modulus of the reinforced metal

is somewhat below the linear relationship. The overall effect of the

reduction in metal modulus is lessened as the volume fraction of metal

in a reinf orced-metal specimen is reduced. The limiting value is the

modulus of the composite at 100 percent composite volume fraction. This

trend is followed closely by the experimental data as shown in figure

19.

8. CONCLUSIONS

Based on the experiments and analysis covered by this report, the

following conclusions are drawn:

1. Load-strain curves for 7075-T6 aluminum alloy

reinforced with 0° unidirectional boron/epoxy

at temperatures up to 300 °F (149 °C) can be

formulated with reasonable accuracy from stressstrain data on the component materials. The

analysis, which is based on an empirical ruleof-mixtures approach, includes a prediction of

the effect of the fabrication residual stresses

in the component materials.

2. If a normalized area, based on a nominal 0.005-in

(0.13-mm) ply thickness, is used for the com- posite, the resulting analytical load-strain

curves are generally closer to the experimental

curves than the curves based on actual measured

cross-sectional areas. This normalization

removes the effect of small changes in the

amount of epoxy matrix in the system which add

negligible strength or stiffness to a compositereinforced metal.

3. The discrepancies between the analytical and the

experimental load-strain curves probably result

from inaccuracies in the values of residual stress
used in the calculations.

4. The elastic modulus of boron/epoxy-reinforced

7075-T6 aluminum alloy fabricated by co-curing

increases nonlinearly with increased amounts of

reinforcement. This nonlinearity results from

the fabrication residual stresses, which reduce

the effective modulus of the metal component.

9. REFERENCES

[1] Zender, G. W. and Dexter, H. B. , Compressive Properties and Column

Efficiency of Metals Reinforced on the Jurface with Bonded Filaments,

NASA TN D-4878, (1968)

.

[2] Dexter, H. B. , Compressive and Column Strengths of Aluminum Tubing

with Various Amounts of Uni-directional Boron/Epoxy Reinforcement,

NASA TN D-5938, (1970).

[3] Marlowe, D. E. , Torsional Instabilities in Composite-Reinforced

Aluminum-Alloy Thin-Walled Cylinders, NBS TN 728, (1972).

[4] Mitchell, R. A., Woolley, R. M. , and Chwirut , D. J., Composite-Overlay

Reinforcement of Cutouts and Cracks in Metal Sheet, NBSIR 73-201

(February 1973)

.

[5] Herakovich, C. T. , Tensile Strength Behavior of Composite Reinforced

Metals, Phase I Report: Boron/Epoxy Reinforced Metals, Virginia

Polytechnic Institute and State University Report VPI-E-72-11, (1972).

[6] Herakovich, C. T. , and Brooks, E. W. , Jr., Tensile Strength Behavior

of Composite Reinforced Metals, Virginia Polytechnic Institute and

State University Report VPI-E-73-5, (1973).

[7] Chwirut, D. J., Tensile Creep of Boron/Epoxy and Boron/Epoxy-Reinforced

7075-T6 Aluminum Alloy, NBS TN 722, (1972).
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AVERAGE STRAIN

FIGURE 2. STRESS-STRAIN CURVE FOR PRECONDITIONED

7075-T6 ALUMINUM ALLOY AT 75°F(24°C)

10 ITxTtr^

70x10^

60

CO

CO

UJ SPECIMENS A3, A4

T = 150°F

4 5 6

AVERAGE STRAIN

10 11x10-^

FIGURE 3. STRESS-STRAIN CURVE FOR PRECONDITIONED

7075-T6 ALUMINUM ALLOY AT 150°F(66°C)

14
60x10

SPECIMENS A5, A6

T - 225°

F

2 3 4 5 6 7

AVERAGE STRAIN

FIGURE 4. STRESS-STRAIN CURVE FOR PRECONDITIONED

7075-T6 ALUMINUM ALLOY AT 225°F{107°C)

9x10-3

60x10^

50

SPECIMEN A46

T = 300°

F

FIGURE 5. STRESS-STRAIN CURVE FOR PRECONDITIONED

7075-T6 ALUMINUM ALLOY AT 300°F{149°C)

9x10-3

15
uX

tAoozoaUl

CO<<Ul<

•—U<Zo<

o"<u

a.COOQ.oeeO

CA>I (A

(A

(O

UJ

oe

Zi

zui/iqi 'ssaais

16
ec

UcaLU

CO< o^" O o CM CMN zU!/wi ssaais o

CO

tnZ111 oUJOa.

UJZoecOOu.

CO

UJ>ccO

c/)I CO

CO

Ul

UJ

cc

C5

jUi/jqi 'SSHHiS

17
a:O

jU!/»qi ssaais

«I r*

cc

m

t- o T~ CO C3

u. o

iii OJ z Cv4 o •—< aUJ CO to <z < UJ OQ fe ..0 UJ

0.

CO

>-X

OlUJ

^^2CccCO

ce 1 1 1 -' ""T 1 1 1 1 1 - - -

CO - - CO ^^s. ~ - -^V - - \ - - 1 1 1 I 1 1 1 1 1 X

Z3Z<oc

I—CO < CO

CO

UJ III cc oc < »— —J CO < . z r) 00 < 1X1 oc

H- < -3

CO z u

u.

aLU

CO<OQ

Csl

O

CO o o o

CM

Oo o

CO oo o o

cs

^ui/iqi 'SS2aiS

18
n

I o

^ lO

o

O

LU UJ 5 >

u

sr O <

r» < cc

t— < ?» CO

OC»— O 1 c> CO CO u LU

UJ CC CO 1— < CO

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^ui/jqi 'SS3U1S

19
5.0x10^

4.5

4.0

3.5 S 3.0 Q 2.5 o

-• 2.0 —- "Experimental

.Calculated, actual area

Calculated, 0.005 in/ply thickness

4

STRAIN

8 9x10-3

FIGURE 10. EXPERIMENTAL AND CALCULATED LOAD-STRAIN RELATIONS FOR

SPECIMEN BA-1 (T = 75°F, 24°C)

Expertmental

Calculated, actual area Calculated, 0.005 in/ply thickness

STRAIN

8x10-3

FIGURE 11. EXPERIMENTAL AND CALCULATED LOAD-STRAIN RELATIONS FOR

SPECIMEN BA~2 (T = 75°F, 24°C)

20
___ Experimental

Calculated, actual area Calculated. 0.005 ply thickness

8x10-^

STRAIN

FIGURE 12. EXPERIMENTAL AND CALCULATED LOAD-STRAIN RELATIONS FOR

SPECIMEN BA-4 {T ^ 150°F. 66°C)

Experimental

n Calculated, actual ares :- Calculated, 0.005 ply

thickness

8x10-3

STRAIN

FIGURE 13. EXPERIMENTAL AND CALCULATED LOAD-STRAIN RELATIONS FOR

SPECIMEN BA-11 (T - 150°F, 66°C)

21
Experimental

Calculated, actual area

Calculated, 0.005 ply thtckivess

7x10-^

STRAIN

FIGURE 14. EXPERIMENTAL AND CALCULATED LOAO-STRAIN RELATIONS FOR

SPECIMEN BA-5 (T = 225°F, 107°C)

4.0x10^,

-ZP-

- Experimental - Calculated, actual area - Calculated, 0.005 ply thickness

3

STRAIN

7x10-3

FIGURE 15. EXPERIMENTAL AND CALCULATED LOAD-STRAIN RELATIONS FOR

SPECIMEN BA-6 (T = 225° F, 107°C)

22
3 4 5 6x10"

STRAIN

FIGURE 16. EXPERIMENTAL AND CALCULATED LOAD-STRAIN RELATIONS FOR

SPECIMEN BA-7 (T = 300" F. 149°C)

4.0x10?

o — Experimental

Calculated, actual area Calculated, 0.005 ply -

thickirass

6x10-3

STRAIN

FIGURE 17. EXPERIMENTAL AND CALUCLATED LOAD-STRAIN RELATIONS FOR

SPECIMEN BA-8 (T = 300° F, 149°C)

23
8x10z2

STRAIN

8x10-3

FIGURE 18. EXPERIICNTAL LOAD-STRAIN CURVES FOR BORON/EPOXY REINFORCED PRECONDITIONED

7075-TI ALUIIINUM ALLOT WITH DIFFERENT VOLUM FRACTIONS AT 150°F(66°C)

24
*/ ---. Linear approximation

f / —.^^ Analysis *' O Experiment

_L

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 VOLUME FRACTION COMPOSITE

FIGURE 19. TENSILE MODULUS AT 150°F(66°C) FOR RECONDITIONED 7075-T6 ALUMINUM ALLOY

REINFORCED WITH VARIOUS AMOUNTS OF BORON/EPOXY

25
APPENDIX

Conversion of U. S. Customary Units to SI Units

For simplicity, only U. S. customary units have been used in the

figures of this report. It should be noted that the U.S.A. is a signatory to the General Conference of Weights and Measures which gave

official status to the metric SI system of units in 1960. Conversion

factors for units used in this paper are given in the following table:

Physical U. S. customary

quantity unit SI unit Conversion factor

Force pound-force (Ibf) newton (N) 1 Ibf = 4. 448 N

Length inch (in) metre (m) 1 in = 0.0254 m

Area in^ m^ 1 in^ = 6.4516 x 10"^ m^

Stress Ibf/in^ N/m^ 1 Ibf/in^ = 6895 N/m^

Temperature °F °C °C - 0.556 (°F - 32)

Other conversion factors can be found in ASTM Standard Metric Practice

Guide, ASTM Designation E380-72 (available from American Society for

Testing and Materials, 1916 Race Street, Philadelphia, Pennsylvania

19103).

26
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MHIK A I ION OK KI-,l'OI< I NO. NBS TN-8L22. t.o' NoAtu, 3. Kii ipu-ni's All.xssidn No.

4. rni.i-; and si:ni i ii r Tensile Behavior of Boron/Epoxy - Reinforced 7075-T6

Aluminum Alloy at Elevated Temperatures.

5. I'ubliciiion n.itr March 1974

6. I'lTftirmin^ Orj^.niixai uiii < oJi

7. AT mOK(S)

Daniel J. Chwirut and George F. Sushinsky

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16. .\H,S1KA( I (A 200-\vord or less factual summary of most ,sign/7(can( information. If document includes a >:i^nificant bibliography or literature survey, mention it here.)

Static tensile tests were performed on specimens of 7075-T6 aluminum alloy,

0° unidirectional boron/epoxy, and 7075-T6 aluminum alloy reinforced on the surface

with 0° unidirectional boron/epoxy laminate, at four temperatures up to 300 °F

(149 °C). Analytical load-strain curves are formulated for the reinf orced-metal

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composite and the metal remain equal, and taking account of the residual stresses

caused by the fabrication process. Two analytical curves are plotted for each

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17. K\-.Y WIORHS (si\ to twelve entries- alphabetical order; capitalize only the first letter of the first key word unless a proper name: separated by semicolons) Aluminum alloy; boron/epoxy; co-cure; composite materials;

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