NATL INST. OF STAND & TECH R.I.C.

A111D4

NATIONAL INSTITUTE OF STANDARDS &

TECHNOLOGY

Research Information Center

Gaithersburg, MD 20699

United States Department of Commerce

National Institute of Standards and Technology

N/STIR 3986

ALUMINUM-LITHIUM ALLOYS:

SURFACE-CRACKED TENSION FRACTURE TESTS

AND PHYSICAL AND THERMAL PROPERTIES AT

CRYOGENIC TEMPERATURES

P.T. Purtscher

M. Austin

S. Kim

D. Rule

NISTIR 3986

ALUMINUM-LITHIUM ALLOYS:

SURFACE-CRACKED TENSION FRACTURE TESTS

AND PHYSICAL AND THERMAL PROPERTIES AT

CRYOGENIC TEMPERATURES

P.T. Purtscher

M. Austin

S. Kim

D. Rule

Materials Reliability Division

Materials Science and Engineering Laboratory

National Institute of Standards and Technology

Boulder, Colorado 80303

March 1992

Prepared for:

Air Force Systems Command

Astronautics Laboratory

Edwards Air Force Base, CA 93523-5000

U.S. DEPARTMENT OF COMMERCE, Barbara H. Franklin, Secretary

TECHNOLOGY ADMINISTRATION, Robert M. White, Under Secretary for Technology

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, John W. Lyons, Director

CONTENTS

Page

INTRODUCTION 1

Section 1—SURFACE FLAW FRACTURE TESTING 3

Materials and Procedures 3

Results 9

Discussion 16

Conclusions 27

Section 2—ELASTIC PROPERTIES 28

Elastic-constant Measurement Methods 28

Results 28

Discussion and Summary 30

Section 3 —THERMAL EXPANSION 32

Materials and Measurement Methods 32

Results 32

Discussion and Summary 32

Section 4—THERMAL CONDUCTIVITY 40

Apparatus 40

Experimental Procedure ..... 41

Computation of Thermal Conductivity 42

Results 42

Thermal Conductivity of Alloy X2095 (4%Cu-l%Li) 42

Accuracy and Reproducibility of Measurements

for Moderate Conducting Material 48

OVERALL SUMMARY 49

ACKNOWLEDGEMENTS 49

REFERENCES 49

APPENDIX A: TABLES OF PHYSICAL PROPERTIES AS A FUNCTION

OF TEMPERATURE 51

APPENDIX B: TABLES OF THERMAL EXPANSION DATA AS A FUNCTION

OF TEMPERATURE 59

iii
ABSTRACT

Surface-cracked tension fracture tests were conducted in the T-S orientation at

295, 76, and 4 K on two plate alloys (X2095-T851, plate thickness of 12.7 mm and

2090—T81, plate thicknesses of 12.7 and 19.1 mm). The cryogenic toughness to

room temperature toughness ratio for alloy 2090 is generally higher than that

found for alloy X2095. Both alloys have significantly lower tensile properties

near the surface of rolled plate than in the center of the plate.

The physical properties of seven plate specimens were measured from liquid helium

to room temperature. Three variations in chemical composition of alloy X2095,

three different samples of alloy 2090, and a single sample of alloy 2219-T87 were

included. The mass density of Al alloys decreases by 4% / mass % of Li. The

influence of texture on elastic properties is considered minimal because there

is less than 5% variation in elastic-stiffness in the Al-Li alloys. The shear

and Young's moduli increase 3 to 4% / mass % Li. The bulk modulus and Poisson

ratio decrease by 3% / mass % Li.

Thermal expansion between 4 and 320 K was measured on the same seven plate

specimens included in the physical properties study. All of the materials showed

a typical temperature dependence where the slope of the coefficient of thermal

expansion (CTE) vs. temperature curve has a zero slope near absolute zero and a smooth monotonic increase to a constant slope near room temperature.

The thermal conductivity of alloy X2095 (4%Cu-l%Li) was determined over the

temperature range 4.2 to 300 K using a steady-state apparatus. The conductivity

at 290 K was approximately 40% higher than at 77 K and was 37 times that at

4.6 K. The thermal conductivity of alloy X2095 is approximately twice that of

alloy 2090, previously measured in the same apparatus. Compared to that of a published literature value for alloy 2219, the thermal conductivity of alloy

X2095 is about 65% lower than for alloy 2219.

Keywords: aluminum-lithium alloys; cryogenic properties; elastic properties;

fracture toughness; residual strength; thermal conductivity; thermal expansion

iv
INTRODUCTION

The use of aluminum- lithium (Al-Li) alloys in this country has been hampered

by the lack of engineering data, particularly at cryogenic temperatures [1].

Selected cryogenic mechanical properties of various high-strength Al-Li alloys

have previously been measured and reported [2]. This report covers additional

testing of Al-Li plates: (1) fracture tests of surface - cracked tension (SCT)

panels, (2) measurement of physical properties including the elastic constants,

mass densities and the elastic stiffness (a measure of texture), (3) thermal

expansion, and (4) thermal conductivity. Measurement of specific heat will be

performed by an outside contractor and will be included in a separate report.

The test matrix is shown in Table 1. The chemical composition of the alloys

is shown in Table 2.

All of the materials are 12.7 mm (0.5 in) thick with the exception of one

plate of 2090 that is 19.1 mm (0.75 in) thick. Duplicate tests were run for

elastic properties and thermal expansion from the center (19.1 mm thick-C) and

from the near surface area (19.1 mm thick-S) of the thickest plate. Alloy 2219

is included as a baseline material that contains no Li.

This program is sponsored by the Air Force Systems Command, Phillips

Laboratory, Edwards Air Force Base. It is part of the Materials and Processes

Validation (3101) of the Structures, Materials, and Manufacturing ( 3000 ) portion of the Advanced Development Program for the National Launch System

(NLS) . The report is broken down into four separate sections that cover each

type of test.

1
Table 1. Test matrix for report.

material

elastic

properties

thermal

expansion

specific

heat

SCT

fracture

conduc

tivity

2090 12.7 mm X X X

2090-C 19.1 mm X X X

2090-S 19.1 mm X X X

X2095 lot 1 X X

X2095 lot 2 X X X

X2095 lot 3 X X X X

2219 X X

Table 2. Chemical compositions of Al-Li and 2219 alloy plates.

Alloy Cu Li Mg Zr Si Fe ; ?i Ag J'i; Hi ;

2090

12.7 mm

2.70 2.30 0.03 0.12 0.08 0.19 0.01

2090

19 . 1 mm

2.85 2.30 0.05 0.10 0.07 0.13 0.01

X2095 - lot 14.72 1.28 0.42 0.12 0.02 0.03 0.02 0.35 0.01

X2095 - lot 2

4.36 1.25 0.39 0.14 0.03 0.07 0.02 0.35 <0.01

X2095 - lot 3

4.08 1.01 0.35 0.13 0.03 0.03 0.03 0.35 —

2219 5.71 — <0.0 0.15 0.07 0.02 0.03 — <0.00

2
Section 1 SURFACE FLAW FRACTURE TESTING

Materials and Procedures

Three different Al-Li alloy plates were tested in this part of the

program, X2095-T851 at a thickness of 12.7 mm (referred to as X2095) and

2090-T81 at two thicknesses of 12.7 and 19.1 mm (referred to as 2090-1/2 and

2090-3/4). These plates were part of an earlier test program and the

initial characterization of the as-received plates can be found elsewhere

[2], The plate of X2095 used was previously identified as WL049-T851 lot 2,

which contains 4.4% Cu and 1.3% Li.* Pertinent properties are summarized in

Table 3. Data for alloy 2219-T87, currently used for the external tank of

the space shuttle, are shown also for comparison. Fracture toughness

(KIc (J)) decreased as the strength of the alloys went up. Alloy X2095 has

the highest strength, but the lowest toughness of the three plates. The

2090-1/2 plate has a lowest strength, but the highest toughness, and properties of the 2090-3/4 plate are between the two extremes. Alloy 2219 has

lower strength than the Al-Li alloys, and toughness and strength increase

with decreasing temperature.

Table 3. Summary of previously reported mechanical

properties (transverse orientation.

Alloy & Temp. MPa MPa

El.,

%

R.A . , % MPa - Jm

2090-1/2-295 K 507 546 2 4 32

- 76 K 570 610 1 4 39 |

- 4 K 621 669 1 4 46

2090-3/4-295 K 559 597 6 13 25

- 76 K 624 693 3 4 24

- 4 K 670 760 3 4 38

X2095 - 295 K 590 633 10 27 22

- 76K 680 760 9 15 22

- 4 K 775 853 9 14 22

2219 - 295 K 381 472 13 28 27

- 76 K 456 582 13 24 36

- 4 K 499 701 14 22 36

Trade names are furnished to identify the materials and do not imple

recommendation of endorsement by NIST.

3
Table 4 shows the initial plan for the SCT tests. The test program was

designed so that the effects of material gage, specimen thickness (t) , test

temperature, flaw width (2c) and flaw depth (a) were examined. Stage 1

would look at the effect of temperature and material gage. Stage 2 would

study the effects of temperature and flaw shape. Stage 3 would look at

specimen thickness and test temperature. The starting plan was to obtain

6.4 mm thick sheets of both alloys 2090 and X2095 to test along with the

12.7 mm thick plates that were already on hand. The 6.4 mm thick sheets of

alloys 2090 and X2095 could not be procured and additional tests on the

materials already in hand were added to the program to finish in a timely

fashion

.

Table 4. Test matrix for SCT tests for X2095 and 2090.

STAGE 295 K 76 K 4 K

I — t=3 . 2 mm,

a/c=0.25, a/t=0.7

2 from plate

2 from sheet

2 from plate

2 from sheet

2 from plate

2 from sheet

II — t=3 . 2 mm,

a/c=0.4, a/t=0.4

4 from plate 4 from plate none

III —• t=2 . 2 mm, 3 from plate 3 from plate none

The SCT fracture tests were conducted because the most likely mode of

failure is the propogation of a crack through the thickness of the fuel

tank. Previous tests [2] had characterized the in-plane orientations of the

plate, but not the through- thickness orientation. All of the ADP participants attended a workshop held in Boulder, Colorado on July 31, 1990 and

agreed that SCT tests were the most relevant to the design of the fuel

tanks. The T-S orientation was chosen because it would give lower values

than the L-S orientation.

The tests were conducted according to ASTM E 740-88 [3] for determining

the residual strength of SCT specimens. Full- thickness , dog-bone shaped

specimens were fatigue precracked at room temperature in three -point bending

with a frequency of 25 to 35 Hz. A span of 127 mm was used for the bend

fixture. Either electro-discharge machined slots or 0.60 mm diameter holes

were used as starter notches for fatigue precracking. The precracking load

varied from 17-2.5 kN for the 12.7 mm thick specimens to 45-4.5 kN for the

19 . 1 mm thick samples.

The supplemental analysis for fracture toughness is described in

appendix X3 . 2 of ASTM E 740. The method uses the original crack dimensions

to calculate the stress concentration factor and the residual strength as

the critical load. The procedure is appropriate for low- toughness materials, where crack- tip plastic zones are small and stable crack growth prior

to failure is absent. In all other cases, the fracture toughness analysis

4
is questionable and may lead to significant variations in toughness as the

specimen and flaw dimensions change. In the test plan, stage 1 was designed

so that the flaw and specimen dimensions would produce a valid toughness.

The variations in flaw and specimen dimensions in stages 2 and 3 were such

that a valid toughness may not be obtained. All of the data can be analyzed

according to the empirical method described in section X3.4 of E 740,

residual strength plotted against flaw size normalized to take into account

the width of the crack and the thickness of the plate.

After a suitable fatigue crack was obtained, the specimens were machined to the test thickness over the complete gage length. The specimens

were numbered so that the first digit refers to the stage of the test

program, followed by a hyphen and a specimen number, see Table 5. Some

specimens were machined from both sides so that the test section came from

the center of the plate (these specimens have an * following the specimen

identification) , but most of the specimens were machined from one side so that the test section came from the near surface region of the plate.

Figure 1 shows a schematic diagram that defines the various dimensions of

the specimens. Figure 2 shows schematic diagram of the machining done after

fatigue precracking to produce the final specimen dimensions for testing.

Flat tensile specimens (4 mm wide, 28 mm gage length, and with the same

thickness as the SCT specimen) were taken from the gage section of the SCT

specimen after SCT testing. Figure 3 is a schematic diagram illustrating

the relative location of the tensile specimens in the SCT specimen. Tensile

tests were performed at a constant cross -head rate of 0.05 cm/min.

The fracture surfaces of selected SCT specimens were observed in a scanning electron microscope (SEM) to document the failure mechanisms. The

fracture surface observations are used to characterize the state of stress

across the specimen thickness. Slant fracture, referred to as shear lips,

is related to a state of plane stress while a flat fracture relates to plane

strain. In the previous report [2]

,

the superior toughness of alloy 2090-

1/2 was attributed to numerous, large delaminations on the fracture surface

that produced a state of plane stress. Alloy X2095 exhibited a flat fracture with few, small delaminations at cryogenic temperatures. The low

toughness of alloy X2095 was then related to the stress state (plane strain)

and the lack of delaminations on the fracture surface.

5
Fig. 1. Schematic diagram showing the dog-bone shaped specimen

for the SCT test and all pertinent dimensions. For

these tests, L is 200 mm and W is 100 mm. The length

of the specimens, including the grips, is 450 mm.

6
7 Fig.

2.

Schematic

diagram

that

shows

the

region

of

the

specimen's

cross

section

that

was

machined

out

after

fatigue

precracking

(cross-hatched

area)

to

produce

the

final

thickness

of

the

test

specimen:

(a)

machined

from

center

of

plate

and

(b)

machined

from

surface

of

plate.

The

fatigue

precrack

is

represented

by

the

fine

dots.
Fig. 3. Location where small, flat tension specimens were

taken from the gage section of SCT specimen after SCT

test

.

8
Results

The SCT test results for alloy X2095 are summarized in Table 5. For

alloys 2090-1/2 and -3/4, the results are shown in Tables 6 and 7. The

specimen and flaw dimensions (a, t, and 2c) vary significantly as required in

the test plan. The M/$ and S values, the effective stress concentration factors, are defined in ASTM E 740. The residual strength (ct r ) , thickness (t),

and a/<£2 are the most significant columns to consider.

The term a/($2 -t) normalizes the data with respect to both the specimen

thickness and flaw shape. A plot of residual strength for alloy X2095 vs. the

normalized flaw size is shown in Fig. 4. The data at 295 K follow a trend

where the residual strength decreases in a linear fashion as a/($2 -t) increases. The data from stage 3 specimens, the thinnest specimens, fit the same

trend as observed for stages 1 and 2. Two of these specimens were machined

from the center and the others were machined from one side of the plate.

At 76 K, the data for alloy X2095 is generally lower than at 295 K (Fig.

4). For small flaws, a/($2 -t) - 0.28, there is large scatter. This variation

is due to a change in fracture mechanism from plane a for a shallow, wide

crack to plane e for a deeper, narrower crack. The observations that support

this explanation are discussed later. The data at 4 K is limited, but the

residual strength for a given flaw size appears higher than at 76 K, and about

equal to the residual strength at 295 K.

The data for alloy 2090 from the two plates at 295, 76, and 4 K are

plotted in Fig. 5. In general, the data for the two plates of 2090 at a given

temperature are comparable. At a given flaw size, the 76 -K residual strength

is higher than the 295-K strength. The 4-K data are slightly higher than data

at 76 K.

The tensile properties of SCT specimens are shown in Tables 8, 9, and

10. For alloy X2095 (Table 8), the flat tensiles taken from the mid- thickness

of the plate have nearly the same strengths as the round specimens tested

previously (shown in Table 3). The strengths at 76 K from flat tensiles

measured near the surface are about 20% lower than in the mid- thickness of

plates

For alloy 2090-1/2 (Table 9), the flat tensiles taken from the midthickness of the plate were slightly stronger than the comparable round

tensiles tested previously (Table 3). The strengths at 76 K of flat tensiles

from the surface were about 12% lower than the properties of flat tensiles

from the mid- thickness of the plate. For alloy 2090-3/4 (Table 10), flat tensiles machined from the surface of the plate exhibited 10 to 15% lower

strengths than found in round specimens machined from the mid- thickness of the

plates (Table 3). The tensile ductilities of all the flat tensiles from alloy

2090 were extremely low.

9
Table 5. Summary of SCT panels tests on alloy X2095 (WL049)

.

spec . #

a (mm)

t

(mm)

2c

(mm)

M/$ a/$ 2 (mm)

S

(MPa)

Ki.

(MPa

•

Jm)

tested at 295 K

1-3 1.92 3.23 22.6 1.64 2.21 0.50 352 44

1-12 1.72 3.36 16.4 1.42 1.77 0.55 449 47

2-5 1.77 3.18 5.23 0.89 1.00 1.00 524 ...

2-8 2.05 3.21 6.97 1.00 1.28 0.95 476 —

2-12 1.51 3.41 6.85 1.06 1.10 0.78 504 ...

3-1 0.95 2.36 4.05 1.01 0.67 0.79 518 ...

3-4 2.44 3.26 8.28 1.03 1.51 0.99 449 ...

3-29 0.95 2.51 3.79 1.10 0.86 0.85 495 ...

3-5 2.13 2.87 10.8 1.30 1.62 0.81 384 —

tested at 76 K

1-11 1.77 3.33 17.6 1.45 1.56 0.53 387 41

1-4 2.36 3.28 26.1 1.81 2.18 0.54 276 43

2-1 2.49 3.10 4.28 0.63 0.87 1.42 407 —

2-3 3.08 3.56 6.72 0.77 1.36 1.33 345 —

2-4 2.87 3.56 5.54 0.70 1.13 1.38 435 —

2-7 2.26 3.15 6.15 0.88 1.21 1.08 393 —

2-9 1.79 3.18 7.46 1.07 1.26 0.84 400 —

2-10 1.59 3.13 7.26 1.08 1.15 0.78 455 —

2-11 | 1.23 3.21 5.51 1.01 0.90 0.77 607 —

3-3 2.46 2.81 10.0 1.19 1.69 0.96 340 —

3-2 2.13 2.36 6.41 0.98 1.23 1.13 345 —

3-30 1.23 2.05 5.15 0.98 0.65 0.81 418 —

tested at 4 R

1-10 2.13 3.41 20.9 1.59 1.92 0.56 317 42

1-13 1.33 2.95 16.7 | 1.44 1.26 0.47 ! 531 50

10
Table 6. Summary of SCT panels tests on alloy 2090-1/2.

spec.# a (mm)t

(mm)

2c

(ram)

M/$ a/$ 2 (mm)

S (MPa)

Ki.

(MPa • ./m)

tested at 295 K

1-1* 2.51 3.49 21.2 1.61 2.21 0.62 338 48

2-31 0.82 3.23 19.2 1.28 0.80 0.33 386

1-35 2.59 3.13 15.0 1.48 2.10 0.77 352 47

1-15* 2.03 3.18 16.3 1.49 1.77 0.62 345 41

tested at 76 K

1-5* 1.51 3.26 13.5 1.34 1.36 0.55 449 41

1-14* 1.31 3.26 22.7 1.46 1.26 0.55 400 37

1-33 2.31 3.15 18.0 1.57 2.00 0.65 381 51

2-32 1.49 3.08 7.82 1.14 1.15 0.73 446

2-2 2.08 3.46 4.95 0.79 1.00 1.12 455+

tested at 4 K

1-9* 1.77 3.54 10.1 1.19 1.41 0.70 545 48

1-34 1.46 3.13 15.0 1.39 1.33 0.52 512 48

1-16* 1.72 3.13 20.3 1.57 1.59 0.50 518 59

11
Table 7. Summary of SCT panels tests on alloy 2090-3/4.

spec .

#

a (mm)

t

(mm)

2c

(mm)

M/$ a/$ 2 (mm)

S aR (MPa)

Kle

(MPa • /m)

tested at 295 K

2-13 0.62 3.18 11.1 1.18 0.59 0.37 501 26

2-14 1.21 3.38 10.9 1.23 1.07 0.54 378 29

2-19 1.18 3.18 3.38 0.84 0.65 0.96 489

2-21 2.05 3.18 8.38 1.11 1.41 0.87 359 32

3-24 0.44 2.28 3.03 1.06 0.37 0.60 548

3-22 0.90 2.33 5.69 1.15 0.74 0.65 474

tested at 76 K

2-16 2.18 3.28 15.7 1.45 1.85 0.66 363 43

2-20 1.49 3.36 5.23 0.95 0.94 0.88 512

2-27 0.87 3.15 4.79 1.04 0.68 0.68 545

3-25 1.31 2.33 4.77 1.01 0.85 0.90 436

3-26 0.69 2.28 8.56 1.24 0.65 0.46 527

3-17 0.85 2.31 9.15 1.28 0.78 0.49 418

2-18 1.51 3.21 10.7 1.26 1.28 0.63 459 40

tested at 4 K

1-15 1.62 3.21 10.2 1.24 1.33 0.67 482 42

1-23 0.97 3.28 12.2 1.24 0.91 0.45 596 41

3-36 1.77 2.18 12.9 1.60 1.51 0.70 360 47

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Table 8. Summary of tensile properties of flat

tensiles taken from X2095 SCT specimens.

Temperature YS, MPa UTS, MPa El. , %

from center

295 K 589 618 4

76 K 718 773 4.5

4 K 749 828 5.5

from surface

76 K 566 631 7.5

Table 9. Summary of tensile properties of flat

tensiles taken from 2090-1/2 SCT specimens

Temperature YS, MPa UTS , MPa El., %

machined from

center

295 K 531 552 0.7

76 K 607 621 0.5

4 K 649 690 1.5

machined from

surface

76 K 538 538 0.2

Table 10. Summary of tensile properties of flat

tensiles taken from 2090-3/4 SCT specimens

Temperature YS, MPa UTS, MPa El., %

machined from

surface

295 K 507 533 1.7

76 K 555 589 1.4

15
Large shear lips are evident on fracture surfaces of specimens from

alloy X2095 tested at 295 K when observed in the SEM, indicating that there

was a large plane o component to the stress state at that temperature. In

general, the size of the shear lips decreases as the test temperature decreases. At cryogenic temperatures, the fracture appearance of X2095 specimens

depended on the flaw shape. Flaws with a lower a/c ratio show larger shear

lips .

The influence of a/c ratio on the size of the shear lips is illustrated

in Fig. 6 by comparing the appearance of specimens 2-1 and 2-11, both X2095

specimens tested at 76 K and with nearly the same value of a/$2 /t. For the

deeper and narrower crack (specimen 2-1), the first increment of crack growth

along the surface of the specimen from the fatigue crack has smaller shear

lips. The shear lip remains a constant width of 0.1 mm for approximately 2 mm

along the surface before the width of the shear lips increased to about 0.4

mm. These observations can be taken as proof that there was 2 mm of stable

crack growth along the free surface before final fracture. For the shallower,

wider crack (#2-11), larger shear lips form adjacent to the fatigue precrack.

These observations indicate that there was no slow, stable crack growth prior

to final fracture in specimen 2-11.

For the 2090-3/4 plate, a representative specimen tested at 76 K is

shown in Fig. 7. The fracture surface exhibits small delaminations with

little out-of-plane cracking, 0.5 to 1 mm. Specimens tested at 295 K show

the same small delaminations with occasional out-of -plane cracking, on the

order of 1 to 2 mm.

Specimens from the 2090-1/2 plate usually have more out-of -plane

cracking and delaminations than the thicker plate, 2090-3/4. Figure 8 shows

the fracture surface from one specimen of the 2090-1/2 plate tested 76 K. The

delaminations in the specimen are approximately equal to the grain size, which

are mostly large and not recrystallized. In the 2090-3/4 plate, the grains

were smaller and recrystallized. The grain structure of each material was

shown in the previous report [2].

Discussion

An important consideration in choosing the material for cryogenic fuel

tanks is the ratio of material properties (yield strength and fracture

toughness) at room temperature (295 K) where the tank is proof tested and the

operating temperature [4]

.

The ideal material would show an increase in

toughness commensurate with the increase in yield strength that accompanies

the lower service temperature, similar to the properties of alloy 2219 found

in Table 3. The yield strength and toughness ratios for the three plates of

Al-Li alloys tested in this program are shown in Table 11. The toughness

ratio for the 2090 plates are significantly higher than the ratio for alloy

X2095. The reason for this is the relatively low toughness of the 2090 plates

at 295 K, rather than high toughness of alloy 2090 at cryogenic temperature.

This point is emphasized by looking at the residual strength as a function of

normalized flaw size for all three plates at liquid nitrogen temperature

16
Fig.

6.

(a)

SEM

fractograph

of

the

fracture

surface

of

alloy

X2095,

specimen

#2-1

that

was

tested

at

76

K,

showing

the

starter

notch

(drill

holes)

,

fatigue

precrack

(dark,

hemispherical

area),

region

of

slow

crack

growth

(marked

along

bottom

edge),

and

the

change

in

shear

lip

size

from

stable

(labeled

A)

to

unstable

(labeled

B)

crack

growth
18 Fig.

6.

(b)

SEM

fracograph

of

the

fracture

surface

of

alloy

X2095,

specimen

#2-11

that

was

tested

at

76

K,

showing

the

fatigue

precrack

and

a

relatively

uniform

shear

lip

(labeled

B)

due

to

unstable

crack

growth.
19 Fig.

7.

SEM

fractograph

of

the

fracture

surface

of

alloy

2090-3/4,

tested

at

76

K,

showing

part

of

the

fatigue

precrack

and

the

initial

crack

growth.
20 Fig.

8.

SEM

fractograph

of

the

fracture

surface

of

alloy

2090-1/2,

tested

at

76

K,

showing

part

of

the

fatigue

precrack

and

the

initial

crack

growth.
Table 11. Summary of mechanical property ratios

calculated for Al-Li alloys.

alloy plate

YS ( 76 K) YS (4 K) KT „(76 K) Kt „(4 K)

YS ( 295 K) YS (295 K) KIe (295 K) KIe (295 K)

2090-1/2 1.14 1.22 0.95 1.14

2090-3/4 1.09 — 1.36 1.36

X2095 1.22 1.27 0.92 1.01

shown in Fig. 9. There is little difference between the three except for the

smallest normalized flaws where the residual strength of X2095 depends

critically upon the flaw shape, as discussed in the results section.

There are three possible fracture modes for an SCT specimen. First, the

specimen can fail under plane strain conditions, like the compact tension

specimens tested previously. Plane strain conditions represent the theoretical minimum residual strength for a given flaw size, and the toughness should

be equal to KIc (J) . The second possible fracture mode is plane stress. In

this stress state, the toughness and residual strength are always higher than

in plane strain and depends upon the specimen thickness and yield strength.

The maximum residual strength in plane stress conditions would be for the case

where the material fails by general yielding of the section. Cheng et al. [5]

describe a procedure for predicting the maximum stress cr max where the net

section yields and their equation is shown below

* aeq {l-[(a-2c)/(t.W)]}, ( 1 )

where cr eq is the average of the yield and ultimate strengths measured in the

tensile tests, a and 2c are the dimensions of the surface crack, and t and W

are the thickness and width of the specimen's gage section. The value of omAX calculated in this way would be equal to the residual strength of the specimen

under general yielding conditions.

The results for alloy X2095 at 76 K can be used as an example of how the

failure mode affects the measured residual strength. Figure 10 shows the

measured data with respect to the maximum and minimum predicted residual

strength. A simulated flaw, which increases with a constant a/c ratio of 0.2,

is used to calculate the residual strength for the two extremes of plane

strain and general yielding. Most of our data fall between the two extremes,

but closer to the plane strain value. The exception is for the shallow, wide

flaw discussed previously where the residual strength is actually slightly

higher than theory predicts. At the smallest flaw sizes, the theoretical

plane strain failure yields higher predicted residual strength than found for

general yielding, indicating that the tensile properties of the material will

limit the residual strength of a material as the flaw size is decreased.

21
700 CO IT)

^

CO CM

BdlAI ‘HlDN3dlS ivnaisau

o

a>o

CN

03X

O

03 JZ

03>

j= x

u

&£> "O C r-» 0)U U> u cQ

03 lO

<fl o

3 CN

T3 X •rH03 03

03 C

o' 03

O'

b0 22 pc-i

NORMALIZED

FLAW/THICKNESS
700

GO

edi/\i ‘H10N3U1S ivnaisaa

CO

CO

UJ

z

o

23 Fig.

10.

Residual

strength

vs.

normalized

flaw

size

per

unit

thickness

for

alloy

X2095

at

76

along

with

the

predicted

failure

loads

for

two

possible

failure

criteria,

general

yielding

and

plane

strain.
The data generated in this test program can be compared to previously

reported data [4,6]. The data for alloy X2095 tested at 76 K are shown in

Fig. 11. The two tests from [4] are at a relatively small flaw size, and

compare favorably to the one test from this program where the specimen failed

by general yielding. For alloy 2090, the two tests in [6] and a single test

in [4] are shown in Fig. 12 along with our data. Again, there appears to be

some agreement between tests from the different sources.

The two Al-Li alloys tested in this program behave in quite different

ways in the SCT test. Alloy X2095 behaves like an isotropic material with no

appreciable delaminations. Changes in fracture mode from plane stress to

plane strain are possible and need to be considered in the design and testing

of the alloy. The ratio of toughness at cryogenic temperatures to room

temperature is not greater than 1 so that the high tensile strength may not be

useable in design and proof test.

Alloy 2090 fails by the linking up of intergranular delaminations, and

its properties depend critically upon the orientation with respect to the

rolling direction. In the T-S orientation used in this program, the delaminations deflect the fatigue crack, lowering the local stress concentration.

The two plates of 2090 tested in this program are significantly different in

grain structure and size of the delaminations, yet the residual strength and

toughness values for the two were remarkably similar. In either case, the

delaminations seem to produce plane stress fracture over a wide range of flaw

and specimen dimensions. Even the fatigue crack grows along delaminated grain

boundaries, so the flat fracture surface is not observed in this alloy.

Differences between the two plates of 2090 in tensile properties and grain

structure are not reflected in residual strength.

A difference in strength between the surface and mid- thickness of the

plates is observed in both Al-Li alloys. This difference could be due to a change in the cryostallographic texture from surface to mid- thickness . A

similar effect was found previously [2] where the tensile properties at the

mid- thickness for round specimen oriented at 45° to the rolling direction were

less than the longitudinal or transverse tensile properties.

Overall, the results of the SCT testing have shown that the two Al-Li

alloys fail by different mechanisms, but have similar strength and toughness

properties. Alloy 2090 generally has a better toughness ratio than alloy

X2095, but not as consistent as previously found in alloy 2219. The results

also show that the tensile properties can vary significantly, depending upon

the location through the thickness of the plate. Clearly, flat tensiles taken

from the gage section of the SCT specimens are needed to correlate tensile

properties to fracture properties.

The results have not provided a clear understanding of the relationship

between tensile properties and fracture properties. Future testing should

include alloy 2219 for comparison, so that the influence of tensile properties, delaminations, and alloy composition can be evaluated better. A

quantitative evaluation of texture that relates directly to the tensile

properties would help to sort out variations in the materials and could aid in

the inspection of as-received plates.

24
700

oo

o o o o o o

cd in co o>j t-

(/>

(/

)

UJ

*

O

Q

Lii N

BdiAi

j hion3uis ivnaisau

25

Fig.

11.

Same

as

Fig.

10

but

with

data

from

[A]

added.
700

edl/\l ‘H10N3U1S “IVnaiS3H

vO

•U

<0 O

O'o

CN

(V

• S-i w jc > u

jz e w o

&o >-i c <«

<u

1-1 ctf 4-1 4J W Cfl "0

r-H b0 3 C

T3 *H3

w O

0) JS

ctf w

CN

b0

i-t 26 tu

NORMALIZED

FLAW/THICKNESS
Conclus ions

1. The residual strength of SCT specimens of both alloys

decreases as the flaw size increases. The ratio of cryogenic toughness to room temperature toughness for alloy

2090 is generally higher than that found for alloy X2095.

The ratio of yield strengths (cryogenic to room temperature) is higher for alloy X2095 than for alloy 2090.

2. The residual strength for alloy X2095 at cryogenic temperatures depends critically upon the stress state for the

initial crack growth. If the crack grows under plane

strain rather than plane stress, the residual strength

will be lower. Flaw shape determines the state of stress

for the initial crack growth.

3. The residual strength of alloy 2090 did not vary significantly for the two plates tested in this program. The low

tensile ductility of these materials did not translate

into poor residual strength.

4. Both alloys have significantly lower tensile strengths

near the surface of the plate than in the center of the

plate

27
Section 2 ELASTIC PROPERTIES

Elas tic - cons tant Measurement Methods

We used a megahertz - frequency pulse-echo-superposition method to determine the

elastic stiffnesses C using the general relationship

Here, p denotes mass density and v denotes sound velocity.

For mass density, we used Archimedes's method with distilled water as a standard. We estimate the inaccuracy as 0.05%. Sound velocity was measured

by a megahertz -frequency pulse-echo- superposition method. Quartz transducers

were bonded to the specimens with phenyl salicylate for room- temperature

measurements and with a Celvacene- light for lower temperatures. Failure of

these bonds at very low temperatures required using a dimethyl polysiloxane

(silicone fluid with viscosity - 2 x 10* Pa-s at 25°C) or ethanol for bonding.

The specimen holder was placed in a dynamic gas-exchange cryostat, and

temperature was varied using liquid helium. Temperatures were monitored with

a temperature controller using two gold- iron/chromel 0.07% thermocouples, one

in the specimen holder and another in the gas chamber.

Measurements were performed on seven different specimens shown in Table 1.

The chemical composition of each specimen was included in Table 2. For each

of the seven specimens, we measured nine sound velocities corresponding to the

longitudinal elastic constants C n , C22 » C33 and the transverse elastic constants

^««(^3232 and C2323 ) i C 55 (C 1313 and C3131 ) , C66 (C 1212 and C2121 )

. For sound velocities,

we estimate a 0.2% inaccuracy. Thus we estimate less than 0.5% error in

elastic constants.

The study's principal results are reported in Table 12. The table shows mass

densities, elastic constants, and Poisson ratios at ambient temperature. We

calculated longitudinal modulus C 1 and shear modulus G from the arithmetic

average of the longitudinal and transverse elastic constants. All other

elastic constants that describe polycrystalline aggregates relate simply to

these two moduli:

C - pv2

. ( 2 )

Results

Young modulus a E = G(3C2 - 4 G)

CL - G

( 3 )

28
Section 2 ELASTIC PROPERTIES

Elas tic - cons tant Measurement Methods

We used a megahertz - frequency pulse-echo-superposition method to determine the

elastic stiffnesses C using the general relationship

Here, p denotes mass density and v denotes sound velocity.

For mass density, we used Archimedes's method with distilled water as a standard. We estimate the inaccuracy as 0 . 05 %. Sound velocity was measured

by a megahertz -frequency pulse-echo-superposition method. Quartz transducers

were bonded to the specimens with phenyl salicylate for room- temperature

measurements and with a Celvacene- light for lower temperatures. Failure of

these bonds at very low temperatures required using a dimethyl polysiloxane

(silicone fluid with viscosity - 2 x 10 4 Pa-s at 25 °C) or ethanol for bonding.

The specimen holder was placed in a dynamic gas-exchange cryostat, and

temperature was varied using liquid helium. Temperatures were monitored with

a temperature controller using two gold- iron/chromel 0 . 07 % thermocouples, one

in the specimen holder and another in the gas chamber.

Measurements were performed on seven different specimens shown in Table 1 . The chemical composition of each specimen was included in Table 2 . For each

of the seven specimens, we measured nine sound velocities corresponding to the

longitudinal elastic constants C n , C22> C33 and the transverse elastic constants

^44(^3232 and C2323) » ^55(^1313 and C3131 ) » ^66^1212 ^2121) • For sound velocities,

we estimate a 0 . 2 % inaccuracy. Thus we estimate less than 0 . 5 % error in

elastic constants.

The study's principal results are reported in Table 12 . The table shows mass

densities, elastic constants, and Poisson ratios at ambient temperature. We

calculated longitudinal modulus C x and shear modulus G from the arithmetic

average of the longitudinal and transverse elastic constants. All other

elastic constants that describe polycrystalline aggregates relate simply to

these two moduli:

C - pv2

. ( 2 )

Results

Young modulus = E = G(3C2 - 4 G)

C2 — G

( 3 )

28
Bulk modulus = B = C, — —G . 1 3

( 4 )

n . _

. (Cj - 20 Poisson ratio = v = —-i

2 ( Cj — G)

The elastic constants obtained from these relationships are shown as functions

of temperature in Fig. 13 for the specimen taken from the center of 2090-3/4.

This trend is representative of all the specimens. The elastic constants at

selected temperatures are given in Appendix A. The temperature dependences

were fitted to a theoretical relationship [7]:

C(T) = C( 0)

( 6 )

Here, C(T) denotes elastic stiffness in GPa; C(0) and s with units of GPa and

t with units of K are parameters that can be related to simple atomic models.

Appendix A also gives those parameters determined from a least squares fit.

Discussion and Summary

As shown in Table 12, the mass density shows remarkable variation:

approximately 4% change per mass % Li. It is not surprising because lithium

is the lightest metallic element. Table 12 shows also that texture in these

alloys appears to be not too significant with respect to elastic constants.

In pure aluminum, texture can cause directional elastic -stiffness variation of

up to 20%. Table 12 shows a maximum variation of 4.5%.

Lithium's alloying effect on the elastic constants can not be accurately

determined from this study because of the large number of other elements and

their interactions. However, our results show that shear and Young moduli

increase with lithium content (increase 3 to 4% per mass % Li), while the bulk

modulus and Poisson's ratio decrease (decrease 3% per mass % Li).

All of the elastic moduli increase with decreasing temperature, achieve

zero slope near T - 0, and approach linear behavior at high temperature. The

Poisson ratio also behaves regularly, having a positive temperature coefficient. Between 295 and 4 K, elastic constants without a thermal -expans ion

correction change approximately 10 to 12% in E and G, and 4 to 5% in B and v.

30
TEMPERRTURE (K)

Fig. 13. Elastic properties (normalized to the room temperature

value) vs. temperature for alloy 2090-3/4 with the specimen

taken from the center of the plate thickness. The variation

in properties with temperature is typical of all specimens

tested in this program.

31
Section 3 THERMAL EXPANSION

Materials and Measurement Method

Thermal expansivity of seven different samples of the alloys was measured.

The materials were the same as described in the elastic properties section (see

Table 1) . The change in length of each specimen between 4 and 320 K was measured

with a quartz concentric tube dilatometer. Sample length was determined with a linear variable displacment transducer (LVDT) at 1 K intervals while temperature

was monitored with a Type-E thermocouple placed inside the specimen. The entire

apparatus was calibrated with standard OFHC copper. The coefficient of thermal

expansion CTE (a) is normalized to the room temperature length L0

:

a - (l/L0 )-(dL/dT), (7)

where dL is the change in length for a given change in temperature dT in units

of K.

Results

Figures 14 through 20 show data at 5° intervals plotted as (L-L0 )/L0 , where

Lo is the sample length at 293 K. These points are fit to the function [8]

(L-L0 )/Lq - a + b . (8)

(exp (c/T) - 1)

Here a, b, and c are adjustable parameters relating to the alloys' physical

properties and Einstein temperature. T is the sample temperature in Kelvin. The

derivative of this function provides a smooth curve for the coefficient of

thermal expansion. Both results are drawn with the raw data in Figs. 14-20, and

tabulated results of the curve fits are shown at 10K intervals in Appendix B.

Figures 21 and 22 show the results grouped by base material, and Fig. 21 compares

our data for alloy 2219-T87 with Rhodes, et al. [9] data for 2219-T81 from 1963.

Discussion and Summary

A nth degree polynomial is often chosen for the fit of (L-L0 )/L0. However,

this function has no physical basis and exhibits large errors near the endpoints

of the data set. The present function is chosen because of its relation to

elastic properties, and is suitable for materials that show ordinary temperature

dependence -- that is, zero slope at low temperature and a smooth monotonic

increase to linear behavior at high temperature, with no phase transitions.

Analysis of the fit of thermal expansion data for high purity copper and

aluminum to this function for calculating CTE shows that the difference between

the measured data points and the curve is less than 5%. This is sufficient to

account for the difference between samples of alloys 2090 and X2095 (Figs. 21 and

22 ).

32
TEMPERATURE, K

Fig. 14. *L/L0 and CTE vs. temperature for alloy X2095 Clot 1)

33
(L<T)-L„)/L

0

x

10

5

«

(L(T)

-L

0

)/L

200 23

1 00

0

o - 1 aa

r—

X

-200

-300

-4BB

-300

-EBB

0 50 300 150 200 250 300 350 400

TEMPERATURE, K

16. *L/L0 and CTE vs. temperature for alloy X2095 (lot 3).

x2095 Lot 3

TEMPERATURE, K

Fig. 17. a L/Lq and CTE vs. temperature for alloy 2090-T81 -1/2.

34
VCvfDi)

i

,oi x

V(°v(i)i)

18. *L/L0 and CTE vs. temperature for alloy 2090-T81 -3/4 taken from the

center of the plate.

Fig. 19. *L/L0 and CTE vs. temperature for alloy 2090 -T81 -3/4 taken from the

near- surface area of the plate.

35

CTE
TEMPERATURE, K

Fig. 20. *L/L0 and CTE vs. temperature for alloy 2219-T87.

36

CTE
(L(T)-L

<)

)/L

<) x

10’

»

(

L

(T)

-

0

)/L

TEMPERATURE, K

21. *L/L0 and CTE vs. temperature for the three lots of alloy X2095.

TEMPERATURE, K

Fig. 22. a L/L0 and CTE vs. temperature for the three different specimens of

alloy 2090.

37

CTE

x

10b

,

K.'1

CTE
The difference between the raw data for alloy 2219 -T87 and Rhodes' data [9]

for 2219-T81 is relatively small, yet the difference in CTE for the two sets of

data is significant (see Fig. 23). The main reason for the deviation in CTE

between today's material and that of three decades earlier is the data analysis

procedure used. We choose this procedure because it is based on a theory with

a physical basis rather than a strictly empirical approach.

38
Fig. 23. *L/L0 and CTE vs. temperature for alloy 2219-T87 (1991) and for 2219-

T851 (1963).

o—Im

x

•—* oo

7^

39
Section 4 THERMAL CONDUCTIVITY

Apparatus

The apparatus used here to measure thermal conductivity is a previously

described unguarded "fixed-point" apparatus [10], based on a method of axial

one-dimensional heat flow. Some modifications have been made since the original

publication appeared. The specimen chamber is shown schematically in Fig. 24.

A specimen of known length and cross-sectional area is compressed between two

isothermal copper blocks at controlled temperatures. Three stainless-steel bolts

clamp the specimen between the two copper blocks; the flow of heat bypassing the

specimen through the bolts is known and well characterized from previous

calibration runs.

Figure 24. Specimen chamber for fixed-point* compression probe.

40
The upper, cooled, isothermal block is anchored to the top of the specimen

chamber, which is usually immersed in one of four constant-temperature

(fixed-point) baths. This upper block determines the cold-side temperature of

the specimen. The nominal temperatures of these fixed-point baths are: 4 K

(liquid helium), 76 K (liquid nitrogen), 194 K (a mixture of dry ice and

alcohol), or 273 K (a mixture of pure ice and water).

The temperature of the lower, heated block is fixed by controlling the

electric power supplied to its attached heater. This determines the hot-side

temperature of the specimen, and establishes a fixed temperature difference

across the specimen. Total power supplied to the hot block is determined from

measurements of the voltage and current to its resistive heating element. Heat

flowing through the specimen is computed by subtracting the calibrated heat flow

through the compression bolts from the total power. For this Al-Li specimen, 88%

to 94% of the total power flowed through the specimens.

AuFe-NiCr thermocouples are used to determine the cold-block temperature and

the difference in temperature between the hot and cold blocks. The temperature

differences established across the hot and cold blocks can be as much as 64 K.

These temperature differences permit the use of different mean temperatures

within the specimen subject to the constraint of the fixed cold-side temperatures. For this set of measurements, the maximum temperature difference

maintained across the specimen was 47 K.

Experimental Procedure

Steady-state measurements were made with the specimen in a vacuum

environment of 8 x 10’ 3 Pa (6 x 10~ 5 Torr) and with the specimen chamber in one

of the fixed-point baths described earlier. The specimen had a 76 nm (0.003 in)

indium foil and thermally conductive grease applied to the two contact surfaces

between the specimen and the apparatus. The grease was used as a lubricant to

prevent the indium foil from "cold welding" to the specimen and apparatus.

The specimen had a rectangular cross section 6.95 mm by 5.1 mm and a length

of 25.4 mm. The specimen was clamped between the copper blocks by tightening the

stainless steel bolts to 1.36 N-m (12 in-lb) of torque, applied at room

temperature. This resulted in a compressive pressure on the specimen of

approximately 121 MPa (17.5 ksi)The change in this load resulting from the

cooling of the specimen to cryogenic temperatures, while not accurately known,

is believed to be relatively small and did not affect the measurements of

conductivity reported here. The use of indium-grease contacts coupled with

enough contact pressure (above 90 MPa) is sufficient to permit the influence of

thermal contact resistance to be neglected. After the specimen was compressed

in the apparatus any additional excess grease and indium was removed.

41
Computation of Thermal Conductivity

Knowledge of the power Qspec through the specimen, specimen geometry (length

i and cross-sectional area A) and temperature difference AT across the specimen

allow the mean thermal conductivity, A, to be calculated using the one-dimensional approximation of Fourier's law,

Qspec “ -A-A-(dT/dx) (9)

recast into the approximate form

A - (Qspec /AT).(i/A). (10)

Here the ratio (AT/i) in Eq. (10) approximates the derivative dT/dx in Eq . (9),

and the conductivity obtained is the value averaged over the range of temperature

defined by the temperature difference AT across the specimen.

When the thermal conductivity depends nonlinearly on temperature, as it does

for these specimens, the larger values of temperature difference used during

these measurements can introduce biases in the values of thermal conductivity

calculated from Eq . (10). This is due to curvature of the conductivity function

over the range of temperature AT. These biases were removed during analysis of

the thermal conductivity data by use of an integral technique [11] which gives

the correct functional dependence for the thermal conductivity.

Results

Thermal Conductivity of Alloy X2095 (4%Cu-l%Li):

The thermal conductivity of the alloy X2095 (4%Cu-l%Li) was measured over

the temperature range 4.6 to 291 K. The experimental data are listed in Table

13. The function chosen to fit the thermal conductivity data is of the form

n

X(T) -l a, [in (T+l) ] 1

. (11)

i-1

The resulting values of the six coefficients found to be sufficient to define the

conductivity of this specimen are listed in Table 14. The thermal conductivity

data for the aluminum-lithium alloy and the relative (percent) deviation of the

data points from the fitted curve (Eqn. 10), are shown in Figs. 25 through 27.

As is conventional, all conductivity data in the figures are plotted as a function of the (arithmetic) mean temperature of the specimen.

Figures 28 and 29 shows a comparison of the thermal conductivity for this

aluminum- lithium alloy to that of other Al-Li alloys previously measured. Also

included in the figures are conductivity measurements on the aluminum alloy 2219

for comparison.

42
Table 13. Experimental conductivity as a function of temperature

for alloy X2095 specimen.

Temperature

Difference,

! K

Average

Temperature,

K

Thermal

Conductivity,

W/(m-K)

Cold

Bath

1 4.662 2.30 j£He

2 5.212 2.60

4 6.355 3.20

8 8.782 4.55

16 14.039 7.47

24 19.585 10.5

32 25.293 13.5

1 76.64 36.2 <?N

2 2 77.29 36.4

4 78.56 36.6

8 81.14 37.3

16 86.36 38.8

24 91.68 40.2

32 97.08 41.7

46.9 107.38 44.4

1 192.79 65.5 C0,-alcohol

2 193.63 65.3

4 195.22 65.0

8 198.45 65.9

16 205.10 68.5

24 211.88 70.4

28 215.40 71.3

1 273.95 82.8 Ice-water

2 274.76 82.7

4 276.37 83.1

8 279.62 83.8

16 286.18 85.0

22.2 291.29 85.8

Table 14. Coefficients of X(T) for alloy X2095 using Eqn. 10.

a

i alloy X2095

1 -13.807958

2 25.800305

3 -17.443032

4 5.7295077

5 - 0.86399059

6 0.049828383

43
Thermal

Conductivity,

W/(m

K)

Fig. 25. Thermal conductivity of alloy X2095 (4% Cu and 1% Li). Experimental

data are represented as discrete points. Both scales are logarithmic,

which clarifies the behavior at low temperatures.

Fig. 26. Relative deviations of the experimental and calculated thermal

conductivity for alloy X2095 (4% Cu and 1% Li)

.

44
Thermal

Conductivity,

W/(m.K)

Fig. 27. Thermal conductivity of alloy X2095 (4% Cu and 1% Li). Experimental

data are presented as discrete points. Both scales are linear, which

clarifies the behavior at high temperatures.

45
Thermal

Conductivity,

W/(m.K)

7

7

7

Temperature, K

Fig. 28. Thermal conductivity of selected Al alloys from 4 to 325 K. Both

scales are logarithmic which clarifies the behavior at low

temperatures

.

46
Thermal

Conductivity,

W/(m.K)

— r_

|

“7

2219

Fig. 29. Thermal conductivity of selected Al alloys from 4 to 325 K. Both

scales are linear which clarifies the behavior at high temperatures.

47
Previous measurements on the Al-Li alloy 2090 had significant variations in

the results [1]

.

These studies involved similar specimens; however they utilized

two different measurement techniques to determine the thermal conductivity. The

conductivity differed by approximately 46% over the temperature range.

Additional measurements of the electrical resistivity on the same specimens

indicated that there were similar differences. Therefore there must be

differences between the two specimens and not measurement techniques.

Conductivity of aluminum alloys are very sensitive to variations in composition

and cold-working of the material.

The conductivity of this aluminum- lithium alloy 2095 is 47% higher at 4.6

K and 77 K, and 43% higher at 300 K than the aluminum lithium alloy 2090 that was

previously measured with this apparatus [1] and 23% at 77 K and 16% at 300 K from

the other Al-Li 2090 data [12]. The conductivity of Al-Li alloy 2095 is 62%

lower at 77 K and 41% lower at 300 K than the aluminum alloy 2219 [13].

Accuracy and reproducibility of measurements for moderate conducting material:

The accuracy of the original apparatus for moderate conducting material was

±10% [10]. After some modifications to the apparatus and automating the system,

further tests on a stainless steel standard reference material (SRM 735) have

indicated an overall system accuracy of ±5% (when measuring specimens having a conductivity similar to that of stainless steel)

.

The accuracy of this apparatus

for highly conductive materials has been studied by measuring the sintered

tungsten SRM (8422)

.

These measurements indicated the overall system accuracy

to be ±8% when measuring highly conductive materials. Based on experience with

this apparatus the imprecision has been found to be near 1% for a given specimen

mounting and no more than ±5% for specimen remounting in the apparatus.

Therefore the uncertainty of the results for this moderately conducting material,

aluminum-lithium, is estimated to be ±6%. The maximum positive and negative

deviations (Fig. 26) of the data from the fitted correlation is about 1.5 and 1.3

percent respectively.

48
OVERALL SUMMARY

The results of SCT testing have shown that the two Al-Li alloys have similar

strength and toughness properties even though they fail by different mechanisms.

Alloy 2090 generally has a better toughness ratio than alloy X2095. The results

also show that the tensile properties can vary significantly, depending upon the

location through the thickness of the plate. Clearly, more work needs to be done

to understand the variation in mechanical properties through the thickness of

plate products.

The physical and thermal properties of several Al-Li alloys have been

measured as a function of temperature between liquid helium and room temperature.

In general, these alloys behaved in a normal fashion and did not display any

anamolous behavior or phase transitions. Li lowers the density, bulk modulus,

and Poisson's ratio of the alloys while raising the shear and Young's modulus.

The CTE vs. temperature curve displays a near zero slope near liquid helium

temperature, increasing to a constant slope near room temperature. The thermal

conductivity of alloy X2095 was lowest at liquid helium temperature, increased

by a factor of 25 at 76 K, and was 37 times larger at room temperature.

ACKNOWLEDGEMENTS

We thank Reynolds and ALCOA for supplying the materials used in this

study. The help of J.D. McColskey and R.L. Santoyo of NIST in setting up the

fixtures for the SCT testing was invaluable.

REFERENCES

1. N.J. Simon, R.P. Reed, and E.S. Drexler, "Review of Mechanical and

Physical Properties of Al-Li Alloys and Alloy 2219," report #AL-TR-90-

064, Astronautics Lab (AFSC) , Edwards AFB, CA and to be published as an

NISTIR, Boulder, CO (1991).

2. R.P. Reed, P.T. Purtscher, N.J. Simon, J.D. McColskey, R.P. Walsh, J.R.

Berger, E.S. Drexler, and R.L. Santoyo, "Aluminum Alloys for ALS

Cryogenic Tanks: Comparative Measurements of Cryogenic Mechanical

Properties of Al-Li Alloys and Alloy 2219," to be published as NISTIR

3979, Boulder, CO (1991).

3. ASTM E 740-88, "Standard Practice for Fracture Testing with SurfaceCrack Tension Specimens," ASTM Book of Standards . American Society for

Testing and Materials, Philadelphia, pp . 676-683 (1990).

4. W.T. Tack and L.W. Loechel, "Use of Applied Fracture Mechanics

Principles to Evaluate the Cryogenic Fracture Toughness of Alloy 2090,"

submitted for publication in Al-Li conference proceedings, Garmisch,

Germany, Oct. 1991.

49
5. Yi-Wen Cheng, R.B. King, D.T. Read, and H.I. McHenry, "Post-Yield Crack

Opening Displacement of Surface Cracks in Steel Weldments," in Fracture

Mechanics: Fifteenth Symposium . ASTM STP 833, R.J. Sanford, ed. , American Society for Testing and Materials, Philadelphia, pp . 666-681

(1984).

6. NLS Huntsville Area Review Meeting, Nov. 19-20, 1991.

7. Y.P. Varshni, "Temperature Dependence of Elastic Constants," Phys . Rev.

B, 2, p . 3952 (1970).

8. H. Ledbetter, "Thermal Expansion and Elastic Constants," Int. J.

Thermophys., 12 (4) . pp . 637-642 (1991).

9. B.L. Rhodes, C.E. Moeller, V. Hopkins, and T . I . Marx, "Thermal Expansion

of Several Technical Metals from -255 to 300°C," in Advances in

Cryogenic Engineering, Vol. 8, ed. K.D. Timmerhaus, Plenum Press, New

York, pp. 278-286 (1963).

10. J.G. Hust and J. Arvidson, "Thermal Conductivity of Glass Fiber/Epoxy

Composite Support Bands for Cryogenic Dewars," Internal Report No.

275.03-78-2, National Bureau of Standards, Boulder, Colorado (1978).

11. J.G. Hust and A.B. Lankford, "Comments on the Measurement of Thermal

Conductivity and Presentation of a Thermal Conductivity Integral

Method," Int. J. Thermophys. 3 (1) . pp. 67-77 (1982).

12. R.E. Taylor, H. Groot, J. Larimore, "Thermal and Specific Heat of

Aluminum- Lithium Alloy 2090," Thermophysical Properties Reesearch

Laboratory, Purdue University, West Lafayette, Indiana, Report No. TPRL

878, 14 pp. (1989).

13. B.L. Rhodes, C.E. Moeller, and H.J. Sauer, "An Apparatus for Determining Thermal Conductivity of Solids from 20 to 600 K," Cryogenics,

5, pp. 17-20 (1965).

50
APPENDIX A: TABLES OF PHYSICAL PROPERTIES

AS A FUNCTION OF TEMPERATURE

51
7 Oct 1991

Material : LiAl-2090

Longitudinal Shear Bulk Young

Temp (K) Modulus (GPa) Modulus (GPa) Modulus (GPa) Modulus (GPa) Poisson Rat

295 112 .

7

30.40 72 . 18 79 . 97 0 . 3153

290 112.9 30.48 72.26 80.18 0.3150

280 113.4 30.65 72.58 80.61 0 . 3 149

270 113 .

7

30.81 72 . 65 80 . 99 0.3142

260 114 .

1

30.98 72.82 81.40 0.3136

250 114.4 31.13 72.91 81.76 0 .3130

240 114.7 31.27 73.06 82.10 0.3126

230 115.1 31.45 73 . 16 82 . 53 0 .3119

220 115.4 31.62 73 . 30 82 . 95 0 . 3114

210 115.7 31.82 73 .36 83.40 0.3105

200 116.0 31.96 73.44 83.73 0 .3099

190 116.4 32 . 14 73 . 62 84 . 17 0 . 3094

180 116.6 32.30 73.59 84 . 54 0.3035

170 117.1 32.49 73 . 77 85.01 0 . 3079

160 117.4 32.64 73.87 85.35 0.3074

150 117.6 32.79 73.91 85.71 0 . 3067

140 117.9 32.93 74.03 86.04 0 . 3062

130 118.3 33 . 09 74.23 86.43 0.3059

120 118.5 33.24 74.26 86.79 0 . 3052

110 118.8 33.37 74 . 37 87 . 10 0 . 3043

100 119.0 33.51 74 .40 87.42 0.3041

90 119.2 33.65 74.41 87.72 0.3035

80 119.4 33.77 74.38 88.01 0.3027

70 119.6 33.89 74.45 88.28 0.3023

60 119.8 33.99 74.49 88 .52 0.3019

50 119.9 34 . 07 74.49 88 .70 0 . 3015

40 119.9 34.14 74.44 88 .85 0 . 3010

30 120.0 34.17 74.51 88.92 0 .3011

20 120.1 34.18 74 . 60 88.96 0 .3012

10 120.2 34.18 74 . 64 88.96 0 . 3013

5 120.2 34.18 74.64 88.96 0.3013

Recommended parameters:

Co: 120.11 34.181 74.544 88.942 0.3011

s: -7.6382 -2.9778 -4.5512 -7.4143 0 . 009

t: 213.406 170.969 332.697 177.879 141.22

Equation:

C (T) = Co + s / (-1 + EXP ( t / T )

)

52
7 Oct 1991

Material : LiAl-2095-Wl

Longitudinal Shear Bulk Young

Temp (K) Modulus (GPa) Modulus (GPa) Modulus (GPa) Modulus (GPa) Poisson Rat

295 113 .

28.78 74 .73 76.52 0.3293

290 113 .

28.86 74 .78 76.73 0.3239

280 113.6 29.04 74.89 77.15 0.3233

270 113.9 29.23 74.98 77.61 0.3274

260 114.2 29.38 75.10 77.99 0.3269

250 114 .

29.53 75.28 78 .34 0.3265

240 114.9 29.70 75.31 78 . 77 0 .3256

230 115.2 29.90 75.35 79.22 0 . 3247

220 115.6 30.06 75.51 79.63 0 .3242

210 115.9 30.22 75.68 80 . 03 0.3237

200 116.3 30.38 75.79 80.41 0.3231

190 116.5 30.55 75.84 80.80 0.3224

180 116.8 30.71 75.90 81.18 0.3217

170 117.3 30.87 76.18 81.59 0.3215

160 117.6 31.03 76.26 81.97 0.3208

150 117.9 31.17 76.38 82.32 0.3203

140 118.3 31.35 76.53 82.75 0 . 3 197

130 118.6 31.49 76.65 83.10 0.3193

120 118.8 31.62 76.67 83.39 0.3187

110 119.1 31.75 76.79 83.72 0.3133

100 119.4 31.91 76.88 84 . 10 0.3176

90 119.7 32.05 76.97 84 .43 0.3171

80 119.9 32.11 77 . 14 84 .61 0 . 3172

70 120.2 32.15 77.33 84.72 0 .3174

60 120.4 32.26 77.44 84.98 0.3171

50 120.5 32.29 77.48 85.07 0.3170

40 120.7 32.30 77.69 85.10 0.3174

30 120.7 32.34 77.66 85.19 0.3171

20 120.7 32.34 77.67 85.19 0.3171

10 120.8 32.34 77.68 85.19 0.3172

5 120.8 32.34 77.68 85.19 0.3172

Recommended parameters:

Co: 120.82 32.339 77.737 85.189 0 . 3171

s: -5.7252 -4.3742 -0.8078 -10.204 0 . 0274

t: 163.728 236.098 69.3536 229.254 34 4.94

Equation:

C (T) = Co + s / (-1 + EXP ( t / T )

)

53
7 Oct 1991

Material :LiAl-2090C

Longitudinal Shear

Temp (K) Modulus (GPa) Modulus (GPa)

295 112 .

6

30.55

290 112 .

8

30.63

280 113 .

4

30.80

270 113 .

6

30.96

260 114 .

0

31.13

250 114 .

3

31.28

240 114.7 31.42

230 115.0 31.60

220 115.4 31.78

210 115.7 31.97

200 116.0 32.11

190 116.4 32.29

180 116.6 32.46

170 117.0 32.65

160 117.3 32.80

150 117.5 32.95

140 117.8 33.09

130 118.3 33.25

120 118.5 33.41

110 118 .

8

33.54

100 119 .

0

33 . 67

90 119 .

2

33.81

80 119.3 33.94

70 119.5 34.05

60 119.7 34 . 16

50 119.8 34.24

40 119.9 34.31

30 120.0 34.33

20 120.1 34.34

10 120.1 34.34

5 120.1 34.34

Recommended parameters:

Co: 120.06 34.347

s: -7.6351 -2.9923

t: 213.406 170.96

Equation:

C (T) = Co + s / (-1 + EXP ( t / T )

)

Bulk Young

Modulus (GPa) Modulus (GPa) Poisson Ra

71.94 80.28 0.3140

72 . 01 80.49 0 . 3 137

72 . 34 80.92 0.3135

72.40 81.30 0.3123

72.57 81.71 0.3123

72 . 66 82 . 07 0 . 3117

72.81 82 .42 0 . 3113

72.91 82 . 84 0 . 3 106

73 . 05 83.27 0 . 3100

73 . 11 83.72 0 .3091

73.19 84.05 0 . 3086

73.37 84.49 0 .3030

73.33 84 .86 0 . 3071

73.51 85.33 0 . 3065

73.61 85.67 0 .3060

73.65 86.03 0 .3053

73.77 86.37 0 . 3048

73.96 86.75 0.3045

73.99 87 . 12 0 . 3037

74 . 11 87 .43 0 . 303 3 74 . 13 87.75 0 . 3027

74 . 14 88 . 05 0.3020

74.11 88.34 0.3013

74 . 18 88 . 61 0 . 3009

74 .22 88.85 0 . 3005

74.22 89.03 0 .3000

74.17 89.18 0 . 2995

74.24 89.25 0 .2996

74.33 89.29 0 .2997

74.37 89.30 0 .2993

74.37 89.30 0 .2993

74.273 89.274 0 .299

-4.5462 -7.4389 0 . 009

334.953 177.965 14 1.1

54

rn
7 Oct 1991

Material : LiAl-2090S

Longitudinal Shear Bulk Young

Temp (K) Modulus (GPa) Modulus (GPa) Modulus (GPa) Modulus (GPa) Poisson Rat

295 112.4 30.62 71.63 80.41 0 .3123

290 112 .

30.71 71.70 80.62 0.3126

280 113.2 30.88 72 . 03 81.05 0.3124

270 113.4 31.04 72 . 09 81.43 0 . 3117

260 113.8 31.21 72 .26 81.84 0.3112

250 114.1 31.36 72.34 82.21 0.3106

240 114.5 31.50 72.49 82.55 0 . 3102

230 114 .

31.68 72 . 59 82 . 98 0 . 3094

220 115.2 31.86 72.73 83.40 0 . 3033

210 115.5 32.05 72.79 83.85 0 . 3080

200 115.8 32.19 72.87 84.18 0.3074

190 116.2 32.37 73.05 84 . 62 0 . 3069

180 116.4 32.54 73.01 84.99 0 . 3059

170 116.8 32.73 73.19 85.46 0 . 3053

160 117.1 32.88 73.29 85.81 0.3043

150 117.3 33.03 73.32 86.17 0 . 3041

140 117.6 33.17 73.44 86.50 0.3036

130 118.0 33.33 73.63 86.89 0.3033

120 118.3 33.49 73 . 67 87.25 0.3025

110 118.6 33.62 73.78 87.57 0.3021

100 118.8 33.76 73.80 87.88 0.3015

90 119.0 33.89 73.81 88.19 0 .3008

80 119.1 34.02 73.78 88.47 0.3001

70 119.3 34.14 73.84 88.75 0 .2996

60 119.5 34.24 73.89 88.98 0 .2992

50 119.6 34.32 73.88 89.17 0 . 2983

40 119.6 34.39 73.83 89.32 0.2933

30 119.8 34.42 73.91 89.38 0 .2984

20 119.9 34.43 73.99 89.43 0.2985

10 119.9 34.43 74.04 89.43 0 .2986

5 119.9 34.43 74.04 89.43 0 . 2936

Recommended parameters:

Co: 119.83 34.432

s: -7.621 -2.9998

t: 213.406 170.969

73.938

-4.5355

336.862

89.411

-7.4477

178.037

0 . 2934

0 . 0092

141.15

Equation:

C (T) = Co + s / (-1 + EXP ( t / T )

)

55
7 Oct 1991

Material : LiAl-22 19

Longitudinal Shear Bulk Young

Temp ( K) Modulus (GPa) Modulus (GPa) Modulus (GPa) Modulus (GPa) Poisson Rat

295 115.0 27.79 77.99 74.53 0.3407

290 115.1 27.86 77.99 74 .70 0 . 3403

280 115.5 28.00 78.17 75.04 0. 3399

270 115.8 28 . 14 78.28 75.40 0.3394

260 116.1 28.28 78.46 75.75 0 .3390

250 116.4 28.42 78.53 76.10 0 .3385

240 116.7 28.54 78.68 76.39 0.3381

230 117.0 28.66 78 . 80 76.68 0 .3378

220 117 .

3

28.80 78.89 77.04 0 .3372

210 117.6 28.95 79.06 77.42 0.3367

200 117.9 29 . 08 79.16 77.72 0.3363

190 118.1 29.22 79.19 78 . 07 0.3356

180 118.4 29.35 79.32 78.38 0.3353

170 118.7 29.51 79.44 78 .79 0.3346

160 119.0 29 . 64 79.53 79.11 0.3342

150 119.3 29.78 79.64 79.46 0.3337

140 119.6 29.91 79.76 79.77 0.3333

130 119.9 30.04 79.85 80.08 0.3328

120 120.1 30.14 79.94 80.34 0 .3325

110 120.4 30.23 80.10 80.57 0.3323

100 120.7 30.36 80.24 80.88 0 . 3320

90 120.8 30.42 80.27 81.03 0.3317

80 121.0 30.46 80.41 81.15 0.3313

70 121.2 30.53 80.51 81.32 0.3316

60 121.3 30.54 80.60 81.36 0.3317

50 121.4 30.60 80.64 81.49 0.3315

40 121.5 30.63 80.71 81.58 0.3315

30 121.6 30.65 80.77 81.63 0.3315

20 121.7 30.65 80.86 81.64 0.3317

10 121.6 30.66 80.76 81.65 0.3314

5 121.6 30.66 80.76 81.65 0.3314

Recommended parameters:

Co: 121.63 30.649

s: -6.6072 -4.0547

t: 205.264 259.191

80.790

-1.5857

133.705

81.619

-9.807

254.911

0.3315

0.0203

338.55

Equation:

C(T) = Co + s / (-1 + EXP ( t / T )

)

56
7 Oct 1991

Material : LiAl-2 09 5-W2

Temp (K)

Longicudinal

Modulus (GPa)

Shear

Modulus (GPa)

Bulk

Modulus (GPa)

Young

Modulus (GPa) Poisson Ratio

295 113 .

28.73 74 . 79 76.41 0 . 3297

290 113 .

28 .81 74 .85 76 , 62 0.3293

280 113.6 28 . 99 74.96 77.04 0 . 3237

270 113.9 29.18 75.05 77.50 0 . 3273

260 114.2 29.33 75.17 77 . 88 0 .3273

250 114.6 29.47 75.35 78.23 0.3269

240 114.9 29.65 75.38 78 . 65 0.3261

230 115.2 29.85 75.42 79.11 0.3251

220 115.6 30.01 75.58 79 . 52 0.3246

210 115.9 30.17 75.75 79 .91 0.3241

200 116.3 30.33 75.86 80 . 29 0 . 323 5

190 116.5 30.49 75.91 80.68 0 .3223

180 116.8 30.65 75.97 81.07 0.3221

170 117.3 30.81 76.26 81.47 0.3219

160 117.6 30.97 76.34 81.85 0 .3212

150 117.9 31.11 76.46 82.20 0.3203

140 118.3 31.29 76.60 82 . 64 0 . 3202

130 118.6 31.44 76.73 82 . 98 0.3197

120 118.8 31.56 76.75 83.28 0.3191

110 119.1 31.69 76.87 83 . 60 0 . 3137

100 119.4 31.85 76.96 83 . 98 0.3131

90 119.7 31.99 77.04 84.31 0.3176

80 119.9 32.06 77.22 84 .49 0 .3176

70 120.2 32.09 77.41 84 . 60 0.3173

60 120.4 32.20 77.52 84 .86 0 .3175

50 120.5 32.24 77.56 84 . 95 0.3174

40 120.7 32.24 77.77 84 . 98 0. 3173

30 120.7 32.28 77.74 85.07 0 .3176

20 120.7 32.28 77.74 85.07 0.3175

10 120.8 32.28 77.75 85.07 0.3176

5 120.8 32.28 77.75 85.07 0.3176

Recommended parameters

Co: 120.82

•• 32.282 77.813 85.069 0.3175

s

-5.7252 -4.3665 -0.8143 -10.194 0.0273

t: 163.728 236.098 69.6916 229.278 344 .959

Equation:

C (T) « Co + s / (-1 + EXP ( t / T )

)

57
7 Oct 1991

Material : LiAl-2095-W3

Longitudinal Shear Bulk Young

Temp (K) Modulus (GPa) Modulus (GPa) Modulus (GPa) Modulus (GPa) Poisson Rati

295 112 .

6

28.26 74.93 75.32 0.3324

290 112.7 28.34 74.99 75.53 0.3321

280 113 .

1

28.52 75.10 75.94 0.3314

270 113.4 28.70 75.19 76.40 0.3306

260 113.7 28.86 75.31 76.77 0.3301

250 114 .

1

28.99 75.49 77.12 0 . 3297

240 114.4 29.17 75.53 77.54 0.3289

230 114.7 29.36 75.57 77.99 0 .3279

220 115.1 29.52 75.73 78.39 0 .3274

210 115.4 29.68 75.90 78 .78 0 . 3270

200 115.8 29.83 76.01 79.16 0 . 3264

190 116.0 30.00 76.06 79.54 0 .3257

180 116.3 30.16 76.13 79.92 0.3250

170 116.8 30.31 76.42 80.32 0.3243

160 117.1 30.47 76.50 80.70 0.3241

150 117.4 30.61 76.62 81.04 0 . 3237

140 117.8 30.78 76.77 81.47 0.3231

130 118.1 30.92 76.89 81.81 0.3226

120 118.3 31.05 76.92 82.10 0 . 3220

110 118.6 31.18 77.04 82.42 0.3216

100 118.9 31.33 77.13 82.80 0.3210

90 119 .

1

31.47 77.22 83 . 13 0 . 3205

80 119.4 31.53 77.39 83 .30 0 .3206

70 119.6 31.57 77.58 83.41 0.3208

60 119.9 31.67 77.69 83 . 66 0 .3205

50 120.0 31.71 77.74 83.75 0 . 3204

40 120.2 31.71 77.94 83.79 0. 3203

30 120.2 31.75 77.91 83.87 0 .3205

20 120.2 31.75 77.92 83.87 0 .3205

10 120.2 31.75 77.93 83.87 0.3206

5 120.2 31.75 77.93 83.87 0.3206

Recommended parameters:

Co: 120.29 31.756 77.988 83.872 0.3205

s: -5.7003 -4.2954 -0.8557 -10.079 0 .0267

t: 163.728 236.098 71.9747 229.439 345.04

Equation:

C (T) = Co + s / (-1 + EXP ( t / T )

)

58
APPENDIX B: TABLES OF THERMAL EXPANSION DATA

AS A FUNCTION OF TEMPERATURE

59
COEFFICIENT OF THERMAL EXPANSION OF A1 2090

L-Lo

Lo

CTE < T

)

T#mp

( K ) 10~3 L-LoLo

CCTE)

1 8"6 _1_ dL

CK) Lo dT

3.00 -419.84 . 00

13.00 -419. 34 . 00

23.00 -419.82 . 07

33.00 -419.31 . 70

43.00 -418.10 2.28

33.00 -414.73 4. 48

63.00 -409.09 6 . 84

73.00 -401 . 13 9.03

85.00 -391 . 08 11.01

93.00 -379.21 12.67

103.00 -363.32 14.08

113.00 -331.13 13.26

125.00 -333. 37 16.24

133.00 -318.70 17.07

143.00 -301.28 17.77

133.00 -283.20 18.36

163.00 -264.38 18.87

173.00 -243.49 19.30

183.00 -223.99 19.68

193.00 -206. 13 20.01

203.00 -186.00 20.29

213.00 -163.38 20.34

223.00 -144.93 20.76

233.00 -124.07 20.96

243.00 -103.02 21. 13

233.00 -81.81 21.28

263.00 -60.46 21.42

273.00 -38.97 21.33

283.00 -17.36 21.66

293.00 4.33 21.76

303.00 26. 16 21.86

313.00 48.06 21.94

a 4 4> be

c/T

• - l

»

2 c/T

be , whtr#

c/T 2

< T < t -1))

4 -419.84 10--5

b » 2.33 10^-3

e • 264.1

60
COEFFICIENT OF THERMAL EXPANSION OF A1 2090-S

T*mp

< K )

1 0~5 L-Lo

LO

cCTE)

1 0~6 l dL

k K ) Lo dT

5.00 -41 7. 26 . 00

15.00 -417. 26 . 00

25.00 -417.23 . 10

33.00 -416.31 .91

43.00 -413.07 2.71

53.00 -411.21 5.03

63.00 -404.95 7.43

73.00 -396.42 9.60

93.00 -383.86 11.46

95.00 -373.60 13.02

103.00 -339.91 14.32

113.00 -343.04 15. 39

125.00 -329. 19 16.28

133.00 -312.33 17.03

145.00 -293. 17 17.63

133.00 -277.23 13.19

163.00 -239.93 18.63

173.00 -240.00 19.02

193.00 -220.91 19.35

195.00 -201.31 19.64

203.00 -191.33 19.99

213.00 -161.34 20. 1

225.00 -141 . 34 20.30

233.00 -120.95 20.47

243.00 -100.40 20.63

253.00 -79. 70 20.76

265.00 -39.99 20.99

273.00 -37.94 20.99

293.00 -16.90 21.09

293.00 4.23 21 . 19

305.00 23.43 21.26

313.00 46.73 21.33

L-Lo 4 be

Lo C/T

• - 1

2 c/T

CTE < T ) be • c/T 2

<T<t -l)>

a * -417.26

b * 2. 23

c » 249.73

10--3

10--3

61
COEFFICIENT OF ThERNAL EXPANSION OF x2095 Lot l

Temp

( K ) 10^5 L-Lo

Lo

< CTE)

1 0-6 _1_ dL

i K) Lo dT

5.00 -428 . 0 1 . 08

15.00 -429.01 . 00

25.00 -427.99 . 06

35.00 -427. 71 . 65

45.00 -426. 37 2. 18

55.00 -423. 12 4. 38

65.00 -417.55 6. 76

75.00 -409.64 9.03

85.00 -399.58 11.04

95.00 -387.65 12.77

105.00 -374. 13 14.24

115.00 -359.25 15.47

125.00 -343.25 16.50

135.00 -326.30 17.37

145.00 -308.55 18.11

155.00 -290. 12 18.74

165.00 -271. i 1 19.27

175.00 -251 . 60 19.73

185.00 -231.66 20. 13

195.00 -211 . 36 20.47

205.00 -190. 73 20.78

215.00 -169.82 21.04

225.00 -148.66 21.28

235.00 -127.28 21 . 48

245.00 -105.70 21 . 67

255.00 -83.95 21 . 33

265.00 -62.04 21 . 98

275.00 -39.99 22. 1 1 285.00 -17.82 22.23

295.00 4.47 22.34

305.00 26.86 22.44

315.00 49.34 22.53

L-Lo * be

Lo c^T

• - 1

2 c/T

CTECT) « be e , where

C/T 2

<T<# -1>>

* -428.01

b * 2.39

c « 268.83

10--5

10--5

62
COEFFICIENT OF THERnflL EXPANSION OF <2093 Lot 2

Temp

< K )

1 0''3 L-Lo

LO

<CTE>

19-6 l dL

CIO L o d T

3.00 -406. 1 1 . 00

15.00 -406. 1 1 . 00

25.00 -406. 10 . 04

33.00 -403.90 . 47

45.00 -404.88 1 . 72

33.00 -402.23 3.63

65.00 -397.30 3.84

73.00 -390.36 8.00

85.00 -381 . 35 9.97

95.00 -370.70 11.70

105.00 -338.25 13,17

113.00 -344.43 14.43

123.00 -329.43 13.49

133.00 -313.30 16.39

145.00 -296.71 17.16

135.00 -279.21 17.82

165.00 -261 . 1 1 13.38

173.00 -242.48 18.86

185.00 -223.41 19.28

195.00 -203.94 19.63

203.00 -184. 13 19.97

213.00 -164.02 20.25

225.00 -143.64 20.50

235.00 -123.03 20.72

245.00 -102.21 20.92

255.00 -81.20 21.09

265.00 -60.03 21.23

275.00 -38.71 21 . 39

283.00 -17.23 21.32

295.00 4.32 21.64

305.00 26.01 21.74

315.00 47.81 21.34

L-Lo * be

Lo exT

t - l

2 exT

CTE < T ) be • , whert

C/T 2

< T < • -1))

4 -406 . 1

b 2.33

c * 282.96

10 —5

10 —5

63
COEFFICIENT OF THERMAL EXPANSION OF *2093 Lot 3

Temp

< K ) 10~5 L-Lo

L O

< CTE ) 10-6 l dL

( K ; Lo dT

3.00 -428. 36 . 00

13.00 -423.86 . 00

25.00 -428. 84 . 08

35.00 -428. 48 . 79

45.00 -426.91 2.49

33.00 -423.29 4.80

65.00 -417.27 7.23

73.00 -408.90 9.48

85.00 -398.41 11.43

93.00 -386. 1 1 13.11

105.00 -372.27 14.31

113.00 -337. 16 15.68

125.00 -340.99 16.65

135.00 -323.92 17.46

145.00 -306. 10 18. 13

133.00 -287.63 13.73

163.00 -268.66 19.23

173.00 -249.22 19.66

183.00 -229.37 20.02

193.00 -209. 19 20.34

203.00 -188.70 20.62

215.00 -167.96 20.86

223.00 -146.99 21.08

233.00 -123.81 21 . 27

243.00 -104.46 21.44

253.00 -82.94 21.39

265.00 -61.28 21 . 72

275.00 -39.30 21 . 85

285.00 -17.60 21.96

295.00 4.41 22.03

305.00 26.51 22. 14

313.00 48.70 22.23

L-Lo 4 be

Lo C/T

t - 1

CTECT) »

2 c/T

be • c/T 2

< T < • -1))

uhtrt

4 * -428.86

b * 2.33

c « 238.63

10--3

10 —3

64
COEFFICIENT OF THEFMRL E'. PENSION OF R1 2219

T*mp

< K )

1 0 ~ 5 L-Lo

LO

' CTE > 10-6 l dL

‘v K ) L 0 d T

3.00 -405 . 37 . 00

13.00 -403.37 . 00

23.00 -403. 34 . 1 4

33.00 -403.01 1 . 09

45.00 -403.02 3.02

33.00 -398.83 5.39

65.00 -392.23 7.72

73.00 -383.48 9. 78

85.00 -372.80 11.32

95.00 -360.34 12.96

105.00 -346.97 14.14

115.00 -332.33 15.11

125.00 -316.80 15.92

133.00 -300.34 16.39

145.00 -283.67 17.14

153.00 -266.28 17.61

165.00 -248. 46 18.01

173.00 -230.27 18.35

183.00 -211.77 18.65

193.00 -193.00 18.90

205.00 -173.98 19.12

215.00 -134.76 19.31

225.00 -135.36 19.48

235.00 -115.80 19.63

245.00 -96. 10 19.77

235.00 -76.27 19.89

263.00 -56.34 19.99

275.00 -36.29 20.09

285.00 -16. 16 20. 17

293.00 4.05 20.25

305.00 24.34 20.32

313.00 44.69 20.39

L-Lo * * be

Lo c/T

t - 1

2 c/T

CTE < T ) be • , whtrt

c/T 2

<T<t -1)>

* * -403.37

b * 2.14

c * 238.64

10--3

10--5

65
COEFFICIENT OF THERMAL EXPANSION OF A1 2090-C

L-Lo

LO

CTE < T

)

Temp

( K ) 10~3 L-Lo

Lo

r C TE ) 10^6 l dL

Lo dT

3.00 -405. 04 . 00

13.00 -405. 04 . 00

25.00 -405.02 . 08

33.00 -404.67 . 79

45.00 -403. 13 2.43

35.00 -399.62 4 . 64

65.00 -393.82 6.94

75.00 -385.81 9.06

85.00 -373.81 10.90

95.00 -364. 10 12.46

105.00 -330.97 13.76

115.00 -336. 66 14.84

125.00 -321 . 33 15.73

133.00 -305.21 16.51

145.00 -288.38 17. 14

153.00 -270.96 17.68

165.00 -233.04 18. 14

175.00 -234.69 18.54

185.00 -215.99 18.88

195.00 -196.96 19. 17

205.00 -177.66 19.43

213.00 -158. 12 19.65

225.00 -138.36 19.85

233.00 -118.42 20.03

245.00 -98.31 20. 18

255.00 -78.06 20.32

265.00 -57.67 20.45

275.00 -37. 17 20.36

285.00 -16.36 20.66

295.00 4. 15 20.75

305.00 24.94 20.84

313.00 45.82 20.91

* A be

c'T

• - 1

2 c/T

be e , where

c/T 2

< T < e -1>)

4 * -403.04

b 3 2.21

c 3 256 . 1

1

10--5

10--5

66
BL-114A U.S. DEPARTMENT OF COMMERCE

(5-90) NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

A0MAN 15.01 BIBLIOGRAPHIC DATA SHEET

1. PU8UCATION OR REPORT NUMBER

NISTIR 3986

2. PERFORMING ORGANIZATION REPORT NUMBEF

B92-0092

3. PUBLICATION DATE

March 1992

4. TITLE AND SUBTITLE Aluminum-Lithium Alloys: Surface-Cracked Tension Fracture Tests and Physical and Thermal Properties at Cryogenic Temperatures

5. AUTHOR(S)

P.T. Purtscher, M. Austin, S. Kim, and D. Rule

6. PERFORMING ORGANIZATION (IF JOINT OR OTHER THAN NIST, SEE INSTRUCTIONS)

U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

BOULDER, COLORADO 80303-3328

7. CONTRACT/GRANT NUMBER

8. TYPE OF REPORT ANO PERIOD COVERED

9. SPONSORING ORGANIZATION NAME ANO COMPLETE ADDRESS (STREET. CITY, STATE, ZIP)

Air Force Systems Command

Astronautics Laboratory

Edwards Air Force Base, CA

10.

SUPPLEMENTARY NOTES

11. ABSTRACT (A 200-WORD OR LESS FACTUAL SUMMARY OF MOST SIGNIFICANT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBLIOGRAPHY OF UTERATURE SURVEY, MENTION IT HERE.)

Surface-cracked tension fracture tests were conducted in the T-S orientation at 295, 76, and 4 K on two plate alloys (X2095-T851, pla

thickness of 12.7 mm and 2090-T8 1 , plate thicknesses of 12.7 and 19.1 mm). The cryogenic toughness to room temperature toughne

ratio for alloy 2090 is generally higher than that found for alloy X2095. Both alloys have significantly lower tensile properties near tl surface of rolled plate than in the center of the plate.

The physical properties of seven plate specimens were measured from liquid helium to room temperature. Three variations in chemic.

composition of alloy X2095, three different samples of alloy 2090, and a single sample of alloy 2219-T87 were included. The mass densi

of A1 alloys decreases by 4 % / mass % of Li. The influence of texture on elastic properties is considered minimal because there is le than 5 % variation in elastic-stiffness in the Al-Li alloys. The shear and Young’s moduli increase 3 to 4% / mass % Li. The bulk moduli

and Poisson ratio decrease by 3 % / mass % Li.

Thermal expansion between 4 and 320 K was measured on the same seven plate specimens included in the physical properties study. A

of the materials showed a typical temperature dependence where the slope of the coefficient of thermal expansion (CTE) vs. temperatu: curve has a zero slope near absolute zero and a smooth monotonic increase to a constant slope near room temperature.

The thermal conductivity of alloy X2095 (4%Cu-l %Li) was determined over die temperature range 4.2 to 300 K using a steady-sta; apparatus. The conductivity at 290 K was approximately 40% higher than at 77 K and was 37 times that at 4.6 K. The therm

conductivity of alloy X2095 is approximately twice that of alloy 2090, previously measured in the same apparatus. Compared to that < a published literature value for alloy 2219, the thermal conductivity of alloy X2095 is about 65 % lower than for alloy 2219.

12. KEY WORDS (6 TO 12 ENTRIES; ALPHABETICAL ORDER; CAPITALIZE ONLY PROPER NAMES; AND SEPARATE KEY WORDS BY SEMICOLONS)

aluminum-lithium alloys; cryogenic properties; elastic properties; fracture toughness; residual strength; thermal conductivity; therm

expansion

13. AVAILABILITY 14. NUMBER OF PRINTED PAGES

X UNLIMITED 71

FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE TO NATIONAL TECHNICAL INFORMATION SERVICE (NTIS).

• 15. PRICE ORDER FROM SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE,

WASHINGTON, DC 20402. A04

X ORDER FROM NATIONAL TECHNICAL INFORMATION SERVICE (NTIS), SPRINGFIELD, VA 22161. ELECTRONIC FORM
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