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NBSIR 82-2542

niE COPT . £0 NOT leios

mar 1 4 i985

r Micromechanical Properties of Beryllium

and Other Instrument Materials

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Fracture and Deformation Division

National Engineering Laboratory

Automated Production Technology Division

Washington, D.C. 20234

Boulder, CO. 80303

December 1981

Issued August 1982

Prepared for

Office of Naval Research

Department of the Navy

Arlington, VA 22217

Annual Technical Report

1 October 1980-30 September 1981

Contract No. N00014-81-F-0010

Reproduction in whole or part is permitted for any purpose of the United States Government

U.S. DEPARTMENT OF COMMERCE, Malcolm Saldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

NBSIR 82-2542

Micromechanical Properties of Beryilium

and Other Instrument Materials

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Fracture and Deformation Division

National Engineering Laboratory

Automated Production Technology Division

Washington, D.C. 20234

Boulder, CO. 80303

December 1981

Issued August 1982

Prepared for

Office of Navai Research

Department of the Navy

Arlington, VA 22217

Annual Technical Report

1 October 1980-30 September 1981

Contract No. N00014-81-F-0010

Reproduction in whole or part is permitted for any purpose of the United States Government

ANNUAL TECHNICAL REPORT

TO

OFFICE OF NAVAL RESEARCH

MICROMECHANICAL PROPERTIES OF BERYLLIUM

AND OTHER INSTRUMENT MATERIALS

by

Bruce W. Christ and Robert S. Polvani

Fracture and Deformation Division

and

Robert J. Hocken, Bruce Borchardt, and Tom Charlton

Automated Production Technology Division

National Bureau of Standards

Washington, DC 20234

Report to: Office of Naval Research

Materials Division

800 N. Ouincy Street

Arlington, VA 22217

Contract Monitors: Dr. Bruce McDonald

Dr. Gil London

Contract Number: N00014-81-F-0010

NR039-146(9/16/77)

December, 1981

Reproduction in whole or in part is permitted for any purpose by the

United States Government.
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security classification of this page (Whan Data Entarad) REPORT DOCUMENTATION PAGE READ INSTRUCTIONS

BEFORE COMPLETING FORM

1. REPORT NUMBER 2. GOVT ACCESSION NO. N00014-81-F-0010

3. RECIPIENT'S catalog NUMBER

4. TITLE (and Subtllla) Micromechanical Properties of Beryllium and

Other Instrument Materials

5. TYPE OF REPORT 4 PERIOD COVERED

Annual Technical Report to

Office of Naval Res. for FY81

6. PERFORMING ORG. REPORT NUMBER

7. AUTHORfsJ

Bruce W. Christ Robert J. Hocken

Robert S. Polvani Bruce Borchardt

Tom Charlton

8. CONTRACT OR GRANT NUMBERr*;

N00014-81-F-0010

9. PERFORMING ORGANIZATION NAME AND ADDRESS

National Bureau of Standards

Washington, D.C.

10. PROGRAM ELEMENT, PROJECT, TASK

AREA 4 WORK UNIT NUMBERS

Research and Technology Wore

Unit - Summary-NR039-146

n. CONTROLLING OFFICE NAME AND ADDRESS

Office of Naval Research

800 N. Quincy St.

fir! T nn-fiTii^ VA ^??17

12. report date

Decpmber 1981

13. number of pages

1* MONiTo'RrNd agency nSnIE 4 ADDRESSC// di//eren( irom Controlling Oillca) 15. SECURITY CLASS, (oi thIa raport)

15a. declassification/ downgrading SCHEDULE

16. DISTRIBUTION STATEMENT (oi thia Raport)

Document is available to the U.S. Public Through the National Technical

Information Service, Springfield, Virginia

17.

DISTRIBUTION STATEMENT (oi tha abatract antarad In Block 20, II dliierant Irom Raport)

18.

SUPPLEMENTARY NOTES

19.

KEY WORDS (ContInua on ravaraa aida it nacaaaary and Idantlly by block numbar)

Beryllium, Dimensional Stability, Engineering Design, Gyroscopes, Materials

Science, Microcreep Rate, Micro-deformation

20.

abstract (ContInua on ravaraa aida ii nacaaaary and Idanllty by block numbar)

A program has been underway at the National Bureau of Standards since October

1977 to measure and understand the microcreep of materials used in gyroscopes

so that dimensional instability can be improved. A methodology for microcreep

testing has been developed and is described herein. Tensile microcreep test

results between room temperature and 62®C on 1-400 beryllium indicate that the

microcreep strain does not exceed 10 x 10-6 in three months for applied stressts

up to 20,000 psi. The microcreep rate of 1-400 beryllium does not appear to

1473 edition of 1 NOV 65 IS OBSOLETE

S/N 0102- LF- 014- 6601 nn 1 JAN 73 SECURITY classification OF THIS PAGE (Whan Data Bntaradj
security classification of this page (KTian OMa EntaraO

be Strongly temperature dependent in the range, 45 to 90®C, The phenomenon

of microcreep exhaustion has been demonstrated experimentally and interpreted

in terms of dislocation deformation processes. It is suggested that

suitable micromechanical processing to promote microcreep exhaustion might

serve as a method to improve dimensional stability of 1-400 beryllium. The

possible existence of a correlation between the microcreep stress required

to produce a given strain rate and the 0.2% offset yield stress has been

explored. This report includes descriptions of efforts to develop instrumentation to measure uniaxial strain at 62°C in the range, 10"^ to 10"' and

biaxial strains at room temperature in the range, 10’^ to 10"®.

S/N 0102- LF- 014- 6601

SECURITY CLASSIFICATION OF THIS PACEfP»i»" Dmtm Bntmnd)
Part A

ANNUAL TECHNICAL REPORT

to

OFFICE OF NAVAL RESEARCH

MATERIALS DIVISION

MICROMECHANICAL PROPERTIES OF BERYLLIUM

AND OTHER INSTRUMENT MATERIALS

by

B. W. Christ and R. S. Polvani

Fracture and Deformation Division

Center for Materials Science

National Bureau of Standards

Washington, DC 20234

December 1981
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PART A

ABSTRACT

A program has been underway at the National Bureau of Standards since

October 1977 to measure and understand the microcreep of materials used in

gyroscopes so that dimensional instability can be improved. A methodology for

microcreep testing has been developed and is described herein. Tensile

microcreep test results between room temperature and 62°C on 1-400 beryllium

indicate that the microcreep stain does not exceed 10 x 10’^ in three months

for applied stresses up to 20,000 psi. The microcreep rate of 1-400 beryllium

does not appear to be strongly temperature dependent in the range, 45 to 90°C.

The phenomenon of microcreep exhaustion has been demonstrated experimentally

and interpreted in terms of dislocation deformation processes. It is

suggested that suitable micromechanical processing to promote microcreep

exhaustion might serve as a method to improve dimensional stability of 1-400

beryllium. The possible existence of a corre.lation between the microcreep

stress required to produce a given strain rate and the 0 . 2 % offset yield

stress has been explored.
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MICROMECHANICAL PROPERTIES OF BERYLLIUM AMD

OTHER INSTRUMENT MATERIALS

I. Background of Program

This NBS program was initiated at the National Bureau of Standards on

October 1, 1977. It is sponsored by the Materials Division/Office of Naval

Research and is carried out in cooperation with a related program at the C. S.

Draper Laboratory, Cambridge, MA. These two programs bring together expertise

in metallurgy, materials science and engineering, dimensional metrology and

gyroscope design.

The problem being addressed is the dimensional instability of critical

components of gyroscopes which influence the aim accuracy of missile systems.

Dimensional instability results from microcreep. Such instability is an

irreversible dimensional change which occurs over long periods of time, e.g.,

months, in the absence of applied stress. Residual stresses from machining

are known to influence the dimensional instability of beryllium and other

instrument materials. Fitting up stresses which develop during assembly from

press fits, springing and torquing can also contribute to dimensional

instability.

The objective of these joint programs is to measure and understand the

microcreep of materials used in gyroscopes, so that dimensional instability

can be improved. Drift in gyroscope alignment has been attributed in part to

-6 mass shifts of 10” inches in critical components. Improved dimensional

stability is expected to lessen the need to periodically realign gyroscopes in

service and thereby improve the long term aim accuracy of missile systems.

At the heart of the NBS program are displacement measurements in the

-6 -8

range of 10 to 10 inches. These measurements are made under uniaxial

tensile loading using unique capacitance gauges or laser interferometer

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techniques. Some displacement measurements are made on test specimens which

have sustained biaxial tensile stresses. To date, the focus in the NBS

program has been on beryllium metal. Titanium alloys and stainless steels

have also been used in gyroscopes, but they are less attractive than

beryllium, which has the most favorable combination of mechanical and physical

properties.

Data obtained to date at NBS on the microcreep of beryllium have been

transmitted to the C. S. Draper Laboratory staff for use in the design of prototype gyroscopes. The NBS staff has had interactions with staff at gyroscope

producers such as Honeywell and Northrup.

II. Microcreep Testing Methodology

The tensile microcreep rate is the tensile microstrain per unit time

which occurs at constant stress and temperature under uniaxial tensile

loading. The microcreep stress is usually less than or equal to the microyield stress. The relationship between microcreep and macrocreep is illustrated in Figure 1, where the inset magnifies the microcreep region. The

microcreep region is essentially a very close look at the very early Stage I

portion of the macrocreep curve. The microcreep rate is the instantaneous

slope of the curve showing uniaxial strain vs. time. Because of the

curvature, there is no unique microcreep rate. A microcreep test record which

exhibits an apparent linear steady state behavior can be regarded as a tangent

to the microcreep curve. In a test, strains are measurable and distinguishable from one another when the microcreep strain reaches the minimum detectable

limit of the strain measuring equipment. In the inset shown in Figure 1, this

limit is designated as and is a strain between 10”^ and 10"^.

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Following the tradition for identifing stages in the macrocreep record,

the microcreep record can be conveniently subdivided into Stage i and

Stage ii, as shown in the inset in Figure 1. Stage i is short-lived with

-9 -12

relatively high microcreep rates (10 to 10 /sec), whereas Stage ii is

-12

longer-lived with relatively low microcreep rates (<10 /sec).

Microcreep testing under uniaxial loading requires extreme care in

establishing and maintaining test conditions. For example, temperature

control to plus or minus one one-hundredth of a degree is essential for

-6 -7

reliable strain measurements in the range, 10" to 10” . If a microcreep test

runs for 3-months, the temperature control must be maintained precisely for

the duration of the test. Precise atmosphere control is also necessary if

capacitance gages are used to measure displacements, since the calibration of

the gage is dependent on the composition of the medium in the gap between the

plates. For example, changes in relative humidity can change calibration

significantly.

Alignment of the test system is another major area for precise control.^

A guideline for good practice in microcreep testing is to maintain the

-4

precision of alignment at 10 radians. Repeated unloading to zero stress, as

is sometimes done in microcreep testing to facilitate length-change measurements, can often have an unfavorable influence on alignment. The straightness

of the test specimen itself influences alignment, and precise machining

practice is required to produce straight and/or concentric specimens. If an

extensometer or strain gauges are fastened to the test specimen, the technique

for fastening the extensometer is critical to good alignment.

Test specimen surface condition is another critical factor in producing

reliable microcreep data. Good machining practice can minimize residual

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stresses from surface damage layers. Furthermore, suitable heat treating

and/or etching can remove surface damage layers and residual stresses.

If a data set is to be generated on several test specimens to establish trends

such as the stress and temperature dependence of microcreep rate, good

practice requires that all specimens come from the same region of a single

piece of stock to ensure similarity of microstructure and chemistry. Good

practice also requires that all specimens have the same thermomechanical

history.

Microcreep testing is, by its very nature, an extremely slow process.

The rate at which data are generated can be as slow as four microcreep curves

per year, assuming a 3-month test in a system which operates 100% of the time

and tests one specimen at a time. The rate at which data are generated can be

increased if the number of testing systems is increased and/or if the test

interval is decreased. Short term tests can sometimes be useful for screening

purposes.

If incremental loads are applied to reach the desired microcreep stress,

it is possible to monitor strain during the incremental loading process and

thereby establish the microyield stress of the specimen being tested. This is

useful information for evaluating the metallurgical similarity of several test

specimens in a batch.

Some examples of microcreep test records for 1-400 beryllium taken from

the literature appear in Figure 2 . The records shown in Figure 2a indicate an

approximately parabolic dependence of microcreep strain on time, whereas the

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record shown in Figure 2b indicates a rather rapid rise initially followed by

leveling off. Records of the type appearing in Figures 2a and 2b are

arbitrarily designated as "Type E" records for convenient reference. Type E

records show a systematic microcreep behavior and can be analyzed to determine

microcreep rates at various times and to establish stress and temperature

dependence of microcreep rate.

The record in Figure 2c appears a bit uneven, with the only evident trend

being a zero slope. This type of record is arbitrarily designated "Type U".

Type U records are not quite as useful as Type E records in establishing

microcreep properties. A Type U record may be indicating problems in testing

methodology, or it may simply be indicating that the applied stress is

insufficient to promote a systematic deformation which is within the detection

limits of the testing system. The latter is thought to be the explaination

5 for Figure 2c .

Occasionally, something unexpected shows up in a microcreep data set.

For example. Figure 2a does not show the expected systematic trend of

increasing microcreep strain with increasing applied stress. This result may

be indicating problems in the testing methodology, or it may be indicating

that the test specimens do not have similar micromechanical properties,

perhaps due to dissimilar microstructures

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and/or chemistry. Despite this unexpected result, it is clear that the

microcreep strain of these specimens of 1-400 beryllium at stresses up to 7000

-6

psi for 1500 hours does not exceed 10X10“ in/in.

III. Uniaxial Tensile Microcreep Results on Beryllium Generated at NBS in

FY81

A. Experimental

During FY81, 16 microcreep tests were carried out on 6 specimens of 1-400

beryllium. All specimens came from the same region of a single hot pressed

billet in order to promote similarity in the microstructure and chemical

composition of the material being tested. Machining of all test specimens was

carried out in the beryllium machine shop of the C. S. Draper Laboratory,

Cambridge, MA, according to a procedure for minimizing surface damage. Heat

treatment following rough machining was carried out using the following

schedule to minimize residual stresses. Samples were brought to the annealing

temperature of 1450°F at a rate of 50 Farenheit degrees per hour, held for one

hour, then cooled to room temperature at 50 Farenheit degrees per hr. Finish

machining was completed using cuts of no more than 0.002-inches each.

Specimens were tested in a dead weight tensile loading system which is

described elsewhere.^ Displacements were measured with a paral lei -pi ate

capacitance-type extensometer so designed and fastened to the test specimen

that precision of alignment could be evaluated throughout the test. Two

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testing systems with a long term minimum detectable limit of ±3 x 10"^ inches

are currently in use. Microcreep tests were conducted at stresses between 100

and 30,000 psi and at temperatures between 24 and 90°C. In all tests,

-4

precision of alignment was maintained at <10 radians.

B. Microcreep of 1-400 Beryllium at 63°C

Several microcreep tests were conducted at 63°C. This is because

gyroscopes in the systems of interest operate at about 63°C. Some results

appear in Figure 3a.

Figure 3a illustrates one important aspect of the microcreep behavior of

-6

1-400 beryllium, namely that the microcreep strain does not exceed 10 X 10”

in three months for applied stresses up to 20,000 psi. This generalization is

supported by other data obtained at room temperature on different lots of

3-5

1-400 in three other laboratories.

Figure 3a shows that the microcreep strain increases significantly when

stress increases from 20,000 to 30,000 psi. The fourfold increase in microcreep strain shown in Figure 3a correlates with the applied stress approaching

the macroyield stress of 1-400 beryllium, which is estimated to be about

50,000 psi.

Figure 3b is a microcreep record for Invar. Data in Figures 3a and 3b

were generated on the same testing system at NBS. The overall microcreep

behavior and the similarity in behavior for two different materials, 1-400

beryllium and Invar, provides reassurance that the testing methodology is

satisfactory.

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C. Effect of Temperature on Microcreep of 1-400 Beryllium

Figure 4 shows some preliminary test results on the temperature

dependence of the microcreep of 1-400 beryllium between 45 and 90°C. The

applied stress at all temperatures was 10,000 psi. These results do not show

the systematic increase in microcreep rate with increasing temperature which

is expected if the microcreep deformation mechanism were thermally activated.

The fact that the microyield stress of each specimen tested at 45, 75, and

90°C is about ksi indicates that there were no dissimilarities in

microstructure or chemistry among these specimens which could account for a

variation in microcreep rate. It is tentatively concluded that the microcreep

rate of 1-400 beryllium is not strongly temperature dependent in the range, 45

to 90°C. A firmer conclusion must await further test results at various

temperatures.

The relatively high microyield stress of the specimen tested at 63°C,

22.3 ksi vs. 6.0^Jksi for the other test specimens in Figure 4, may account

for the greater microcreep resistance shown in the 63°C test.

D. Microcreep Exhaustion

An interesting aspect of the microcreep behavior of beryllium is the

phenomenon of microcreep exhaustion, which is a decrease in the capacity for

continued microstrain in a microcreep test. Microstrain exhaustion is

o illustrated in Figure 5, which is taken from Polvani and Christ. Here, a

single specimen of 1-400 beryllium at 62°C was subjected to seven stress

cycles in the range, 1 to 15 ksi. Figure 5a. The microcreep strain was

measured in each cycle and is plotted in Figure 5b. The results show that

once a critical amount of microcreep strain has occurred, i.e., 10 to

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microcreep strains. Rather, the microcreep strain and the microcreep strain

rate diminish significantly as the later, higher stresses approach the microyield stress. This result demonstrates that the micromechanical history of a

test specimen can have a significant influence on its microcreep behavior.

Figure 6 shows another demonstration of microcreep exhaustion. In this

case, a test specimen of 1-400 beryllium was loaded three consecutive times to

an applied stress of 30,000 psi. As the tabulation below shows, the total

microcreep strain at 30,000 psi decreased significantly following the first

loading, and the microyield stress increased significantly.

TOTAL MICROCREEP STRAIN AND MICROYIELD STRESS

IN CONSECUTIVE LOADINGS AT 30,000 psi

Total Microyield

Loading Microcreep Strain Stress (ksi)

First 78 X 10"^ 12.5

Second 22 X 10"® 19.0

Th i rd 18 X 10"® 21.9

Furthermore, results in Figure 6 show that microcreep exhaustion seems to:

1) reduce significantly the strain at which Stage i is complete, and 2) reduce

significantly the limiting microcreep rate in Stage ii.

The test specimen which produced the results in Figure 6 exhibited

remarkable stabilty during a 340 hour test at an applied stress of 100 psi and

a temperature of 24®C after the third loading, as demonstrated in Figure 7.

This Type U microcreep record is a further illustration of the concept of

microcreep exhaustion.

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Microcreep exhaustion is explainable in terms of dislocation

deformation processes. The following equations relate strain and strain

rate to average dislocation density and velocity,

(la)

(lb)

where

Tp = average strain

= average strain rate

b = Burger's vector

- = average mobile dislocation density

- = average dislocation velocity

- = average mean free path for individual glide

^ dislocations

Since the average dislocation velocity is a single-valued function of the

average stress on a dislocation, microcreep exhaustion results from the

reduction in the average mobile dislocation density through source depletion

and/or immobilization of glide dislocations. Only significantly higher

stresses will promote further microcreep strain and maintain microcreep strain

rate through increased dislocation velocity and possibly activation of new

dislocation sources.

Results in this section suggest that suitable micromechanical processing

might serve as a method to promote dimensional stability of 1-400 beryllium.

For example, unaxial tensile microdeformation might serve to stabilize gyroscope components such as rods and screws which support tensile loads in

service. Multi axial microdeformation might be explored as a means to promote

dimensional stability of gyroscope components which support multiaxial

stresses. It seems worthwhile to consider exploring the phenomenon of microcreep exhaustion in other grades of beryllium as well as other materials.

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E. Correlation Between Microcreep Rate, Microyield Stress and Yield Stress

There is some interest in determining whether or not correlations exist

between the microcreep rate, the microyield stress, and the 0.2% offset yield

stress for the different grades of beryllium. Such correlations would be

useful for materials selection and materials procurement because

easy-to-obtain test results, namely, macroyield stresses, could serve as the

basis for estimating results of the more difficult micro-measurements. The

possibility of establishing such correlations on a fundamental basis rests on

whether or not the deformation processes during microcreep, microyielding and

9 macroyielding are the same. Data by Bonfield indicate that they are. It is

expected that they would be the same if: 1) The microstructures are essentially the same from grade to grade, i.e., same dislocation sources and same

barriers to dislocation glide, and 2) the difference in stress amplitude

between micro- and macro-plasticity does not change the deformation process

significantly. It has been pointed out that single crystal test results show

that only basal plane slip occurs at stresses below about 1 ksi^^. Although

this change in slip mode may have some influence on correlations , some

preliminary attempts at correlations have been made, with results shown in

Figures 8 and 9.

The trend line in Figure 8 indicates that the microcreep stress increases

as the microyield stress increases. Specifically, it indicates that a 21,000

psi increase in the applied creep stress is required to produce a microcreep

-13

rate of 1.1x10 /sec. when microyield stress increases from 10,000 to

48,000 psi. Two different grades of beryllium were used to establish this

trend line. The slope is about 0.5. It is conceivable that the slope of the

correlation plot varies with the microcreep rate at which it is determined. A

11
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positive intercept of about 2 ksi on the applied creep stress axis is

indicated by extrapolation in Figure 8, though the meaning is not clear. A

zero intercept seems physically reasonable. Clearly, there is a need to

obtain more data to thoroughly investigate this proposed correlation. If a

correlation is substantiated, one consequence would be that the variability in

microyield stress from one production lot to another. Figure 9, could result

in significant variability in the applied stress required to produce a given

microcreep rate.

Figure 9 is a plot of micro- and macro-yield data from the production

quality control records of a commerical producer. This plot indicates that

the microyield stress increases as the 0.2% offset yield stress increases.

The strain rate at which the yield stress was determined was not reported.

The slope is about 01.5. Extrapolation of the trend .line indicates a zero

intercept, which is physically reasonable. This plot is made from data from

four grades of beryllium. The range of stresses results from 1) the inherent

stress differences from one grade to another, and 2) the inherent scatter in

strength from one billet to another, and 3) possibly a variation in the strain

rate at which the yield stress was determined.

Combining the slopes of the linear trend lines in Figure 8 and 9 and

ignoring the possibility of a non-zero intercept in Figure 8, gives the

following correlation between the microcreep stress required to produce a -13

microcreep strain rate of about 10 /sec and the 0.2% offset yield stress,

a = 0.075 (Y.S.) (2)

It is possible that the coefficient in this correlation equation varies

slightly with the strain rate at which the microcreep stress is determined.

Nevertheless, this correlation can serve as a first approximation to assist

designers in the matter of material selection.

12
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IV. Conclusions

1. A testing methodology has been established at NBS during the last four

years for microcreep testing of materials under constant stress uniaxial

tensile loading. Reliable results have been obtained in the strain

range, 1 to 100 x 10”^, on 1-400 beryllium test specimens. The testing

methodology involves careful control of temperature, humidity, and

alignment. Furthermore, the testing methodology requires careful control

of the geometry, dimensions, surface condition and metallurgical

structure of the test specimens. Lastly, the testing methodology

requires that the parallel plate capacitance extensometers used to

measure displacements be fastened carefully to the test specimens.

2. Generation of microcreep data is a very slow process. Under optimum

conditions, a single-specimen testing system can produce four three-month

test records per year.

3. Microcreep test records of microcreep strain vs. time at constant stress

can be classified in one of two categories:

a) A Type E record shows a rapid initial rise (Stage i) followed by a

gradual asymptotic approach to some limiting microcreep strain rate

(Stage ii). This type of record is useful for quantitative analysis of

microcreep properties.

b) A Type U record shows an uneven, nearly-level trace with the only

evident trend being a zero slope. A Type U record may be indicating

problems in the testing methodology or it may be indicating that the

applied stress is insufficient to promote a systematic deformation which

is within the detection limits of the testing system.

13
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The microcreep strain rate of 1-400 beryllium at 62°C which exhibits a -9 -12

Type E microcreep record is typically 10 to 10 /sec in Stage i and

-12

<10 /sec in Stage ii. About 70 to 80% of the microcreep strain in a

Type E test record occurs in the first 100 hours.

The microcreep strain of 1-400 beryllium at 62°C does not exceed

10 X 10"^ in three months for applied stresses up to 20,000 psi.

Microcreep tests were carried out on 1-400 beryllium at temperatures of

45, 62, 75 and 90°C. From these test results, it is tentatively

concluded that the microcreep rate of 1-400 beryllium is not strongly

temperature dependent in the range, 45 to 90°C. A firmer conclusion must

await further test results at various temperatures.

1-400 beryllium tested in uniaxial tension exhibits microcreep exhaustion

which is a decrease in the capacity for continued microstrain in a microcreep test. The discovery of microcreep exhaustion suggests that

suitable micromechanical processing might serve as a method to promote

dimensional stabilty of 1-400 beryllium. Multi axial microdeformation

might be explored as a means to promote dimensional stability in design

situations where multiaxial stresses must be supported.

An approximate correlation between the microcreep stress required to

produce a given strain rate and the 0.2% offset yield stress has been

established for different grades of beryllium, as follows:

a ^^^=0.075 (Y.S.)

14
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,
Acknowledgments

The following individuals have given valuable assistance to various

facets of this test program: Mr. C. S. Tilghman helped with the experimental

measurements; Dr. J. Filiben and Mr. S. Leigh developed computer codes that

were used to analyze and graph the microcreep records; Dr. C. Reeve developed

a method for extrapolating microcreep curves with a high degree of statistical

reliability; Dr. R. deWit assisted Dr. C. Reeve by carrying out a critical

evaluation of the technique for extrapolating microcreep curves.

15
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REFERENCES

1. B. W. Christ and S. R. Swanson: "Alignment Problems in the Tensile

Test," ASTM Journal of Testing and Evaluation, Vol . 4, No. 6, Nov. 1976,

pp. 405-417.

2. National Materials Advisory Board: "Evaluation Test Methods for

Beryllium," National Academy of Sciences, National Research Council,

Washington, D.C. Report No. MAB - 205 - M (1966).

3. C. W. Marschall, R. E. Maringer and F. J. Cepollina: AIAA Paper No.

72-325, 13th Structures Structural Dynamics and Materials Conf . , San

Antonio, TX. April 10-12, 1972.

4. H. S. Starrett: "An investigation of the Dimensional Stability of

Beryllium and Beryllium Oxide". Southern Research Institute,

Birmingham, AL. (1966) SRI Report to M.I.T., Cambridge, Mass., Pruchase

Order IL-4-196951.

5. J. W. Lyons, Jr.: "Absolute Capacitance Microcreep and Dimensional

Stability Measuring System," NASA Report No. TM-X-2046 (1971).

6. B. W. Christ, R. S. Polvani, and R. J. Hocken: "Micromechanical

Properties of Beryllium and Other Instrument Materials." Annual

Technical Report from NBS, Washington, DC to Office of Naval Research,

Boston, Massachusetts. October, 1978.

7. B. W. Christ: "Effects of Misalignment on the Pre-Macroyield Region of

’ the Uniaxial Stress-Strain Curve," Metallurgical Transactions, Vol. 4,

Aug. 1973, pp. 1961-1965.

8. R. S. Polvani and B. W. Christ: "Microcreep of Instrument Grade

Beryllium," SAMPE Quarterly, Vol. 10, No. 4, July 1979, pp. 37-41.

9. W. Bonfield and .C H. Li: "Dislocation Configuration and the

Microstrain of Polycrystal 1 ine Beryllium," Acta Met., Vol. 11 , 1963,

pp. 585-90.

10. G. J. Turner and J. S. White: "The Temperature Dependence of the

Critical Resolved Shear Stresses for Basal and Prismatic Slip in

Beryllium," Scripta Met 6, 123 (1972).

16
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PART A

APPENDIX I - MICROCREEP-CURVE FITTING TECHNIQUES

MICROMECHANICAL PROPERTIES OF BERYLLIUM

AND OTHER INSTRUMENT MATERIALS

INTRODUCTION

Curve-fitting to microcreep data has been carried out using a computer code

called DATAPLOT, which was developed at the National Bureau of Standards to

combine curve fitting with graphics. DATAPLOT is a free-format, English-like

syntax language for:

1. interactive graphics (continuous or discrete)

2. linear or non-linear fitting

3. general data analysis

4. statistical analysis

5. mathematical analysis

DATAPLOT was developed originally by James J. Filliben of NBS in 1977 in

response to data analysis problems encountered at the National Bureau of

Standards. It is a valuable tool not only for "raw" graphics, but also for

manuscript preparation, modelling, data analysis, data summarization, and

mathematical analysis. DATAPLOT may be run either in batch or interactively

DATAPLOT graphics may appear on many different types of output devices. Due

to its modular design and underlying ANSI FORTRAN (PFORT) code, DATAPLOT is

portable to a wide variety of computers.

CAPABILITIES : Processing and Displaying Data

All I/O is format-free. File names may be used directly in DATAPLOT

READ/WRITE command syntaxes. The many graphical, classical, and exploratory

data analysis capabilities listed below serve as tools for the processing and

editing of data files. Sorting and ranking capabilities exist.

Graphics capabilities include continuous display terminal plots (e.g.,

Tektronix), discrete (narrow-width or wide-carriage) terminal plots (e.g.,TI

700), high-speed printer plots, high-quality secondary output plots (e.g.,

Calcomp); on-line interactive definition and plotting of functions; data

plots; superimposed mixture of function and data plots; multi-trace plots;

linear or log scale plots; plots with or without labels, titles, frames, tic

marks, grid lines, legends, legend boxes, arrows, etc.; automatic hardcopying

of plots; 3-d plots of functions and/or data; multi-colored graphics; all of

above for full data sets or subsets of data.

In addition to the DATAPLOT fitting program called NONLIN has been developed

by C. P. Reeve to fit the specific non-linear microcreep equation. This

program is also helpful in establishing the standard deviation or confidence

interval to times much larger than the actual duration of a test.
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Given the observed microcreep strain values e,, ^ ^t times t, , t«,

...t , the statistical model takes the form, ^ n

e, = f(t.) + y.

where the y. are independent error values from a distribution with mean zero

' 2

and variance E .

Of several empirical equations which were evaluated, the following equation

for microcreep strain seemed to give the best fit most often.

e = f(a) = Sq Ajln(l+t/B)

where

e = microcreep strain (plastic)

a = applied stress

e = a parameter which depends on the test methodology and is to be

° estimated. (Physically, is the instantaneous plastic strain

which occurs when stress is applied to the test specimen).

A,B = empirical constants to be estimated.

/V A The least squares estimates of A, and B are termed e^. A, and B. They

are obtained by linearizing the above equation with a Taylor series expansion

and iteratively solving the linear least squares problems.

The predicted value of microcreep strain at time t. is given by the following

least squares estimate, ^

and i

2

is estimated by

+ Ajln(l+t./B)

Z = (ci-e.V

The extrapolated value of microcreep strain at a time t' beyond the measured

time domain is given by

e' = + Ailn(l+t7B)

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where V is the 3x3 approximate un-normal ized variance-covariance matrix of the

A estimates A and B, and h is the 3x1 vector given by

The superscript t denotes matrix transposition.

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where critical point of the t distribution with n-3 degrees

of freedom at the a level of significance.

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LET FUNCTION F«4M«ltOCa-fr/C

)

LET A-e.O

LET t-e.o

LET C-8M.0

FIT $-F

COPT

TITLE MCNOCREEP OF BERYILIUN AT IS ESI

VLAIEL niCROSTRAIN

XILABEL TINE (HOURS)

X3LA8EL RUN AT 62 K6REES C£NTI(»M)E

CftIO OH CHARACTER SIZE l.t CHARACTERS X BLANK

LINES BLANK SOLID

VLIN % 9 XlIN •

41B

489

ENB

•>

PLOT S US T AM

PLOT PRED US T

•o»

OF Flic

/I-OA7APL07 PAOfiR^AI

INPUT FUNCTION

OUTPUT FUNCTION

> A^BSLOeCl^T/C)

• A«BtLOQ(l^T/C> THE NANC F TO THE FUNCTION

HAS JUST BEEN EQUIUALEHCEO — A*B«LOG(l^T-^J

T»C CONFUTED UALLC OF THE CONSTANT A . aOO MM-»Al

THE COmrTED VALUE OF THE CONSTANT B

TIC COHPUTED UALUE OF THE CONSTANT C . 000—0403

LEAST SQUARES NON-LINEAR FIT SANPLE SIZE N • 98

NOOEL—S- (A4B*L0C( 14T/C )

)

NO REPLICATION CASE ITERATION CONUERGENCE

NUNBER NEASURE

1~ .10—-01 8~ .—00-02 3~ .2S000-02

4— . 12—-02 5~ .62500-03

RESIDUAL X standard X DEUIATION X .10468401 X .53378400 X .51790400 X .51532400 X .51528400 X

PARANETER

ESTINATES

.20—401

.10801401

.11316401

.11494401

.11547401

.20—401

.29536401

.34134401

.35682401

.35972401 FINAL PARANETER ESTINATES

1.15557 3.—73

6S4.689

(APPROX. ST. DEV.)

( .1363 )

( .3539 >

( 143.2 ) RESIDUAL STANDARD DEVIATION

RESIDUAL DECREES OF FREEDON

.5152790546

95

.20—403

.41401403

.57476403

.64071403

.65327403

B'OfiT/iPLoy Results

niCROCREEP OF 1-400 AT 10 KSI AND 63 CENTIGRADE

C

R

E

E

P

S

T

R

A

IN

TINE (HOURS)

SOLID-ACTUAL RESULT DASH-FORECAST

1-SIGMA CONFIDENCE BANDS (66X)

r - EXAMPLE Of extrapolation BeYoHOTNE

mASUREO time DOM/9M.

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un 18 CO

PART A

Micromechanical

Speaker Date

B. W. Christ 2/11/81

R. S. Polvani 2/11/81

B. W. Christ 3/23/81

R. S. Polvani 3/24/81

B. W. Christ 5/30/81

APPENDIX III

Properties of Beryllium and Other Instrument Materials

Presentations and Papers in FY81

Organization and Place Title

ONR-NBS-C.S. Draper Lab semiannual review meeting, C. S.

Draper Lab., Cambridge, MA.

VJhere we have been

and where we are going in our quest

for microcreep data

on gyroscope materials.

Same as above Test Results on T-400

Beryl 1 ium at 62°

C

and at Stresses Between

300 and 30,000 psi.

Westec Conference, Los Angeles, Microdeformation in

California Beryllium

Internatinal Conference on Creep Beryllium Microand Fracture of Engineering deformation Mechanisms

Materials and Structures, LIniv.

of Wales, U.K.

Staff of NBS Fracture and The NBS Program on Deformation Div., Boulder, Co. Microcreep and Dimensional

Stability of Materials

For Use in Gyroscopes.

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LIST OF FIGURES

Figure 1 Schematic constant-load, constant temperature uniaxial creep record,

showing the three major stages of creep. The inset is a schematic

showing microcreep records for two stresses. Very small strains are measureable and distinguishable from one another when the strain

reaches the minimum detectable limit of the strain measuring

equipment, which is designated in the inset.

Figure 2 Some typical microcreep test records on 1-400 beryllium from the

1 iterature.

a) Results from the Battelle/Columbus test

program (Ref. 3).

b) Results from the SRI/MIT test program

(Ref. 4).

c) Results from the NASA test program (Ref. 5).

Figure 3 Some typical microcreep test records from the MBS test program.

a) Results on 1-400 beryllium at 62°C.

b) Results on Invar at 24®C.

Figure 4 Effect of temperature on the microcreep strain of 1-400 beryllium

between 45 and 90°C.

Figure 5 Microcreep exhaustion in 1-400 beryllium tested at 62°C.

a) Applied stress vs. time.

b) Microcreep strain per stress cycle vs. time.

Figure 6 Microcreep exhaustion in 1-400 beryllium in successive tests at

30,000 psi and 63°C.

Figure 7 Microcreep record on 1-400 beryllium (24°C) after microcreep at

30,000psi (63®C) to promote microcreep exhaustion and dimensional

stability.

Figure 8 Trend line suggesting correlation between microcreep stress and

microyield stress of different grades of beryllium.

Figure 9 Trend line suggesting correlation between microyield stress and 0 . 2 %

offset yield stress.

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PLASTIC

STRAIN

Figure 1 Schematic constant-load, constant temperature uniaxial creep record,

showing the three major stages of creep. The inset is a schematic

showing microcreep records for two stresses. Very small strains are measureable and distinguishable from one another when the strain

reaches the minimum detectable limit of the strain measuring

equipment, which is designated e in the inset. m
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Room Temperature

Microyield Stress: 8.7 ksi

9.6 ksi r

1 1

1 500 1000 1500

TIME, h

Figure 2 Some typical microcreep test records on 1-400 beryllium from the

1 iterature.

a) Results from the Battel 1 e/Columbus test

program (Ref. 3).

b) Results from the SRI/MIT test program

(Ref. 4).

c) Results from the NASA test program (Ref. 5).
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Figure 3 Some typical microcreep test records from the NBS test program.

a) Results on 1-400 beryllium at 62®C.

b) Results on Invar at 24®C. (o = measured data point, D and

heavy solid line = fitted microcreep curve. A = microcreep curve extrapolated beyond time domain of test. Thin solid lines represent

the three sigma (99%) confidence limits of the extrapolation.
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Figure

4

Effect

of

temperature

on

the

microcreep

strain

of

1-400

beryllium

between

45

and

90°C.

MICROCREEP

STRAIN

(a)

16

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Stress History 80 1-400

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til

40 IV

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—

VI

n L I I J LL 0 400 800 1200

14

8

4

0

< TIME, h

(b)

Figure 5 Microcreep exhaustion in 1-400 beryllium tested at 62*C.

a) Applied stress vs. time,

b) Microcreep strain per stress cycle vs. time.

APPLIED

STRESS,

ksi
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6

Microcreep

exhaustion

in

1-400

beryllium

in

successive

tests

at

30,000

psi

and

63°C.

3x10-®,

lU

s

Nivuis daauoouoiN Figure

7

Microcreep

record

on

1-400

beryllium

(24°C)

after

microcreep

at

30,000psi

(63°C)

to

promote

microcreep

exhaustion

and

dimensiona

stability.

MICROYIELD

STRESS,

ksi

‘ssaais daaao aanddv

ID

CS

O

CM

in

in

CM

(/)

0)

Ul

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H

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Figure

8

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line

suggesting

correlation

between

microcreep

stress

and

microyield

stress

of

different

grades

of

beryllium.
oi

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YIELD

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\s^ ‘SS3U1S QTaiAOUOliM

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Figure

9

Trend

line

suggesting

correlation

between

niicroyield

stress

and

0.2%

offset

yield

stress.

PART B

ANNUAL TECHNICAL REPORT

TO

OFFICE OF NAVAL RESEARCH

MATERIALS DIVISION

INSTRUMENTATION TO MEASURE MICROMECHANICAL

PROPERTIES OF BERYLLIUM

AND OTHER INSTRUMENT MATERIAL

BY

R. J. HOCKEN, B. BORCHARDT, AND TOM CHARLTON

AUTOMATED PRODUCTION TECHNOLOGY DIVISION

CENTER FOR MATERIALS SCIENCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, DC 20234

DECEMBER 1981
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PART B

INSTRUMENTATION TO MEASURE MICROMECHANICAL

PROPERTIES OF BERYLLIUM AND OTHER INSTRUMENT MATERIALS

by

R. J. Hocken and B. Borchardt

THE 1-D MICROCREEP APPARATUS

Since last year’s report on the status of the 1-D microcreep apparatus,

there has been considerable progress on solving its problems. Ilie

stability of the interferometer mount, a problem mentioned in last year’s

report, was carefully measured and solved by designing a new stable kinematic mount for the interferometer. This mount solidly attaches the interferometer optics to the same mounting plate used for the laser and detectors.

The quarter wave plate was also re-moxinted in an adjustable mount, and an improved quarter wave plate was purchased. The new quarter wave plate was

larger in diameter to allow for a larger sample size.

We identified a problem with undesirable mechanical coupling from the outside

shell of the thermostat to the sample positions. The outer shell rests on a rubber-o-ring, and can easily wander. If it firmly connected to the inside

drum, the samples can be shifted relative to the interferometer. The

solution eliminates the coupling by remachining the thermostat insulator to

give some clearance.

Another small source of noise was in the first stage amplifiers from the

photomultipliers. New, better quality operational amplifiers cured this.

To improve the optics, we installed a spatial filter on the input side,

allowing us to use the whole beam width again. We had been using only half

of the width of the beam. The need to split the beam into two halves had

come from the effect of a beam returning into the laser. In effect, this

makes the laser cavity look like a different length and interferes very

strongly with the wavelength control. The spatial filter keeps the returning

beam from passing through, since it is very sensitive to alignment with the

optics. The filter incorporated a beam expander, so the laser could illuminate

larger samples. The mechanics of the thermostat chamber were modified to

allow larger samples: a size of 0.4375 inches O.D. and 0.250 ID was settled on. Larger samples were necessary to improve the optical quality of the signals

at the detectors. The 0.083 inch holes we tried first had effectively no area

left which was not affected by diffraction effects. With a 0.250 hole, the

central area of interest is undisturbed. This larger size quadrupled the area

of the inside section of the pattern, and tripled the area of the outer ring.

The increase in cross-sectional area changed the load limits of the apparatus

(as measured in PSI); the minimum on the loadable samples is now 67 PSI, and

the maximum is about 4000 PSI.

Because of their ready availability, invar samples were obtained in the proper

diameter. After overcoming some mechanical difficulties with the large sample

size and with obtaining good quality "button" reflectors for the bottoms of

the samples, a stability test was taken. The test showed a large improvement

over previous runs in the noise, to a level of about 2 x 10-8 for short term.
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and 5 x 10-8 for long tern intercomparisons. These numbers are for the

samples which were most nearly parallel; the worst samples are 3 or 4

times as bad. The non-parallelism affects noise by introducing a dependence

on cross travel; the apparatus as designed cannot hold horizontal position

perfectly. Thus, the effective length changes as the interferometer moves

to a thicker or a thinner part of the sample.

For the first time, repeated comparison measurements were taken between

different samples over an extended period of time. This procedure gave the

repeatabilities cited above. This was the original intent of the system's

design, finally realized.

At this low noise level, a small drift was detected in the interferometer

output. This was diagnosed as due to a leak in the pressure vessel, which

allowed helium and air to mix, slowly changing the index of refraction.

This problem was solved by pumping continually and taking data at a pressure

of less than 20 microns of mercury. 100 microns (0.1 mm) i^ the resolution

of the barometer; thus the error is less than 3 parts in 10 at this pressure.

In the course of these investigations, a measurement of the index of refraction

of helium was coincidentally made, giving a number in agreement with the

accepted value. This gave us further confidence in the apparatus.

The most significant test was a long term run on the invar samples. The

results obtained are based on a run of 1500 hours (approximately two cwnths)

during which a vacuum was continually maintained (about 15 millitorr at the

pump) and the temperature was controlled within about 8 mK. The pressure

occasionally was raised to about 200 torr of helium for testing. There was occasional excursions of about 1 C when our building air conditioning failed,

exceeding the capacity of the apparatus thermal system to maintain control;

the data obtained during these times were not included. The return to control

temperature, 20.98 C, was verified by a platimun resistance thermometer.

The stress was constant at 67 PSI in tension for Invar 2, 3, and 4. Invar 1,

steel and Cervit were stressed only by their own weight.

The basic results are shown in the attached figures. Note that the vertical

scale is relative phase; this means that a different constant shift has been

added to the data for each sample to separate them vertically on the graph.

The uncertainty brackets represent the short term noise as recorded on the

chart recorder during each data collection period. These periods were

normally 1 or 2 hours, except overnight and during weekends. The shorter

time bases of 2, 3, and 4 reflect the fact that the alignment of each sample

with the interferometer system was occasionally adjusted and only phase values

which were obtained while the system could be shown to be working were retained.

Proof of functioning was considered to be shown by the proper response to a brief (5 minute) injection of pure helium into the system. Since the index of

refraction is increased temporarily, the optical path length as measured by the

interferometer should increase in a linear manner. If the interferometer is

not properly aligned for a particular sample, the pressure response becomes
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nonlinear or, in the worst case, nonexistent. Thus, we have confidence

that all of the points shown on the graph are real and significant.

The least squares slopes are as follows:

sample 1 5.8 + 0.6 nano strains /day

-sample 2 9.3 + 1.9 II

sample 3 14.1 + 0.9 It

sample 4 13.9 + 1.4 If

The uncertainties are one standard deviation. The data are differenced

point by point from the average of cervit and steel. Figure 2 shows the same data plotted without differencing from the steel and cervit sample.

The least sqiiares slopes are:

sample 1 -2.3 + 0.5 nano strains/day

sample 2 +0.5 + 1.1 If

sample 3 +5.7 + 1.1 If

sample 4 +8.3 + 1.5 If

cervit -7.7 + 0.4 It

steel -8.0 + 0.3 II

We cannot say unambiguously whether the drift of the standard samples is

In the sample or in the instrument. These rates are significantly larger

than previous results on gage block instability. However, these blocks

are not typical gage blocks in that both have recently had a hole drilled

down the center, which could release residual stresses and cause instability.

Hence, the rates we see are not outside the bound of possibility. In

addition to instability due to recent machining, other phenomena include a change in the wringing film between the sample and its platen, laser instability (although this is unlikely), and differential deposition of

surface films on the sample and platen. Subtraction of the slope of the

standards may or may not be the correct approach. It is our judgement,

particularly in view of the fact that the two standards are changing together, that what we see is really instrumental drift from some as yet

unknown cause.
I

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DATA

I^L_ATXn7E

TO

STANDARDS

Figure

1

.

.

'

300

600

900

1200

1500

TIME

CHOURS)

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PART B INSTRUMENTATION TO MEASURE MICROMECHANICAL

PROPERTIES OF BERYLLIUM AND OTHER INSTRUMENT MATERIALS

by

R. J. Hocken and T. Charlton

BIAXIAL TESTING SYSTEM

The highlights of this year’s progress on the study of microcreep in

biaxially stressed beryllium include;

a) completion of load fram hardware with photographic data

acquisition system.

b) extensive testing of entire hardware system with steel

dummy samples.

c) loading of two beryllium samples with collections of over

300 data photographs.

d) further development of the image analysis /data reduction

software with extensive testing and improved modularity.

e) preparation of a review report for reference purposes on

the biaxial testing system for the project files.

HARDWARE

The six load frame/interferometer stations were completed and assembled. A

large effort was invested in developing adequate assembly and alignment techniques for the frame structure and interferometer mount since the uniformity

of the loading process was presumed to be very important. Without a uniform

repeatable process for loading the samples, the stress distribution in the

sample could not be reliably calculated for use in the simulation calculations

of Draper Labs.

Three major improvements were made in the frame design as a result of our experience with the load frame assembly. First, a centering guide was added

to the underside of the sample mount. This addition proved necessary for the

satisfactory positioning of the contact ball at the center of the sample

disk. The second addition was a thin guide ring around the sample. This

guide ring was needed to constrain the travel of the sample during loading

to prevent tilting, and thus poor centering for the circumferential loading

against the steel reference flat. The third modification was the addition

of the access ports in the load frame to allow inspection of the guide ring

after loading. These inspection points were needed to assure that the

sample was completely free from the guide ring after loading was complete,

so there is no possibility of unknown lateral stress on the sample.
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TESTING

To assure successful operation of the entire hardware system with the first

beryllium sample, extensive testing of the system was done using a relatively inexpensive ’’dummy" steel sample. The first trial loadings and

interferometer adjustments quickly led to a new design for the optical flat

adjustable mount. Following this improvement, the steel sample was repeatedly loaded until the techniques were adequate to provide satisfactory,

reproducible interference pattern.

Next, the photographic data system was tested and fine tuned. A series of

test photographs were made to provide data for selection and aperture and

exposure time. Since one of the important requirements of the system is

the ability to traverse from one sample station to another, we tested our ability to travel away from and back to the station with the steel sample in

it. This system seems to work very well, but depends strongly upon proper,

careful initial alignment of the load frames.

After the first beryllium sample was loaded, the testing of this system

continued. We repeatedly traversed between the steel sample and the beryllium

sample over an extended period of time without major difficulty.

SAMPLES

Two beryllium samples have now been loaded. The first had a dead weight of

3 kilograms, and the second load was 10 kilograms. Over 300 data photographs

have been taken of the changing interference pattern since the first sample was

loaded. We have established our own in-house capability to do the photographic processing work to be certain that no data is lost.

The only problems that have been encountered in the data collection are

failures of the room temperature control. Sudden temperature shifts apparently introduce a change in the optical wedge angle, which causes a major change

in the interference pattern. However, the steel reference flat directly

measures this change, so it is not of major concern. (Such possible changes

were the reason for originally including the reference flat in the design.)

SOFTWARE

Software development and testing has continued. It has continued to be

hampered by limited access time on the image analysis system. The original

software has been considerably improved by structuring the code more strongly,

modularizing its function, and incorporating a good deal of fault tolerance.
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The necessary analysis software unfortunately exceeded the memory capacity of

the image analysis computer in August 1981. While this is not a major

problem, it has led to a major delay, the likelihood of this was foreseen at

the beginning of the software development, thus leading us to write the

programs in a modular form. It would then be possible to segment the code

into several smaller sequential programs, each of which required much less

memory capacity. This segmentation is straightforward but labor intensive.

The image analysis facility was planned to have a new computer installed in

September with improved speed and more memory. We decided to delay segmentation since the effort would probably be obsolete before it was completed.

However, the installation of the new computer has been pushed back by a month

every month since September, and we are still waiting. If it is not available

by February, we will proceed with program segmentation regardless of March

promises.

REPORT

A review report oji the biaxial system was prepared early in the year for

archival purposes.'^ It briefly reviewed the details of the project requirements, hardware design to data, software approach, and functional overview of

the entire data acquisition and processing system.

1. T. Charlton and R. Hocken: Review of Biaxial Beryllium Microcreep Test

System: Status Report, December, 1980.

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December 1981

1

PART B

i APPENDIX I - SPECIMEN INVENTORY

i MICROMECHANICAL PROPERTIES OF BERYLLIUM

AND OTHER INSTRUMENT MATERIALS

ii'

TESTING

SYSTEM

SPECIME N DESCRIPTION MATERIAL QUANTITY

SHAPE SIZE

OneDimension

Hoi low

Cylinder

4 - in. long

0.400 - in. diam.

0.25 - in. bore.

1-400

beryl 1 ium

1 ready for testi

4 - in. long

7/16 in. outside diam.

0.25 - in. bore.

INVAR 4 in test

1-400

beryl 1 ium

4 ready for testi

Hoi low

Cyl inder

4 - in. long

0.9 - in. diam.

0.25 - in. bore.

Steel Gage Block

Standard

1 in test

Square

Parallel - Apiped

4 - in. long

1 - in. square section

0.25 - in. bore

Cervit Standard 1 in test

Biaxial

1

i

Di sk 2 - in. diam.

1/8 - in. thick

1-400

beryllium

2 in test

2 on hand

2 in preparation

at C. S. Draper L Cambridge, MA.
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