Astm stp 888 1986

H., "Use of the Disk Bend Test to Assess Irradiation Performance of Structural Alloys," The Use of Small-Scale Specimens for Testing Irradiated Material, ASTM STP 888, W.. Specimens of

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The Use of

Small-Scale Specimens for

Testing Irradiated IVIaterial

A symposium sponsored by ASTM Committee E-10

on Nuclear Technology and Applications

Albuquerque, N.M., 23 Sept 1983

ASTM SPECIAL TECHNICAL PUBLICATION 888

W R Corwin, Oak Ridge National Laboratory, and G E Lucas, University of California - Santa Barbara, editors

ASTM Publication Code Number (PCN) 04-888000-35

1916 Race Street, Philadelphia, Pa 19103

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Libraiy of Congress Cataloging-in-Pnblication Data

The Use of small-scale specimens for testing irradiated material

(ASTM special technical publication; 888)

"A symposium sponsored by ASTM Committee E-10 on

Nuclear Technology and Applications, Albuquerque, N.M.,

23 Sept 1983."

Includes bibliographies and index

1 Materials—Effect of radiation

on—Testing-Congresses I Corwin, W R II Lucas, Glenn E.,

1951- III ASTM Committee on Nuclear Technology

and Applications IV Series

TA418.6.U84 1986 620.1'1228 85-27487

ISBN 0-8031-0440-5

Library of Congress Catalog Card Number: 85-27487

NOTE The Society is not responsible, as a body, for the statements and opinions advanced in this publication

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Foreword

The ASTM Symposium on The Use of Nonstandard Subsized Specimens for

Irradiated Testing was held in Albuquerque, New Mexico, on 23 September

1983 Its sponsor was ASTM Committee E-10 on Nuclear Technology and

Ap-plications W R Corwin, Oak Ridge National Laboratory, and G E Lucas,

University of California - Santa Barbara, served as symposium chairmen and

have edited this publication

The title of this volume has been changed slightly from that of the symposium

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Related ASTM Publications

Effects of Radiation on Materials—12th International Symposium, STP 870

(1985), 04-870000-35

Zirconium in the Nuclear Industry: Sixth International Symposium, STP 824

(1984), 04-824000-35

Radiation Embrittlement and Surveillance of Nuclear Reactor Pressure

Ves-sels: An International Study, STP 819 (1983), 04-819000-35

Creep of Zirconium Alloys in Nuclear Reactors, STP 815 (1983), 04-815000-35

Status of USA Nuclear Reactor Pressure Vessel Surveillance for Radiation

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A Note of Appreciation

to Reviewers

The quality of the papers that appear in this publication reflects not only the

obvious efforts of the authors but also the unheralded, though essential, work

of the reviewers On behalf of ASTM we acknowledge with appreciation their

dedication to high professional standards and their sacrifice of time and effort

ASTM Committee on Publications

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ASTM Editorial Staff

Allan S Kleinberg Janet R Schroeder Kathleen A Greene Bill Benzing

Downloaded/printed by

University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized.

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Contents

Introduction

STRENGTH AND DUCTILITY Use of the Disk Bend Test to Assess Irradiation Performance of

Structural Alloys—M L HAMILTON AND F H HUANG 5

Miniaturized Disk Bend Test Technique Development and

Application—M P MANAHAN, A E BROWNING, A S ARGON,

AND O K H A R L I N G 17

The MTT Miniaturized Disk Bend Test—o K HARLING, M LEE,

D-S SOHN, G KOHSE, AND C W LAU 5 0

Disk-Bend Ductility Tests for Irradiated Materials—R L KLUEH AND

D N BRASKI 6 6

General Discussion: Miniaturized Disk Bend Test 83

Development of Small Punch Tests for Ductile-Brittle Transition

Temperature Measurement of Temper Embrittled Ni-Cr

Steels—J.-M BAIK, I KAMEDA, AND O BUCK 9 2

Discussion 110

Shear Punch and MScrohardness Tests for Strength and Ductility

Measurements—G E LUCAS, G R ODETTE, AND

I W SHECKHERD 112

Discussion 139

Low-Load Microhardness Changes in 14-MeV Neutron Irradiated

Copper Alloys—s i ZINKLE AND G L KULCINSKI 141

Discussion 159

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Effects of Specimen Thickness and Grain Size on the Mechanical

Properties of Types 304 and 316 Austenitic Stainless Steel—

N IGATA, K MIYAHARA, T UDA, AND S ASADA 161

Failure Strain for Irradiated 2^aloy Based on Subsized Specimen

Testing and Analysis—R B ADAMSON, S B WISNER,

R P TUCKER, AND R A RAND 171

Discussion 185

Wire Tensile Testing for Radiation-Hardening Experiments—

E R BRADLEY AND R H JONES 186

Discussion 200

D e s ^ and Use of Nonstandard Tensile Specimens for Irradiated

Materials Testing—N F PANAYOTOU, S D ATKIN,

R J PUIGH, A N D B A C H I N 2 0 1

Discussion 219

Comparison of Mechanical Properties in Thin Specimens of Stainless

Steel with Bulk Material Behavior—D G RICKERBY, P FENICI,

p JUNG, G PIATTI, A N D P SCHILLER 2 2 0

Discussion 231

A Miniaturized Mechanical Testing System for Small-Scale Specimen

Testing—S.-P HANNULA, J WANAGEL, AND C.-Y LI 233

Discussion 250

Post-Irradiation Creep Properties of Cold-Worked 316 Stainless Steel

As Measured with Small Creep Specimens—

w VANDERMEULEN, M SNYKERS, AND PH VAN ASBHOECK 252

FATIGUE AND FRACTURE Miniature Center-Cracked-Tension Specimen for Fatigue Crack

Growth Testhig—A M ERMI AND L A IAMES 261

Use of Subsize Fatigue Specimens for Reactor Irradiation Testing—

K C LIU AND M L GROSSBECK 2 7 6

Discussion 289

Use of Subsized Specimens for Evaluating the Fracture Toughness of

Irradiated Materials—F H HUANG 290

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Subsized Bend and Charpy V-Notch Specimens for Irradiated

Testing—G E LUCAS, G R ODETTE, I W SHECKHERD,

p M C C O N N E L L , A N D I PERRIN 3 0 5

Discussion 324

Effect of Specimen Size and Material Condition on the Charpy

Impact Properties of 9Cr-lMo-V-Nb Steel—w R CORWIN AND

A M HOUGLAND 3 2 5

Discussion 337

Specimen-Size Considerations in Craclc-Arrest Testing of Irradiated

RPV Steels—c w MARSCHALL, A R ROSENFIELD, AND

M p LANDOW 339

Experience in Subsized Specimen Testing—p MCCONNELL,

J W S H E C K H E R D , J S PERRIN, AND R A WULLAERT 3 5 3

Summary 369

Index 371

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STP888-EB/Feb 1986

Introduction

Attempts to miniaturize mechanical test specimens, particularly for testing

irradiated materials, are certainly not new Limited space in materials test

reactors, concern about gamma heating or fluence gradients in large

speci-mens, and dose to personnel in post-irradiation testing have all been

motiva-tions for reducing specimen size In addition, limited material availability or

test machine capacity (e.g., in the case of fracture toughness testing) and

mi-crostructural gradients in thick sections have historically provided impetus

for reducing specimen size in testing materials in general However, recent

efforts to develop materials for nuclear/MJ/OM reactors have provided a much

increased interest in scaling down mechanical test specimen sizes

The current fusion reactor materials development program, both in the

United States and worldwide, is hampered by the lack of a prototypic

irradia-tion environment in which to test candidate materials This necessitates a

de-velopment program with the following characteristics: (1) heavy reliance on

fission-reactor-based irradiation data, (2) development of a correlation

meth-odology based on a fundamental understanding of radiation damage and

re-sulting property changes, (3) extrapolation of the correlation methodology to

the fusion regime, and (4) verification of extrapolated predictions by

compar-ison with 14 MeV neutron irradiation data To accomplish this last step in the

near future will require reliance on accelerator-based high energy neutron

sources which are quite limited in irradiation volume This in turn absolutely

requires the use of low-volume specimens and the development of

correspond-ing techniques to extract useful properties from such specimens

Consequently, a number of programs have been engaged in developing

such techniques Indeed, rapid progress has been made on a host of

tech-niques providing a wide range of measured properties, and interest in these

techniques has become relatively widespread As a result, concern has arisen

that techniques might be developed and applied without adequate

coordina-tion among users, leading to unnecessary confusion, erroneous data, and

du-plication of effort A task group was thus formed under the auspices of ASTM

Subcommittee E10.02 on Behavior and Use of Metallic Materials in Nuclear

Systems to consider whether a set of recommended practices for individual

small-specimen techniques might be useful and, if so, to write such practices

One of the first decisions of the task group was that the time was

appropri-ate to hold a symposium on small-specimen testing It was felt that this would

serve as an initial milestone in the development of these tests, and that the

Copyright' 1986 b y A S T M International www.astm.org

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2 SMALL-SCALE SPECIMENS FOR TESTING IRRADIATED MATERIAL

resulting publication could be used to help address questions concerning

rec-ommended practices As members of this task group, we agreed to organize

such a symposium and to edit the contributed papers The symposium was

held in Albuquerque, New Mexico, on 23 September 1983 and consisted of

parallel morning and afternoon sessions Full-length papers were submitted

following the symposium and were thoroughly reviewed The papers

con-tained in this publication represent the culmination of this effort It is our

hope and belief that these papers will be of significant use in advancing the

technology of small-specimen testing

W R Corwin

Metallurgical Engineer, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee; symposium chairman and editor

G E Lucas

Associate Professor, Department of Chemical and Nuclear Engineering, University of Cal- ifornia, Santa Barbara, California; symposium chairman and editor

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Strength and Ductility

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M L Hamilton^ and F H Huang^

Use of the Disk Bend Test to Assess

Irradiation Performance of Structural

Alloys

REFERENCE: Hamilton, M L and Huang, F H., "Use of the Disk Bend Test to Assess

Irradiation Performance of Structural Alloys," The Use of Small-Scale Specimens for

Testing Irradiated Material, ASTM STP 888, W R Corwin and G E Lucas, Eds.,

American Society for Testing and Materials, Philadelphia, 1986, pp 5-16

ABSTRACT: The disk bend test has been a valuable technique for rapid evaluation of the

ductility of a large number of alloys under consideration for use as structural materials in

the breeder and fusion reactor programs The test employs the 3-mm-diameter,

0.3-mm-thick microscopy and density disk specimen, conserving valuable experimental volume in

the limited reactor space available

The test involves bending the disk symmetrically about the center, producing a simple,

axisymmetric stress state Experimental results are in agreement with a theoretical

analy-sis of the bend configuration The advantages and limitations of the technique are

dis-cussed

The test has shown that commercial precipitation-strengthened alloys and the Path B

alloys of the U.S Fusion Program exhibit unacceptably low ductilities following

irradia-tion This was demonstrated for a number of alloys, in a variety of thermomechanical

conditions, including cold worked, cold worked and aged, and solution treated and aged

KEY WORDS: disk bend, Path B alloys, nickel-base alloys

Irradiation in a fast-neutron environment is known to cause a significant

reduction in the ductility of many types of alloys, including austenitic [/],

precipitation-hardened [2], and ferritic [3] stainless steels To ensure the

safe operation of future fusion and fast breeder reactors, it is essential that a

finite, but modest, residual ductility is retained by the relevant structural

al-loys Experience with cold-worked Type 316 stainless steel (for example, the

reference material for the Fast Flux Test Facility) has shown that the ductility

following neutron irradiation is typically greater than 1 % High swelling and

'Westinghouse Hanford Company, Richland, WA 99352

Trang 15

irradiation creep, however, limit this material to fluences on the order of 1 X

1 0 2 ' n / m 2 ( £ ' > 0.1 MeV)

Ambitious alloy development programs have been pursued within both the

breeder and fusion programs in an effort to extend the high fluence capability

of the relevant structural materials, thereby attaining more economical

reac-tor operation [2] The initial stages of these efforts required irradiation of

many alloy variants because of the sensitivity of creep and swelling to minor

element composition changes Under the auspices of the fusion and breeder

programs, hundreds of alloy variants have been irradiated to examine their

swelling behavior The high-nickel precipitation hardened alloys in particular

appeared to offer excellent swelling resistance [4] and received a strong

em-phasis in both irradiation programs It soon became clear, however, that alloy

conditions having good swelling resistance might not retain adequate

me-chanical behavior following irradiation

Space in high flux portions of most reactors is quite limited Any technique

that permitted multiple use of a single specimen would therefore conserve

valuable irradiation space Techniques were developed to obtain density

mea-surements on miniature disk specimens The disk geometry was tailored for

transmission electron microscopy (TEM), being small enough to handle after

irradiation with minimal shielding and requiring no sectioning prior to

thin-ning for microscopy The disk bend test was originally developed [5] as a

means of screening, on the basis of ductility, the large number of alloys being

irradiated as small TEM disks A single specimen was first used to measure

density to assess swelling resistance, and then used to measure residual

duc-tility

The Path B alloys are precipitation hardenable alloys considered for

possi-ble structural applications in the fusion first-wall/blanket, based on the

ex-cellent high temperature strength and creep resistance exhibited by this alloy

class under the breeder alloy development program Matrix hardening arises

from the formation of 7 ' or 7 ' / 7 " They were irradiated in the higher flux

isotope reactor (HFIR) in various thermomechanical conditions, including

cold worked (CW), cold worked and aged (CWA), and solution treated and

aged (STA) It was anticipated that the helium levels produced during HFIR

irradiation would significantly affect the microstructure and ductility of the

alloys The disk bend technique was therefore used to evaluate their

postirra-diation ductility Detailed microstructural examinations were performed [6]

to determine the mechanism(s) responsible for the reduction in ductility

Experimental Procedure

A detailed description of the compositions, thermomechanical conditions,

and irradiation conditions of the Path B alloys is given in Tables 1,2, and 3

Alloy B2 is similar to Nimonic PE16, while Alloy B3 is similar to Inconel 706

Specimens of the Path B alloys were irradiated at four temperatures in HFIR

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HAMILTON AND HUANG ON DISK BEND TEST

HI

32 B3

7 ' / 7 " -strengthened B4

Nickel base B6

Ni Cr Mo Nb Ti Al C Si 25.0 10.0 1.0 3.0 1.5 0.03 0.3 40.0 12.0 3.0 1.5 1.5 0.03 0.3 30.0 12.0 2.0 2.0 0.5 0.03 0.03 40.0 12.0 3.0 1.8 0.3 0.03 0.3 75.0 15.0 1.0 2.5 1.5 0.03 0.3

Mn B 1.0 0.001 0.2 0.001 1.0 0.001 0.2 0.001 0.2 0.001

TABLE 2— Thermomechanical treatments of the Path B alloys.'

L5 L6

LX L7

1025°C/5 min/AC + 30% CW 1025°C/5 min/AC + 30% CW + 800°C/8 h/AC 1025°C/5 min/AC + 30% CW + 750'=C/8 h/AC 1025°C/5 min/AC + 800°C/8 h/AC

1025°C/5 min/AC + 30% CW 1025°C/5 min/AC + 30% CW + 750°C/8 h/AC

1025°C/5 min/AC + 30% CW + 700°C/8 h/AC

1025°C/5 min/AC + 30% CW 1025°C/5 min/AC + 30% CW + 750°C/8 h/AC 1025°C/5 min/AC -(- 30% CW + 700°C/8 h/AC 1025°C/5 min/AC -1- 850°C/3 h/AC

+ 720°C/8 h/FC to 620°C/10 additional h/AC 1025°C/5 min/AC + 40% CW

1025°C/5 min/AC + 40% CW -1- 800°C/8 h/AC 1025°C/5 min/AC + 40% CW -1- 750°C/8 h/AC

Zr 0.05 0.05 0.05 0.05 0.05

"AC = air cool; FC = furnace cool; CW = cold-worked

TABLE 3—Dose and helium accumulation of the Path B alloys

B-1 B-2 B-3 B-4 B-6

300°C 7.6 dpa

596 ppm 4.4 dpa

455 ppm 7.6 dpa

714 ppm 4.4 dpa

455 ppm 4.4 dpa

853 ppm

400°C 7.6 dpa

596 ppm 4.4 dpa

455 ppm 7.6 dpa

714 ppm 4.4 dpa

455 ppm 4.4 dpa

853 ppm

500°C 9.2 dpa

852 ppm 9.2 dpa

1363 ppm 9.2 dpa

1021 ppm 9.2 dpa

1363 ppm 9.2 dpa

2553 ppm

600°C 8.5 dpa

723 ppm

8.5 dpa

866 ppm 9.2 dpa

1263 ppm 9.2 dpa

2553 ppm

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in the form of the 3-mm-diameter TEM disks Tests were conducted at either

the irradiation temperature or at 110°C above the irradiation temperature, a

condition where a minimum in ductility has previously been observed for

these types of alloys

Although the development of the disk bend test is described elsewhere [5],

a brief description of the technique is in order The test consists of bending

symmetrically with a hemispherical punch of radius 1.588 mm (0.0625 in.) at

the center of the specimen, producing a simple axisymmetric stress state The

test fixture provides uniform support around the edge of the disk, preventing

shear deformation or breakage at the edges during a test (Fig 1) The edge of

the disk is supported by a recessed lip in the die cavity, which has the same

dimensions as the hemispherical punch The disks are tested in an air furnace

using a hydraulically driven modified MTS frame The punch is forced

against the specimen at a rate of 0.005 cm/min until failure occurs Load and

displacement are monitored continuously; alignment of the specimen and

punch is maintained by two guide rods that mesh with holes in the die Disks

range from 0.23 to 0.31 mm (0.009 to 0.012 in.) thick with a minimum of

about 10 grains across the thickness

The original developmental tests on heat-treated, unirradiated

molybde-FIG 1—Test fixture schematic

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HAMILTON AND HUANG ON DISK BEND TEST 9

num showed clearly that failure of the disks was signaled by a discontinuity in

the load deflection curve (Fig 2) This indicated that ductility could be

as-sessed strictly from the load-deflection curves without recourse to expensive

post-test profilometry Determination of the strain from the load-deflection

curve, however, is not as straightforward as in a tensile test For brittle

mate-rials exhibiting only small strains before failure, the following nonlinear

equation relates ductility and deflection [5]:

tw

where t and a are the thickness and radius of the disk, and w and e are the

deflection and the ductility The original results showed that good agreement

was obtained for low strains with the theoretical analysis of the bend

configu-ration

Specimen failure occurs along radial cracks emanating from the disks'

cen-ters Since some irradiated disks may fracture shortly beyond the elastic

de-formation, a characteristic change in slope in the load-deflection pattern can

be used to detect failure Since the deflection of the disk varies as the cube of

the thickness, the load versus crack extension curve will be strongly altered

with the outside fibers of the disk first crack The criterion for ductility is then

the strain at fracture, analogous to the total elongation in a tensile test The

->

DEFLECTION (mm x 10-2)

2 4 6 8 10 12 14 16

I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 TEST TEMP = 2S°C

Trang 19

« o

O -H c3 <u vi

Trang 20

ductility of the test specimen can be calculated from the deflection at which a

slope change takes place using Eq 1

This approach to the estimation of ductility from disk specimens was

veri-fied by comparing the bend and tensile ductilities on identical material Disks

were fabricated from the grip ends of previously tested tensile specimens

Sat-isfactory correlation between the bend and tensile ductilities indicated that

the criterion for estimating ductility was acceptable

Results

All the Path B alloys exhibited low ductility at temperatures ranging from

300 to 700°C (572 to 1292°F) The reported values of ductility (Table 4) were

calculated at the point of maximum load, which provides an indication of the

point at which crack propagation begins At temperatures above about

500°C, the ductility was less than 1% for all alloy conditions tested This

"ductility trough" phenomenon is common in nickel-base alloys, which

typi-cally exhibit an increase in ductility as temperature increases A severe drop

in ductility was observed not only in the CW condition of all the Path B alloys

(Fig 3) but also in the CWA condition of Alloys Bl, B2, B3, and B4 (Fig 4)

Arrows in these figures designate minimum values of ductility obtained in

tests which were terminated before the observation of any visible evidence of

fracture on the load-displacement traces

The high-nickel alloy B6 in the CWA condition was the only alloy which did

not show a severe drop in ductility in the temperature range of the ductility

trough (Fig 5), although B6 was expected to accumulate the most helium

during irradiation because of its higher nickel content

700

FIG 3—Disk bend ductility of cold-worked Path B alloys tested at the irradiation

tempera-ture

Trang 21

• 84 (LL)

\„,^

k_^ ,

200 300 400 500 600 TEST TEMPERATURE, °C

FIG 5—Disk bend ductility of cold-worked and aged Alloy B6 tested at the irradiation

tem-perature and 110°C above the irradiation temtem-perature

Microstructural studies indicated that the low post-irradiation ductility of

the Path B alloys results from the simultaneous existence of a strong matrix

and weak grain boundaries [6] Helium bubbles and various other precipitate

structures weaken the grain boundaries, while the matrix is strengthened in

each of the alloys by the formulation of 7 ' or Y ' / Y * precipitates,

radiation-induced faulted loops, and small helium bubbles

Trang 22

Discussion

For high strength materials susceptible to severe irradiation

embrittle-ment, Eq 1 was found to be a simple and accurate means of relating the

de-flection of the TEM disk specimen to the strain The development of the

equations from which ductility is calculated was based on the assumption that

only small strains were involved Thus valid ductility data are obtained for

strains of only a few percent If unacceptable errors result from using Eq 1, a

deflection-to-strain conversion is needed to compute accurately the ductility

of the disk specimen

Since the ductility of irradiated materials is expected to be small, it is

rea-sonable to assume that the stress-strain behavior is bilinear [ 7] For ductile

materials, however, bilinear stress-strain behavior is an oversimplification A

power-law relation may therefore be required for ductile materials

Depend-ing on how closely the power law describes the tensile behavior of the

mate-rial, reasonably accurate results may still be obtained through the analysis of

stress and strain presented in the Appendix for bending of a circular plate

[5]

In some situations, particularly for materials exhibiting large ductility and

highly nonlinear tensile behavior, finite element methods [8] may eventually

be capable of extracting mechanical behavior information from the

load-deflection curve of disk specimens A great deal of care must be taken,

how-ever, when testing TEM disk specimens of ductile materials One potential

problem is specimen slippage that may occur along the support at large

de-flections The analysis of bending in a circular plate must be corrected for any

clamping forces applied between the support and the specimen to prevent

such slippage from occurring

Conclusions

The test has been extremely useful as a screening device when the major

criterion for an alloy was its residual ductility following irradiation The test

provides rapidly, easily obtained information on whether an alloy has

ade-quate post-irradiation ductility for a particular application In addition, this

information is obtained on multipurpose specimens which are exceedingly

economical of the limited experimental reactor volumes available

The disk bend technique characterized the ductility of Path B alloys

irradi-ated in HFIR to a dose of —10 dpa At test temperatures above 500°C

(932°F) the post-irradiation ductility is less than 1% for all alloy conditions

tested

Trang 23

APPENDIX

Procedure for Conversion of Deflection to Strain for tlie Bending of a Circular Plate

The assumption is made that the stress-strain curve of the material is composed of two straight lines:

a = Ee for e < e, (Je + E'(e — e^) for e > 6^

(2) (3)

where E and E' are the slopes of the two segments, and a^ is the stress at the yield

ir.t

Z

Pr.e er.e + ir.e (6)

Pe<P-r

FIG 6—Plastic deformation of a circular plate

Trang 24

er.e — (cr,» — va,r)/E (7)

Or.) = ZE (Upr,» + v/pe,,)/{\ - V^) - E(ir,B + m,rV(^ " v'^) ( 8 )

where i* is Poisson's ratio, E is Young's modulus, Pr is the curvature in the plane of a

meridian, and pe is the curvature at the intersection of the meridional plane and a

plane normal to it The curvature of the deflected plate (Fig 6) can be related to the

Combining Eqs 8,9, and 11, M , and Me are solved for functions of w and ệj

Substi-tuting these into Eq 10, dw/dr can be solved [Eq A7 in Ref 5]

References

[/] Fish, R L and Watrous, J D., "Effect of Fast Reactor Irradiation on the Tensile

Proper-ties of 20 Percent Cold-Worked Type 316 Stainless Steel," in Irradiation Effects on the

Microstructure and Properties of Metal ASTM STP611, American Society for Testing and

Materials, Philadelphia, 1976, pp 91-100

[2] Vaidyanathan, S., Lauritzen, T., and Bell, W L., "Irradiation Embrittlement in Source

Austenitic Superalloys," in Effects of Radiation on Materials: Eleventh Conferencẹ

ASTM STP 782 H R Brager and 1 S Perrin, Eds., American Society for Testing and

Materials, Philadelphia, 1982, pp 619-635

[3] Klueh, R L., Vitek, J M., and Grossbeck, M L., in "Nickel-Doped Ferritic (Martensitic)

Steels for Fusion Reactor Irradiation Tempering Behavior and Irradiated Tensile

Proper-ties," in Effects of Radiation on Materials: Eleventh Conferencẹ ASTM STP 782 H R

Brager and J S Perrin, Eds., American Society for Testing and Materials, Philadelphia,

1982, pp 648-664

{4} Johnston, W G., Lauritzen, T., Rosolowski, J H., and Turkalo, Ạ M., "An

Experimen-tal Survey of Swelling in Commercial Fe-Cr-Ni Alloys Bombarded with 5 MeV Ni Ions,"

Journal of Nuclear Materials, Vol 54, 1974, p 24

[5] Huang, F H., Hamilton, M L., and Wire, G L., "Bend Testing for Miniature Disks,"

Nuclear Technologỵ Vol 57, 1982, p 234

[6] Yang, W J S and Hamilton, M L., "The Ductility and Microstructure of

Trang 25

Precipitation-16 SMALL-SCALE SPECIMENS FOR TESTING IRRADIATED MATERIAL

Strengthened Alloys Irradiated in HFIR," in Proceedings, Third Topical Meeting on

Fu-sion Reactor Materials, 19-22 Sept 1983, Albuquerque, N.M

[7] Dieter, G E., "Introduction to Ductility," in Ductility, American Society for Metals,

Metals Park, Ohio, 1968, p 1

[8] Manahan, M., "The Development of a Miniaturized Disk Bend Test for Determination of

Post-Irradiation Mechanical Behavior," Ph.D thesis, Massachusetts Institute of

Technol-ogy, Cambridge, Mass., 1982

Trang 26

M P Manahan, ^ A E Browning, ^ A S Argon, ^

and O K Hurling^

Miniaturized Disk Bend Test

Technique Developnnent and

Application

REFERENCE: Manahan, M P., Browning, A E., Argon, A S., and Marling, O K.,

"Miniaturized Disic Bend Test Technique Development and Application," The Use of

Small-Scale Specimens for Testing Irradiated Material, ASTM STP 888, W R Corwin

and G E Lucas, Eds., American Society for Testing and Materials, Philadelphia, 1986,

pp 17-49

ABSTRACT: The objective of miniaturized specimen technology is to enable the

charac-terization of mechanical behavior while using a greatly reduced or minimum volume of

material The significance of this technology is obvious to the nuclear industry where

neu-tron irradiation space is limited and irradiation costs scale with specimen volume In

ad-dition, the substantial advantages resulting from application of this technology in

non-nuclear industries are only beginning to be realized

The initial development of a miniaturized disk bend test (MDBT) for extraction of

post-irradiation mechanical behavior information from disk-shaped specimens no larger

than transmission electron microscopy samples is described Central loading with a

hemi-spherically tipped punch is used to measure load/deflection curves to fracture These

load/deflection curves are simulated using finite element analysis This approach to

min-iature mechanical property testing is shown to offer the potential for the derivation of

uniaxial flow properties

This paper primarily emphasizes the development of test techniques and procedures;

however, results for the determination of uniaxial tensile behavior are presented to

dem-onstrate the validity of the basic methodology Recommended techniques for specimen

design, specimen preparation, experimental design, experimental implementation, and

data analysis are presented

KEY WORDS: mechanical behavior, miniature specimens, uniaxial tensile behavior,

scanning electron, microscopy, microstructure, continuum mechanics, finite element

method, electrical discharge machining, lapping

'Senior Research Scientist, and Candidate for M S at the Ohio State University, respectively,

Battelle Columbus Laboratories, Columbus, OH 43201

^Professor of Mechanical Engineering and Director of Nuclear Reactor Laboratory,

respec-tively, Massachusetts Institute of Technology, Cambridge, MA 02139

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1 8 SMALL-SCALE SPECIMENS FOR TESTING IRRADIATED MATERIAL

The primary focus of this paper is on the development of the Miniaturized

Disk Bend Test (MDBT) techniques for the determination of uniaxial tensile

behavior, and many of the techniques and procedures discussed should be

applicable to a wide variety of miniature specimen applications Actual test

results are presented only to help illustrate the validity of the methodology In

this paper we document the initial development of the MDBT which was

car-ried out at MIT and some further work done at Battelle-Columbus In doing

this we have borrowed extensively from our previous publications [1-4],

in-cluding the figures and tables used here The results of continuing work at

MIT are the subject of another paper presented at this symposium [4a]

The problem to be addressed is that of determining mechanical behavior

from specimens which are substantially smaller than the conventional

speci-mens currently in use The initial impetus for the development of

miniatur-ized specimen technology (MST) came from the need to test irradiated

mate-rials using as little material as possible This is desirable because neutron

irradiation space for materials investigations is limited and costly In

addi-tion, in many future fusion reactor alloy development irradiations, such as

those to be conducted in the Rotating Target Neutron Source (RTNS)-II

facil-ity and potentially in the Fusion Materials Irradiation Test (FMIT) facilfacil-ity if

ever built, it will only be feasible to irradiate miniature specimens It was

recognized from the outset that MST would be applicable to materials

investi-gations both in nuclear technologies and in non-nuclear technologies

requir-ing mechanical behavior characterization from a very small volume of

mate-rial (e.g., failure analysis and rapid solidification technology)

Research to date [ 1-4] at MIT on miniature tensile behavior determination

has been primarily focused on disk-shaped specimens (nominally 3.0 by 0.25

mm) which are no larger than those used for transmission electron

micros-copy Figure 1 graphically depicts the size scale involved by comparing

minia-turized disk bend test (MDBT) specimens with a more conventional small

post-irradiation uniaxial tensile specimen These MDBT specimens are

gen-erally about 500 times smaller than the more conventional uniaxial tensile

specimens currently used for post-irradiation testing, and about an order of

magnitude smaller than most miniaturized tensile specimens Since MDBT

specimens are quite small, a nonstandard loading configuration is used As a

result, finite element analysis must usually be performed to convert the

exper-imentally determined central load/deflection curves into stress/strain and

other useful engineering information

There are three principal conceptual innovative aspects inherent in our

so-lution to the problem of obtaining mechanical behavior using miniature

spec-imens:

1 Mechanical behavior specimens are used that are significantly smaller

than those currently in use or that are significantly smaller than the in-service

components from which they are cut

2 An appropriate loading configuration is chosen to accommodate the

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MANAHAN ET AL ON MINIATURIZED DISK BEND TECHNIQUE 19

One Snudi

J:*.'

FIG i^-Miniaturized disk bend test specimens compared with one small conventional

post-irradiation tensile specimen The volume of one small tensile specimen is equal to the volume of

484 miniaturized disk bend test specimens

size scale involved or to represent the actual in-service loading In practice,

bending is used to extract mechanical behavior as opposed to the more

stan-dard approach of using uniaxial tension/compression loading requiring

grip-ping extensions

3 The finite element method is used to extract useful engineering

informa-tion from the experimental data or to determine the desired experimental

pa-rameter ranges

General Methodology

The recommended experimental configuration for miniature disk bend

testing consists of a simply supported disk which irests in a cylindrical die and

a hemispherical punch which presses the disk into the cavity as shown in the

inset of Fig 2 During the test, the applied load of the punch versus

displace-ment under constant impression velocity is measured

In order to analyze the MDBT using the finite element method, the

bound-ary conditions must be accurately modeled A new boundbound-ary condition model

capable of analyzing intermittent frictional contact has been developed for

this purpose [/] The strain fields present in the MDBT are highly

nonuni-form, unlike the more conventional uniaxial tensile strain fields Therefore

precise three-dimensional boundary condition modeling is essential to set up

the correct strain gradients in the plate The model accounts for nonuniform

strain as well as the nonlinear boundary conditions with shifting frictional

contacts The validity of the MDBT methodology has been examined for one

material with well characterized mechanical behavior using small strain finite

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DMiil ar Lending

FIG 2—Actual miniaturized disk bend test apparatus installed in environmental chamber

and schematic of miniaturized disk bend test section showing simply supported disk under

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MANAHAN ET AL ON MINIATURIZED DISK BEND TECHNIQUE 2 1

element analysis [ / ] While the results are promising, further tests are needed

to qualify the MDBT approach fully for other materials

The basic data inversion strategy for the near term for materials that

be-have isotropically is as follows:

1 Assume several flow curves that bracket the flow curve of the material

being investigated

2 Implement the finite element code and generate the central

load/deflec-tion curves for the various flow curves of Step 1

3 Compare the finite element simulation of the experiment with the

exper-imentally measured data Repeat Steps 1 and 2 until a calculated central

load/deflection curve falls within the experimental reproducibility band

This procedure is illustrated in a flow chart format in Fig 3 This is a near

term strategy because in time the finite element data base will become

suffi-ciently large, for a standardized specimen and loading geometry, that no

fur-ther finite element runs will be necessary for a given material Therefore an

alternative fourth step would be:

4 Interpolation of calculated load/deflection curves for a measured load/

deflection curve to determine the stress/strain curve of the material being

tested

The primary advantage of using finite element analysis for data inversion,

as opposed to small strain analytical equations, is that the deformation

re-sponse of the material can be measured for materials that exhibit large strains

to fracture (i.e., ductile versus brittle materials) Also, in many geometries,

finite element analysis is the only method of analysis available capable of

dealing with complex loading problems In general, the finite element

method is much more versatile and appropriate than small strain analytical

methods; therefore incorporation of the finite element method into the

minia-ture specimen test methodology produces a far more powerful tool

This section provides the background and overview for the MDBT The

following sections of the paper discuss specific aspects of the test

Specimen Design Considerations

In choosing the specimen size and loading configuration for the

determina-tion of tensile behavior using the MDBT, careful consideradetermina-tion must be given

to several important factors, such as:

1 Scale of material microstructure

2 Behavior approaching that of a continuum in ail directions

3 Amount of material or irradiation space, or both, available

4 Desired stress state during the test

5 Plastic instabilities

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FIG 3—Flowchart of the basic data inversion strategy

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MANAHAN ET AL ON MINIATURIZED DISK BEND TECHNIQUE 23

The first step in any miniature mechanical behavior specimen design is to

characterize the material microstructure The key information to be

deter-mined includes variables such as average and maximum grain sizes, average

and maximum particle sizes, and degree of anisotropy All the

microstruc-tural variables are then analyzed to determine the minimum volume and

smallest dimension sufficient to satisfy continuum behavior in all directions

In large strain deformation problems precise criteria for a minimum

dimen-sion to justify continuum treatment are difficult to give since they depend on

the imposed constraints, the degree of texture evolution, etc A desirable

cri-terion might be that the minimum dimension be no less than ten times the

largest microstructural heterogeneity Since MST was originally developed to

test samples prepared from small lots of material or for irradiation studies,

the next step is to ensure that the continuum requirements do not violate the

practical limits of the application The desired stress state in the specimen

during the test must be considered so that the optimum loading configuration

can be adopted Often it is desirable to simulate the anticipated in-service

loading conditions to obtain data which are more representative of the final

in-service application of the material Plastic instabilities will be considered

in detail in the following section

As a result of these considerations, we chose a simply supported disk 3 mm

in diameter and 0.25 mm thick to test irradiated fusion first-wall candidate

alloys A biaxial stress field was achieved by loading the disks transversely

using a hemispherical punch

Specimen Preparation Tecliniques

Specimen Machining

Because of the small size of the specimens, accurate machining which will

not introduce any extraneous stress or bending is critical There are various

means of machining the specimens, depending on the form of the product

available Disks can be extracted from a plate by stamping or by turning

down a small diameter rod and subsequently slicing disks from the rod

Vari-ous methods of cutting, from coarse saw blades and fine-blade cut-off wheels

to electrical discharge machining (EDM), can be used to slice the disks

In previous studies [/], specimens were prepared using ingot and rapidly

solidified materials The material chosen to test the validity of the MDBT

concept was 316 stainless steel (SS) with 20% cold-works (CW) obtained in

0.348-mm-thick rolled sheet.^ The specimens were stamped to a diameter of

3.000 + 0.0076 mm and were subsequently precision lapped to a thickness of

0.2540 ± 0.0025 mm Precision machine lapping was performed to ensure

•'Material obtained from Hantord Engineering Development Laboratory (HEDL), heat

desig-nation 87210, otherwise known in the breeder reactor development program as HEDL N-LOT

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that the desired specimen thickness was achieved uniformly across the

diame-ter of the specimen

Rapidly solidified materials were provided in rod form [5] The rods were

cut in half and one rod for each alloy was cold swaged to obtain a 20%

reduc-tion in area The six rods were then turned down to a diameter of 3.000 ±

0.0127 mm Specimens of 0.381 mm thickness were cut using a high speed,

water-cooled, silicon carbide blade and were subsequently precision lapped to

0.2540 ± 0.0025 mm thickness These alloys were chosen for irradiation

test-ing

All cutting methods produce a layer of disturbed metal on the surface of the

machined part In the case of miniature disks, this layer can be a large

per-centage of the material involved, and the mechanical response can be

signifi-cantly altered by the presence of this disturbed layer

A study [6] has been conducted to determine the extent of the disturbed

layer produced by various cutting processes Other studies [7,8] which

con-firm the findings reported in Ref 6 have been conducted A standard

fine-blade cut-off wheel can produce as much as a 0.6-mm-thick layer of damage

near the surface Precision lapping is the recommended procedure to

elimi-nate this layer; however, this can be a slow and costly process when a great

deal of material must be lapped off or when the specimens in the lap batch are

of widely differing thicknesses

Recently, the alternative method of traveling wire EDM cutting has been

investigated Traveling wire EDM [8] is an extremely accurate cutting

pro-cess The recast layer is typically on the order of 0.005 to 0.008 mm thick [8],

depending on the material and cutting conditions, which is much less than

the 0.6 mm of disturbed metal produced by a cut-off wheel Since these layers

of disturbed metal caused by EDM are small and the cut edges are very flat

and parallel, a shorter and therefore less expensive lapping procedure is

re-quired The EDM/lapping technique was implemented to demonstrate its

su-periority over other methods In addition to the recast layer created during

the EDM cutting, there is also a heat-affected zone (HAZ) adjacent to the

recast layer The HAZ thickness is approximately the same as the recast layer

for steels Both layers must be removed by lapping

A 152.4-mm-long, 12.7-mm-diameter rod was turned down using a piece

cut from a 127-mm-thick plate of 304L stainless steel This rod was then

sliced by traveling wire EDM to produce 1.9558 ± 0.00254 mm thick disks

They were then precision lapped to 1.8872 ± 0.00254 mm A thickness of

0.0686 mm was lapped off and a substantial time saving was realized because

all the disks had nearly the same thickness and were already very flat

The EDM process results in a cratered surface (Fig 4) Figure 5 shows the

recast layer using scanning electron microscopy (SEM) Micrographs taken

after lapping showed that the lapping procedure is quite effective in removing

the recast and HAZ layers and in producing the desired specimen dimensions

with sufficient accuracy

Another useful method for proving that the disturbed metal was eliminated

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::oc:

FIG 4—A light micrograph showing EDM cratered cut surface profile

is to measure the microhardness of the various layers A disk was sectioned,

mounted, and polished, and microhardness measurements were taken at

var-ious distances from the EDM cut edge The result is shown in Fig 6 A lapped

disk was then tested in a similar fashion Microhardness readings

representa-tive of the parent metal region were obtained for the near surface of the

lapped specimen This further verifies the successful minimization of the

dis-turbed layers by lapping

Although Knoop microhardness measurements can be performed in

inter-vals of as little as 0.0254 mm, hardening due to plastic flow does occur in the

immediate surrounding regions and will affect the results Therefore, to

at-tain the results in Fig 6, microhardness measurements were taken at 0.0127

mm intervals or greater (depending on the material and indenter load) from

the specimen edge through the thickness, while staggering the location

paral-lel to the cut edge

Specimen and Test Parameter Variations

Experiments were performed to assess the ability of the MDBT to resolve

strain rate effects In general, important strain rate dependence is observed

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FIG S—Scanning electron micrograph showing an EDM cut surface

only at high temperatures and low strain rates For 316 SS, Paxton [9]

re-ported negligible strain rate dependence for strain rates in excess of about

10"-' s~' at 650°C This behavior is shown in Fig 7 for this material for

Curves 1 to 4 at 500°C The ability of the MDBT to clearly resolve strain rate

effects, when they are present, is demonstrated by comparison of Curves 5

and 6 at 650°C with Curves 1 to 4 at 500°C

For uniaxial tensile testing, the strain rate is clearly defined and is directly

proportional to extension velocity In the MDBT, however, the nonuniform

biaxial stress field makes it impossible to obtain a simple analytical formula

relating velocity to local instantaneous strain rate Also, the instantaneous

strain rate varies throughout the plate as the deformation proceeds

In the MDBT experiments, an approximate definition of average strain

rate was adopted:

(Aejv

(1)

where

€ = average MDBT strain rate,

Af„ = time to reach maximum central load

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Measurements Taken on Top

of a Lapped Disk Fell Within This Range

E D M C u t After Lapping — Measurements Taken Through Specimen Thickness

1 1 1 1

100

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Depth Into Surface, mm

FIG 6—Knoop microhardness as a function of depth measured from specimen outer edge

V = punch velocity,

w„ = central deflection at maximum load, and

Ae„ = equivalent biaxial strain under the hemispherical punch at the load

maximum

The average strain rates reported in Fig 7 for the 20% CW 316 SS were

ob-tained by this procedure

Another parameter of interest is the aspect ratio (AR) of the specimens,

defined as the diameter-to-thickness ratio This was varied by changing the

thickness and holding the diameter and all other experimental variables

con-stant

Large-AR-variation tests were performed to assess the range of AR's that

could be tested using the MDBT procedure For data inversion purposes, it is

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C e n t r a 0.030

Maximum Load

3

D e f l e c t i o n ( i n ) 0.04O 0.050 0.060 0.070

1 1 1 1 1 1 I 1

500 °C

1 — f = 6.0 X 10-< s e c ' Velocity = 4.23 x 10-3 mm/sec (0.010 inymin) -

2 — « = 6.0 X 10-3 »ec-1 Velocity ' 4.23 x 1 0 - ^ mm/sec (0.100 ln./mln)

3 — ! =• 6.0 X 10-3 «ec-1 Velocity = 4.23 x 10-2 mm/sec (0.100 inVmin)

4 — f = 3.0 X 10-2 5ec-1 Velocity = 2.12 X 1 0 - ' mm/«ec (0.500 in./mln) /•• 2

/ ^ 4

X.^—6

650 °C

5 — f = 4.0 X 10-5 sec-1 Velocity » 1.91 X 10-4 mm/sec (0.00045 inymin)

6 — ? = 1.0 X 10-2 , e c - 1 Velocity = 4.66 x 10-2 mm/sec (0.110 in./mln)

r 1 1 1 1

u

60.0 -O

Central Deflection (mm)

FIG 7—Demonstration of miniaturized disk bend test ability to resolve strain rate effects

preferable to standardize the specimen dimensions so that a large finite

ele-ment data base can be developed However, it is possible that some material

processing conditions or irradiation space limitations may necessitate a

change in specimen size

Figure 8 presents the results for 302 SS specimens with AR's varying from

11.8 to 118.0 A plastic wrinkling instability was discovered for an AR of

118.0 as evidenced by the rapid load drop for Curve 1 in Fig 8 Figure 9

shows the radial wrinkle that developed at the point of instability Another

specimen with an AR of 118.0 was loaded to a level short of the buckling load

as shown in Curve 7 of Fig 8 There was a permanent deformation in the

specimen but no radial wrinkle present Further evidence that the observed

phenomenon is a plastic instability was obtained by testing a specimen with

an AR of 59.0 at 500°C No instability phenomena were observed Therefore

it was concluded that the MDBT procedure is reliable and applicable for

specimens with AR's of less than about 60.0

The variation of specimen thickness was investigated to assess exactly what

machining tolerances result in acceptably small effects on the experimental

data The specimens used were 316 SS with a 3.0 mm diameter and were

precision lapped to a thickness of 0.254 mm These specimens were

subse-quently hand lapped on one side to provide for small thickness variations

The specimens were tested with the hand lapped side facing the punch It was

discovered that thickness variations of ±0.0051 mm produce central load/

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Centrel Deflection (mm)

1.4 1.6 1.8

FIG 8—Large aspect ratio parametric investigation

Radial Wave

FIG 9—(left)f/astic wrinkling instability resulting in a radial wave for 302 SS specimen with

aspect ratio of 118.0 tested at room temperature, (right) Axisymmetric deformation for 302 SS

specimen with aspect ratio of 59.0 tested at room temperature

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deflection data that are within the extremes of the reproducibility band for

specimens of nominal thickness Using the precision lapping technique,

tol-erances of ±0.0013 mm and better are readily achievable for large batches

of specimens It is recommended that the level of machining accuracy be

~ ±0.0013 mm, although variations of ±0.0051 mm will still provide useful

results when greater machining accuracy is not attained

Specimen Identification

Since the MDBT was originally developed primarily for post-irradiation

applications, it was imperative to find a method of identifying specimens

without altering their mechanical response A second criterion was that the

identification characteristic must be visible on remote closed-circuit television

cameras for hot cell sorting of the samples Three methods of identification

have been investigated: radial slitting, stylus engraving, and laser engraving

Radial slits 0.254 mm wide were cut through the thickness on the outer

specimen edge approximately 0.254 mm apart The radial depths of the slits

for a given specimen were 0.254 or 0.127 mm Because the removal of

mate-rial from the outer edge significantly decreases plate stiffness, this method of

identification was found to be unacceptable

Another method of specimen identification that was examined is to engrave

alphanumeric characters on one or both specimen surfaces These

identifica-tion processes can be quantified by measuring the height of the lip from the

specimen surface, the width of the track at the specimen surface, and the

depth of the track below the specimen surface Table 1 lists measurements of

these parameters made using an optical depth micrometer for three specimen

groups which were prepared from 316 SS with 20% CW The Group 1

speci-mens were engraved by hand and the tracks were relatively shallow and

nar-row Tests were performed at room temperature using specimens with one

and two sides engraved, and the central load/deflection curves were found to

be within the reproducibility band for this material

TABLE 1 — Characteristics of engraving tracks on specimens

2 Stylus Engraved 0.0127 to 0.02032 0.127 to 0.254 0.0127 to 0.03302

3 Laser Engraved 0.03048 to 0.04572 0.02032 to 0.02794 0.00254 to 0.00508

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The Group 2 specimens were stylus engraved; the tracks were on one side

only and were relatively wide and deep The central load/deflection curves for

the engraved samples were found to be quite different from the unengraved

samples at room temperature and at 500°C The Group 3 specimens were

laser engraved on one side The central load/deflection curves for the Group 3

samples were found to be within the reproducibility band of the unengraved

samples for tests conducted at room temperature and at 500°C

In summary, stylus engraving is acceptable, provided that the character

tracks are relatively narrow and shallow; wide and deep tracks reduce plate

stiffness However, one-sided laser engraving is preferable because the

exfoli-ated lip height is greater than the lip obtained by shallow stylus tracks and is

more visible for hot cell sorting after irradiation

Experimental Techniques

The central load and central deflections for 316 SS specimens were found to

be in the range of 0 to 650 N and 0 to 1 mm, respectively Therefore special

care must be exercised in designing the apparatus and in measuring load,

displacement, and temperature to ensure that accurate and reproducible

data are obtained

Apparatus Design

The test apparatus developed at MIT was adapted to an Instron 1331

servo-hydraulic machine with an environmental chamber and induction furnace

During the test, the applied load of the punch versus punch displacement is

measured Deflections are measured outside the environmental chamber with

two axial extensometers Incorporated in the load train is a water-cooled load

cell fabricated using semiconductor strain gages to provide accurate load

measurement Further design details for the load cell are presented in Ref 1

Some interfaces in the load train are pre-stressed to minimize nonlinear

contact responses High density alumina was chosen for the punch and die

material because of the large compressive strength, good wear resistance, and

above all, the low thermal conductivity of this material compared with the

steel specimens If the thermal conductivity is too high, accurate specimen

temperature control is difficult Aluminum oxide is a good thermal insulator,

particularly at high temperatures For room temperature testing, tool steel is

a good choice because the compressive strength is usually adequate, the wear

resistance is reasonable, and the thermal conductivity is not of concern Also,

tool steel is easier to machine than alumina and therefore less expensive

Ce-ramics are, of course, brittle, requiring care in punch tip design However,

the compressive strength of high density alumina is sufficient to carry the

loads present in the MDBT for hemispherical punch tip radii in excess of

0.254 mm, and the experiments verified this fact

Tiêu đề	The Use of Small-Scale Specimens for Testing Irradiated Material
Tác giả	W. R. Corwin, G. E. Lucas
Trường học	University of California Santa Barbara
Chuyên ngành	Nuclear Technology and Applications
Thể loại	Special Technical Publication
Năm xuất bản	1986
Thành phố	Baltimore

Định dạng
Số trang	387
Dung lượng	6,35 MB