IHSE

Institute for Materials Science and Engineering

FRACTUREAND

DEFORMATION

NAS-NRC

Assessment Panel

February 2-3, 1 989

NISTIR 88-3841

U.S. Department of Commerce

National Institute of Standards

and Technology

QC— W

100

U56

88-3841

1988

C.2

Selector

Technical Activities

1988

o
For a unidirectional graphite-fiberreinforced epoxy-matrix composite,

the direction of stress wave propagation is influenced by small

changes in elastic properties

caused by saturation (WET) of the

epoxy matrix from a dehydrated

(DRY) state. Only the quasitransverse (QT) wave is affected by

small changes in elastic properties. The unaffected quasilongitudinal (QL) wave propagates aiong a

preferred path of fiber orientation,

which is shown in the cutaway

view. The array of transducers

along with appropriate circuitry

(selector) is used to display an

insitu shift in the received stress

wave.

Reported by: 1. R.D. Kriz, “Monitoring Elastic Stiffness Degradation in

Graphite/Epoxy Composites," in

Solid Mechanics Research for

Quantitative Non-Destructive Evaluation, Dortrecht, The Netherlands:

Martinus Nighoff, 1987, pp. 389-

395. 2. Patent No. 4,499,770, Feb.

19, 1985. 3. D.W. Fitting, R.D. Kriz,

and A.V. Clark, “Measuring In- plane Elastic Moduli of Composites with Arrays of Phase-Insensitive Ultrasound Receivers,” in Review of Progress in Quantitative

NDE, New York: Plenum in press.
Institute for Materials Science and Engineering

FRACTUREAND

DEFORMATION

H.l. McHenry, Chief

NAS-NRC

Assessment Panel

February 2-3, 1989

NISTIR 88-3841

U.S. Department of Commerce

National Institute of Standards and Technology

October 1988

Technical Activities?

1988

dF'sf .rfi' <s#'

v*

CONTENTS

DIVISION ORGANIZATION iv

INTRODUCTION 1

RESEARCH STAFF 5

TECHNICAL ACTIVITIES 9

Performance 11

Fracture Mechanics 11

Fracture Physics 17

Nondestructive Evaluation 21

Composites 31

Properties 39

Cryogenic Materials 39

Physical Properties 48

Processing 55

Welding 55

Thermomechanical Processing 59

OUTPUTS AND INTERACTIONS 65

Selected Recent Publications 67

Selected Technical and Professional Committee Leadership 74

Awards 76

Industrial and Academic Interactions 77

APPENDIX 83

Fracture and Deformation Division 85

Institute for Materials Science and Engineering 86

National Institute of Standards and Technology 87

iii
DIVISION ORGANIZATION

Harry I. McHenry, Chief

( 303 )

PERFORMANCE

Fracture Mechanics

Fracture Physics

Nondestructive Evaluation

Composites

PROPERTIES

Cryogenic Materials

Physical Properties

PROCESSING

Welding

Thermomechanical Processing

ADMINISTRATIVE SUPPORT

Administrative Officer

Division Secretary

Group Secretaries

497-3268

David T. Read

( 303 ) 497-3853

Ing-Hour Lin

( 303 ) 497-5791

Alfred V. Clark, Jr.

( 303 ) 497-3159

Ronald D. Kriz

( 303 ) 497-3547

Richard P . Reed

( 303 ) 497-3870

Hassel M. Ledbetter

( 303 ) 497-3443

Thomas A. Siewert

( 303 ) 497-3523

Yi-Wen Cheng

( 303 ) 497-5545

Kathy S. Sherlock

( 303 ) 497-3288

Heidi M. Quartemont

( 303 ) 497-3251

Vonnie J . Edgins

( 303 ) 497-5338

Chris J . King

( 303 ) 497-5350

iv
INTRODUCTION

FRACTURE AND DEFORMATION DIVISION

Harry I . McHenry

Chief

The research of the Fracture and Deformation Division is directed

toward improving the structural safety and fostering the use of

advanced materials. Research on fracture mechanics, nondestructive evaluation, and welding technology contributes to the safe

and efficient performance of materials in structural applications. The development of better deformation-processing methods

and quality-control sensors improves the processing and properties of advanced materials. Deformation and fracture studies

based on solid-state physics and dislocation mechanics provide

a basic understanding of the structure and physical properties

of advanced materials and the role of imperfections.

Our interdisciplinary staff is organized into specific research

groups in the general areas of materials performance, properties,

and processing. Each group is headed by a recognized expert in

that technology who provides a focal point for industrial cooperations, scientific interactions, and technology transfer.

Historically, the division has emphasized materials research to

improve structural safety, but now we are directing more of our

efforts toward the National Institute of Standards and Technology

goal of increased industrial competitiveness. In support of the

long-range plan of the Institute of Materials Science and Engineering, our new programs focus on advanced materials with high

commercial potential and emphasize research on materials processing, which is the key to improved productivity in the metals

industry. We also conduct materials research for other government agencies and provide technical services to industries, universities, and other scientific laboratories.

3
Improving structural safety and fostering the use of advanced

materials is essential to increase the competitiveness of American industry. Fracture and its prevention cost the U.S. economy

4 percent of our GNP ($116 billion in 1981, the year of the NBS—

Battelle study for Congress) ; industry can save about 50 percent

of these costs by technological means. The market for advanced

materials is projected to reach $80 billion by the year 2000, and

the value of new products made from these materials is substantially greater.

American industry leads the world in the development of advanced

materials, but frequently we trail in using these materials for

commercial products. The commercial lag is due to lack of confidence in the service performance of advanced materials, particularly safety and reliability. The Fracture and Deformation

Division programs are developing measurement methods, sensors,

standards, and reference data that will be used to measure the

quality of advanced materials and to assess their service performance. Once measurement methods and standards are developed,

industry can confidently use advanced materials to design and

manufacture new products.

4
RESEARCH STAFF

Austin, Mark W. Elastic properties

X-ray diffraction

Berger, J. R. Fracture mechanics

Photo mechanics

Dynamic fracture

Cheng, Yi-Wen Fatigue of metals

Fracture behavior of surface flaws

Fatigue- life predictions

Thermomechanical processing of steels

Clark, Alfred V. , Jr. Theoretical and experimental ultrasonics

Engineering mechanics

Nondestructive evaluation

Delgado, Luz M. Mechanical testing

Compilation of low- temperature reference data

Fitting, Dale W. Sensor arrays for NDE

Ultrasonic and radiographic NDE

Signal and image processing

NDE of composites

Heyliger, Paul R. Computational mechanics

Finite -element methods

Mechanics of composite materials

Kim, Sudook Elastic properties

Low- temperature physical properties

Ultrasonics

Kriz, Ronald D. Finite -element analysis for composites

Mechanics of composite materials

NDE of composite materials

Ledbetter, Hassel M. Physical properties of solids

Theory and measurement of elastic constants

Physical properties of austenitic steels

Measurement and modeling of physical

properties of composite materials

Martensite- transformation theory

Lin, Ing-Hour Fracture- toughening mechanisms

Ductile-brittle transition

Elastic interactions of cracks and defects

Dynamic deformation and fracture

Dislocation theory

7
McCowan, Chris N. Welding metallurgy

Mechanical properties at low temperatures

Metallography and fractography

McHenry , Harry I

Fracture mechanics

Low- temperature materials

Fracture control

Purtscher, Pat T. Fracture properties of high-strength steels

Metallography and fractography

Properties of materials at low temperatures

Read, David T. Physics of deformation and fracture

Elastic—plastic fracture mechanics

Mechanical properties of metals

Reed, Richard P. Mechanical properties

Low- temperature materials

Martensitic transformations

Schramm, Raymond E. Ultrasonic NDE of welds

Ultrasonic measurement of residual stress

Design of EMATs

Shepherd, Dominique Failure analysis

Metallography

Fractography

Shull, Peter J. Capacitive -array and eddy-current sensors

Electronics for EMATs

Nondestructive evaluation

Siewert, Thomas A. Welding metallurgy of steel

Gas-metal interactions during welding

Welding database management

Simon, Nancy J. Material properties at low temperatures

Database management of material properties

Handbook of material properties

Tobler, Ralph L. Fracture mechanics

Material properties at low temperatures

Low- temperature test standards

Walsh, Robert P. Mechanical properties at low temperatures

Mechanical test equipment

Yukawa , SFracture mechanics

Codes amd standards

Structural safety

8
TECHNICAL ACTIVITIES
* . f > ' 3
PERFORMANCE

The Fracture Mechanics, Fracture Physics, Nondestructive Evaluation, and

Composite Materials Groups work together to detect damage in metals and

composite materials and to assess the significance of the damage with

respect to service performance.

Fracture Mechanics

David T. Read

Research Leader

J. R. Berger, J. D. McColskey, H. I. McHenry, B. Petrovski.^

P. T. Purtscher, R. P. Reed, D. A. Shepherd, D. E. Widman,T S. Yukawa

Our research in fracture mechanics contributes to the development of

fracture-prevention standards for structural materials, especially steel

weldments. By using the concepts of elastic—plastic fracture mechanics, we

establish material- toughness requirements, allowable stress levels, minimum

service temperatures, and weld-quality standards. The quantitative methods

of fracture mechanics offer advantages over the empirical methods traditionally used to develop safety standards, particularly for advanced structures where prior experience is limited.

Representative accomplishments

® A new method, called the T-CTOD test, has been developed to locate

brittle zones in steel weldments.

* The crack-driving force due to residual stresses in repair-welded steel

plates has been measured using the NIST technique for direct measurement

of the J-contour integral.

Guest worker from the University of Belgrade, Belgrade, Yugoslavia.

tGraduate student, Colorado State University.

11
• Guidelines for the assessment of pressure-vessel safety were prepared

for the Occupational Safety and Health Administration. The guidelines

evolved from our earlier investigation of an oil -refinery disaster.

Local brittle zones

When we attempt to apply fracture mechanics to welded structures, material

toughness data are required for comparison with the crack-driving force.

Although residual stresses and material inhomogeneities cause difficulties

in the calculation of the crack- driving force, the major problem is obtaining reliable toughness values. Weld- toughness testing uses specimens with

precracks either in weld metal (WM) or in the heat-affected zone (HAZ)

Two factors cause scatter in the results: First, the test temperature is

usually in the ductile- to-brittle transition region, where scatter is high,

even in base metals, because fracture initiation is governed by weakestlink statistics. Second, the welding process can produce local brittle

zones (LBZ) , and when the precrack tip enters a brittle zone, low toughness

values result.

The HAZ is commonly reported to be the site of least toughness in a weldment. Recently, more detailed studies [Satoh and Toyoda (1986); Stout et

al . (1987)] of weldments for use in offshore structures have identified

various microstructures within the HAZ. A high probability of brittleness

was discovered for the coarse-grained HAZ microstructure.

The question of weld toughness has assumed practical importance in our

study of pressure -vessel repair welding. The issues regarding driving

force have been resolved to the extent that test results are sufficient

for engineering applications [publication 14]. Weldment toughness, however, remains unclear. We investigated a specimen design [fig. 1, adapted

from that of Kinzel (1948)] in which the crack tip samples weld metal,

HAZ, and base metal in a single specimen; its descriptive abbreviation

is T-CTOD, for transverse crack-tip opening displacement.

Weldments of four materials were tested using the T-CTOD specimen: 2^Cr—IMo

and IMn—Mo, pressure-vessel steels, a C—Mr. structural steel, and a highstrength, low-alloy (HSLA) steel. The results still had considerable scatter. A key problem is the nature of the statistical weakest- link behavior;

the probability of fracture depends on both the brittleness of the LBZ and

the amount of the precrack front occupied by the LBZ. In the T-CTOD specimen, the weld and base metals are well-sampled, but only a few millimeters

of HAZ are sampled. Thus, fracture values are scattered among values characteristic of the HAZ and values characteristic of other weld areas. A

practical testing problem is fatigue-crack curvature when the strengths of

the weld metal and base metal are significantly different.

Tests of T-CTOD specimens performed so far have indicated that weld metal

is the most brittle site in the HSLA steel; in the three other materials,

the most brittle site, apparently, is the HAZ. In the 2^Cr—IMo steel,

toughness tests indicated that the base metal adjacent to the metallographic HAZ, that is, the subcritical HAZ, is the most brittle site.

12
Fracture Plane

Base

Metal

Crack

Tip

Weld

Fatigue-Sharpened

Crack

Crack Tip

Figure 1. T-CTOD specimen.

Surface flaws

The calculation of the crack- driving force at a surface flaw for the

elastic-plastic case challenges fracture mechanics. Surface flaws are

complicated because the crack- front shape and the resulting stress—strain

fields cause three-dimensional effects. Approximations such as the line

spring model are used to predict the general behavior of the driving force

for shallow cracks in tension. The only accurate way to model the variability of the driving force along the crack front is finite-element

For cracks with this configuration, fracture initiates near the ends of

the cracks. In a cooperative program with GKSS, a German national laboratory, we obtained data on five specimens of a high-strength aluminum

alloy with surface cracks of various depths and aspect ratios. Because

of continuing advances in applications of finite-element analysis, five

reports of finite-element analyses of elastic—plastic surface cracks now

exist. Because the crack geometries in the finite-element analyses differed from those in the experiments, an interpolation—extrapolation scheme

was developed to relate the experimentally measured crack-mouth opening

displacement (CMOD) to the J- integral at the angle of maximum crack growth,

d*. This involved three factors: CTOD(0 - 0)/CMOD; J(9 = O)/CTOD(0 = 0),

and J(9*)/J(9 = 0) . Of these, J(9*)/J(9 =0) was the most uncertain, about

±20 percent.

analysis

13
We estimated J for the surface -cracked specimens, and from the fracture

surfaces, we measured the corresponding crack extension, Aa. Then we compared these (Aa,J) data, which are indicative of the apparent toughness of

specimen material, with values from standard testpieces. The surprising

result was that the apparent toughness values at the surface cracks were

2 to 3 times higher than those of the standard testpieces. The results

were the same for a second, high-strength aluminum alloy for which three

surface -crack data points were available. However, in a low- strength

alloy, the surface-crack data for two specimens matched the standard testpiece data.

The higher apparent toughness at surface cracks suggests the possibility of

increasing the efficiency of structural components whose critical flaws are

surface cracks.

Shallow-crack fracture mechanics

As a part of the International Research Project to Develop Shallow-Crack

Fracture Mechanics Tests, organized by the Edison Welding Institute, we

tested specially instrumented shallow-crack (a/W = 0.1) three-point-bend

fracture specimens. The crack-mouth opening displacement at the edge of

the specimens was found to be 15 percent greater than that at the center

This confirmed the finite-element analysis results of R. H. Dodds and

D. T. Read [publication 13].

Dynamic fracture analysis

In cooperation with the Department of Mechanical Engineering at the University of Maryland, stress- intensity factors for rapidly growing cracks are

being calculated from strain values measured along the crack path. The

procedures developed will be used to analyze data from wide plates tested

by NIST in Gaithersburg for the NRC-sponsored Wide-Plate Crack-Arrest

Program.

We have recently adjusted the orientation of the strain gages to 68° from

the crack path; at this angle, the static -strain term is zero. The running

crack produces a strain peak followed by a zero crossing after the crack

passes. Trial tests in hardened 4340 steel specimens were performed at the

University of Maryland. Plasticity effects in these specimens were eliminated to enable unambiguous comparison with calculated results, which are

based on linear-elastic fracture -mechanics theory. In the development of

the analysis procedure, research focuses on the need to assume constantvelocity crack propagation and the influence of higher order terms in the

crack-tip strain-field expansion. Comparisons will be made of the more

versatile and convenient strain-gage technique and the well-established

optical technique, which uses ultra-high-speed photography to record the

caustic at the tip of the running crack.

14
Stretch zones

This year our study of the nature of ductile fracture in austenitic steels

at cryogenic temperatures included an investigation of stretch zones.

These zones can be related to fracture toughness. At cryogenic temperatures, they are characteristic of crack tips in ductile ferritic steels and

aluminum, but they have not been observed in austenitic steels even though

these materials are ductile in every other sense. To investigate the difference in the materials and corresponding micromechanisms, the crack- tip

regions from a typical low-strength austenitic stainless steel and from a

ferritic steel with a stretch zone (tested in liquid nitrogen) were examined metallographically

The first crack growth in the austenitic steel was directly ahead of

the initial crack, into an area that was not significantly deformed (or

strained) prior to cracking, as shown in figure 2; therefore, no stretch

zone was observed in this region. Most of the strain was absorbed in wings

at 45° to the initial crack. In the ferritic steel, crack growth began

at about 45° to the initial crack. The more uniformly distributed strain

around the initial crack produced a blunted tip. After fracture, the

stretch zone was visible on the fracture surface.

Pressure-vessel safety

As a follow-up to our failure analysis of the pressure-vessel failure at

a Chicago refinery in 1984, we prepared "Guidelines for Pressure Vessel

Safety Assessment" for the Occupational Safety and Health Administration.

It is a technical report on the design, materials, fabrication, inspection,

current reliability, and damage experience for metallic pressure vessels

and tanks used in general-purpose industrial applications. These vessels

and tanks are usually designed and built to ASME Section VIII, Division 1 or API 620 code requirements, which are legal requirements in most places.

Alloys #1 & 2

High Strain Hardening

Austenitic Steels @ 76 K

Alloy #3

Low Strain Hardening

Ferritic Steel @ 233 K

Figure 2. Highly strained zones and initial crack growth.

15
Several other major failures have recently occurred in tanks and pressure

vessels. Inspections by vessel operators indicate that, in some environments, cracking is found in 30 to 50 percent of the vessels inspected. For

non-nuclear vessels, the ASME code specifies evaluation criteria for new

vessels only, not for inspection of in-service vessels. Many places have

standards for repair operations, but standards for in-service inspections

are rare. Vessel operators apparently are not attempting to establish such

standards

International standards for fracture mechanics

D. T. Read participated in a task group of the International Institute of

Welding (IIW) that has been working on an international standard for the

application of elastic—plastic fracture mechanics. The purpose of the

standard is to promote fracture -prevention measures, which are expensive,

but economically advantageous in the long run.

Groups from various countries have their own approaches, and the initial

attempt to adopt one of these as the international standard was not supported by delegates from other countries. The delegates thought that

fracture mechanics is developing too rapidly and that applications are too

varied for such an approach. Eventually, the group agreed on a different

strategy: rather than establishing a standard method for performing a

fracture -mechanics assessment, they established a standard method for

reporting the assessment. The proposed document

• presents an introduction to the basic principles of fracture

mechanics

• briefly describes all known current methods

• includes sample problems with solutions and comments

® requires that specific technical information be included in the

report to enable verification of its nature and quality

The IIW plans to advance this document, along with companion parts on different aspects of structural safety, to the International Standards Organization (ISO) as an international standard.

References

Kinzel, A. B. (1948). Ductility of steels for welded structures. Weld. J.

Res. Suppl. 27: 217s—234s.

Satoh, K. ; Toyoda, M. (1986). Guideline for fracture mechanics testing of

WM/HAZ. Document X-1113-86. Tokyo: International Institute of Welding.

Stout, R. D. et al. (1987). Weldability of Steels. New York: Welding

Research Council. 298—300.

16
Fracture Physics

V. Tewary,* R. M. Thomsont

Research of the Fracture Physics Group is directed toward understanding

(1) the fracture of materials in terms of their fundamental properties and

the interactions between cracks and dislocations and (2) the effects of external chemical environments on cracks in brittle materials. Many of our

studies model dislocation emission from sharp cracks and the influence of

dislocation shielding on material toughness.

Representative accomplishments

• A new model attributes cleavage initiation in steels to inclusions on

the cleavage plane, which suppress dislocation emission at the crack

tip

• Relativistic equations that govern crack shielding in dynamic fracture

were developed to explain why the plastic zone size decreases with crack

velocity at a given static stress - intensity factor.

Activation- energy calculations for dislocation emission from a crack

in silicon

Recent studies have indicated that previous estimates by J. Rice and

R. Thomson (RT) (1974) of the activation energy for emission of dislocations from crack tips are probably too high for many materials , and

also that nonblunting dislocation configurations are usually observed,

rather than dislocations that blunt the crack. In this study, we made

a series of calculations for silicon. One configuration was split into

• # # • Visiting scientist from Ohio State University, Columbus, Ohio,

t Institute Scientist, Institute for Materials Science and Engineering.

17
partial dislocations, whose stacking- fault energy value was determined

by P. Haasen (1983). The activation energy was, indeed, much less than

that in the original RT estimate. The lowest energy configuration,

obtained by using a two-dimensional estimate of the image term (similar

to that used in the RT estimate) is a blunting half- loop, but the threedimensional image contribution shifts the result toward lowering the energy

of the nonblunting configuration relative to the blunting case.

Effects of plate-like rigid inclusions on the ductile-brittle transition

We have proposed a simple model of dislocations, cracks, and inclusions

to study inclusion embrittlement in steels [publication 32]. The elastic

interactions among screw dislocations, a plate- like rigid inclusion, and a

crack under antiplane shear strain, as shown in figure 3, were derived and

applied to a study of dislocation emission at crack tips and crack-tip

breakaway from shielding dislocations. Our results suggest that the

stress - intensity factor required for emitting a dislocation at a crack tip

increases, and the intrinsic character of cracks changes from ductile to

brittle when a plate- like rigid inclusion is on the cleavage plane and very

close to the crack tip. Furthermore, the inclusion- induced cleavage fracture triggered by void nucleation at the inclusion was analyzed qualitatively to account for the fracture toughness in steel, which decreases with

an increase in the volume fraction of inclusions.

*2

Figure 3. Coordinate system for dislocation—crack—inclusion interactions.

The crack tip is at the origin with the cleavage plane along the

negative x x axis. The inclusion is along the positive x1 axis

with its tip at x x = w. The dislocation is at f , measured from

the crack tip.

18
Crack shielding in the context of a composite

During interlaminar failure of a brittle polymer -matrix composite in which

the crack lies parallel to the fiber direction, there is an elastic interaction between the fiber and the crack that can be analyzed by using previously developed ideas for crack shielding by dislocations. We have

developed an analysis along these lines, modeling the fibers as line forces and line-force multiples, which indicate the shielding and antishielding. We also investigated the branching forces on the crack due to the

fibers. Somewhat different concepts apply to ductile polymer-matrix composites, and in this case, we shall develop a shielding model based on the

Bilby—Cottrell—Swinden (BCS) theory.

Dynamic- fracture toughness

To develop the relativistic equations that govern crack shielding, we

took the one -dimensional BCS model [modified by S. J. Chang and S. M. Ohr

(1981)], which serves as a zeroth-order approximation for all dislocation

crack- shielding modeling, and generalized it to steady-state relativistic

velocities [publication 33]. This crack shielding is illustrated in figure 4. Later, we shall pursue the consequences of dislocation- free zones

and ligament shielding for fast fracture and arrest and compare such models

with the continuum-based case. Although some controversy exists about the

presence of dislocation- free zones and the role they play in fracture, we

think that they should not be ignored in modeling the crack- tip behavior.

In particular, we think that the fracture toughness laws for fast crack

growth and arrest should incorporate ideas about the dislocation- free zone

in order to ensure that the proper physics of the crack—dislocation interactions has been incorporated into the final models.

e

o

a « » e • » ^

Figure 4. Moving crack with self- similar shield and wake. For a moving

crack in the steady state, we assume that a self -similar shield

is generated at each position and the energy of moving this

shield is equivalent to creating a wake for each dislocation

in the shield.

19
The chemical wedge in brittle fracture

A new theory has been developed for the observed activated crack growth

that incorporates the discrete effects at the crack tip with the long-range

surface forces . When external chemical environments are present during

fracture, one of the issues that must be settled is whether the external

molecules reach the crack tip. If the external molecules do not reach the

tip, then any activated crack growth observed is due to molecular transport

through the near- tip region, rather than to stress-assisted chemical reactions. It turns out that the criterion for reaching the tip is complicated

in the case of molecules that are large compared with the crack- tip opening

at the relevant stress -intensity level. Suppose, for example, that the

molecules are large and that a region exists near the crack tip from which

they are excluded because of their size. Since the surface area covered by

the external molecules has a surface energy different from that just ahead

of the last molecule (wedge tip) , a surface tension operates on the wedge

tip that tends to draw the molecules further into the crack- tip region. As

this happens, the molecules push the walls of the crack open, thus generating compensating elastic-configuration forces on the molecular wedge. When

the surface tension force is equal and opposite to the elastic forces exerted by the walls, the wedge comes into a Griffith- type equilibrium. We

have carried out detailed atomic calculations based on lattice Green’s

functions for the case of water interacting with a crack in mica.

References

Chang, S. J; Ohr, S. M. (1981). Dislocation-free zone model of fracture.

J. Appl. Phys . 52: 7174.

Haasen, P. (1983). Electronic processes at dislocation cores and crack

tips. Latanision, R. M. ; Pickens, J. R. , eds . Proceedings of a NATO

Advanced Research Institute on Atomics of Fracture . New York: Plenum. 707.

Rice, J.; Thomson, R. (1974). Ductile versus brittle behaviour of

crystals. Philos. Mag. 29: 73.

20
Nondestructive Evaluation

Alfred V. Clark, Jr.

Group Leader

D. W. Fitting, D. V. Mitrakovid,* R. E. Schramm, P. J. Shull

Our Nondestructive Evaluation (NDE) group develops measurement methods and

sensors for evaluating the properties and the processing of materials. To

improve structural safety, we use electromagnetic acoustic transducers

(EMATs) to detect and size flaws and to measure residual stresses. For

advanced materials, we develop sensors to monitor elastic property degradation in polymeric composites, sintering of ceramics, curing of polymers,

and crystalline texture formation in steel sheet.

Representative accomplishments

• Acoustical arrays of piezoelectric polymer elements were developed to

measure elastic-wave propagation in composites.

• Capacitive array probes, which are sensitive to the change in dielectric

constant during material processing, successfully monitored the cure of

a polymer-matrix composite.

• A flaw detection system for railroad wheels was developed for use in a

roll-by mode. EMATs were mounted inside a cavity in a railroad track

and automatically pulsed when a railroad wheel was on top of it.

• Proof-of -concept experiments were conducted for a nondestructive, online formability sensor. Ultrasonic velocity measurements related to

crystalline texture correlated well with destructive measurements of

formability

Guest worker from the University of Belgrade, Belgrade, Yugoslavia.

21
Acoustical arrays

Acoustical arrays were constructed from a piezoelectric polymer and polyvinylidene fluoride. Because the array elements are smaller than the

acoustical wavelength used, the output of the array is less affected by

artifacts than the output of a conventional acoustical transducer, which

averages the signal over the entire transducer aperture. The output of the

acoustical arrays is broadband—200 kHz to 35 MHz. Measured electrical and

acoustical crosstalk (interference between adjacent array elements) is

small (about 1 part in 10 3 ). Because each array element is omnidirectional, the array can be steered; that is, by suitably delaying the output

of each array element, the array can be made more responsive to signals

arriving from a chosen direction.

A promising use for acoustical arrays is the characterization of composite

materials, such as graphite/epoxy panels. The basic concept is illustrated

in figure 5: a receiving array detects an ultrasonic wave propagating at

an angle to the graphite fiber direction. By measuring phase velocities

at different angles to the fiber directions and using the known relation

between the composite elastic moduli and phase velocities, the elastic

properties can be obtained.

RECEIVING

ARRAY

FIBERS

Figure 5. Basic concept of acoustical arrays.

Composite materials have a peculiarity not found in isotropic materials,

such as metals. Because composites are anisotropic, the direction of

energy- flux propagation will not usually coincide with the normal to surfaces of equal phase in the acoustical beam, as shown in figure 6. The

transmitting transducer, T, generates two beams, marked QL and QT (quasilongitudinal and quasi- transverse) ; each beam propagates its energy as

22
shown by the arrows. The surfaces of equal phase are normal to the wave

vector. In the QL beam, the particle motion is predominantly perpendicular

to the specimen surface; in the QT beam, the particle motion is predominantly tangential. In contrast, in an isotropic material, only one beam

propagates; it propagates along the wave-vector direction with particle

motion perpendicular to the surface.

WAVE VECTOR

Figure 6. Measurement of energy- flux direction and arrival time

in sectioned samples of a unidirectional composite.

Thus, to determine the elastic properties in a composite material, it is

necessary to

a. scan the array elements to determine where the QL and QT

beams arrive

b. record the arrival time of these beams

c. divide the times by specimen thickness to obtain an

equivalent velocity for each beam

d. perform an inversion to obtain elastic properties from

arrival times

To validate the above procedures, proof -of -concept experiments were performed. Specimens of a unidirectional graphite/epoxy panel were cut at

different angles to the fiber direction. In the experiments, the arrays

were fixed in place and scanning was done by multiplexing the array (addressing each element in sequence)

From the known elastic properties of the constituents (graphite and epoxy)

and the computed centroids of the measured beams, the energy- flux deviation

was calculated for each specimen. Flux deviation was measured for the QL

and QT beams and compared with the calculated predictions. Typical results

for the QL wave summarized in Table 1 show that good overall agreement was

obtained.

23
Table 1. Comparison of Energy-Flux Directions of QL Waves

Fiber

Angle

Bulk Wave

Predicted

Scanned

Receiver

Array Centroid of

Measured Amplitude

28 26.4 24.1 26.4

28 26.4 24.1 26.0

45 42.1 42.0 40.4

45 42.1 43.3 44.2

55 50.7 50.8 50.1

70 60.8 57.6 57.4

NOTE: All entries are in degrees.

Capacitive array probes

Work on the use of capacitive array probes for materials characterization

continues [publication 63]. Current research focuses on two applications:

monitoring the sintering of ceramics and monitoring the cure state of polymeric composites. In both cases, the dielectric constant of the material

changes during processing. The capacitive probe is sensitive to the dielectric constant of material in the vicinity of the probe, so the probe

should be a good process monitor.

The principle of probe operation is illustrated in figure 7a. A voltage is

placed across two electrodes, and the resulting electric field between the

electrodes is as shown. The field is most intense close to the electrodes

and decays with distance. The field can be modified by changing the electrode configuration, as shown in figure 7b. Here, two electrodes are at a

high potential ("source" electrodes) and two are at a lower potential

("receiver" electrodes). The resulting electric field is more intense

between the electrodes and spreads farther from the electrodes.

Source Receiver Source Receiver

y 4=4

\ 'E: Field /

1-Finger

""" /

Scaling

2-Finger

Scaling

(a) (b)

Figure 7. Principle of probe operation.

24
Measurements of probe admittance can be made to characterize material in

proximity to the probe. The admittance is the ratio of current flowing in

the receiver electrodes divided by the potential difference. The admittance is affected by the material dielectric constant, e, and by the distance, d, to the specimen surface.

In our work on sintering of ceramics, we have constructed probes of different geometries and tested them on a variety of ceramics with different e

Our initial idea was to multiplex the electrodes to vary the probe's electrical geometry and to use an elementary theory to predict both e and d

from our admittance measurements. Initial measurements did not agree with

theoretical predictions. After numerous experiments using several probes

on materials with a range of e , we discovered that one artifact was caused

by (a) the way our instrument measures admittance and (b) parasitic coupling of electrical flux to ground points in the probe environment.

Having identified sources of experimental error, we were able to suppress

some artifacts. For example, a specimen was placed atop a ground plane,

which is an aluminum sheet. Current in the sheet was added back into the

impedance analyzer, along with the receiver current. The result is shown

in figure 8 along with theoretical results. Good overall agreement was

obtained.

Figure 8. Comparison of theoretical (broken line) and experimental

(solid line) liftoff response for the capacitive array.

25
Monitoring the cure of graphite/epoxy composites is based on changes in

conductivity, o, and dielectric constant, e, with cure state. In general,

the composite's conductivity dominates the dielectric effect for the frequencies used in our experiments (in contrast with the ceramics case, where

conductivity is negligible). Consequently, an initial concern was that

composite conductivity would blind the probe to changes in electrical

properties within the specimen.

Proof- of- concept experiments showed that the probe can indeed follow the

cure of a composite. A thin film of commercial, fast-setting epoxy was

placed atop a 6 -mm- thick unidirectional plate of cured graphite/epoxy. The

panel was, in turn, placed atop the capacitive array probe. The magnitude

and phase of the receiver-electrode current were measured as a function of

time. As seen from the results in figure 9, the probe was indeed sensitive

to the cure state.

o>

0) T5,

<D

(0

(0

Time (min

Figure 9. Magnitude and phase of the receiver-electrode current.

Measurements were repeated with variations in operating frequency and probe

spatial frequency. As the operating frequency was decreased from 100 kHz

to 1 kHz, the phase changed more with time. This is in qualitative agreement with theory, which predicts a greater sensitivity to conductivity at

lower operating frequencies. As the spatial frequency was decreased,

electromagnetic field penetration of the composite increased, and greater

sensitivity to curing was observed, again in qualitative agreement with

theoretical expectations.

26
Electromagnetic—Acoustic Transducers

A. Evaluation of defects in railroad wheels in a roll-by mode

Our nondestructive evaluation of railroad wheels moved forward with the

receipt of sections of rail and several wheel sets (two wheels mounted on

an axle) . We constructed a short "railroad" from the rails and mounted the

wheel set on the tracks; see figure 10. With the laboratory- size railroad,

we were able to develop a technique to detect and evaluate defects in the

wheels as they rolled over the track.

In previous work, electromagnetic—acoustic transducers (EMATs) were placed

directly on the wheel tread to interrogate artificial defects (saw cuts)

[publications 9, 58, 59]. In the laboratory railroad, an EMAT was mounted

in a small cavity that we had machined into the rail. The wheel set was

positioned so that one wheel was directly over the EMAT, and signals reflected from defects were compared with those of the EMAT placed directly

on the wheel. Because the efficiency of EMAT signal generation is very

sensitive to liftoff (distance from EMAT to tread) , we were concerned about

how well the EMAT would perform in the rail. Preliminary experiments indicated that, by backing the EMAT coils with a flexible substrate to minimize

liftoff, a good signal- to-noise ratio could be achieved with the EMAT in

the rail.

Figure 10. Laboratory- size railroad.

27
The above experiments were performed in a static mode, that is, with the

wheel positioned directly over the EMAT. Next, a simple trigger was constructed that caused the EMAT to be pulsed when the wheel was atop the

EMAT. Simple roll-by tests were then performed. The wheel was propelled

by hand over the EMAT; the trigger caused the EMAT to generate and receive

signals in the tread as it passed by. These signals (captured on a highspeed transient recorder) compared favorably with those observed in the

static mode.

The transmitting EMAT coil was redesigned so that it generates the same

signal amplitude, but requires a lower drive current; it is identical to

the wire -wound receiving unit. The new EMAT is more reliable, and the life

of the MOSFET output stage in the pulser has been increased. Also, should

it be necessary, the pulser 's repetition rate can be increased.

The parameters limiting train speed are: (a) pulse-repetition frequency,

(b) signal-processing time requirements, and (c) distance between wheels

on a railroad truck. The maximum roll-by speed appears to be about 40 km/h

(25 mph) , but it is subject to further testing and development.

B. Ultrasonic measurement of steel-sheet formability

Previous research has focused on ultrasonic measurement of texture and

formability in aluminum alloy sheet [publications 6—8] . During the past

year, the focus shifted to steel. In this effort, we are collaborating

with the Advanced Steel Processing and Products Research Center (ASPPRC)

at the Colorado School of Mines and interacting with researchers in the

automobile and steel industries.

A prototype ultrasonic system was developed and demonstrated to industrial

sponsors of the ASPPRC. Their response was favorable because

a. current methods of characterization of steel-sheet formability

are destructive;

b. these methods are time-consuming;

c. they cannot be implemented in applications such as a rolling

mill or press shop;

d. the NIST prototype system has the potential to overcome all

the above objections.

A block diagram of the ultrasonic system is shown in figure 11. The function generator delivers a high-frequency signal to a high-current pulser.

The pulser can deliver short-duration current pulses of up to 150 A into a

load that is tuned with the impedance -matching circuit. The transmitting

EMAT generates a wave that is guided by the plate and detected with the

receiving EMAT. The output of the receiving EMAT goes through a special

matching network and into a low-noise, high-gain amplifier. The amplified

output is in the form of a sine wave of finite duration. The digital-gate

and comparator circuit selects a zero crossing (a time when the voltage is

zero) in the wave and stops the counter at that point. The counter has

been running continuously since receiving a trigger signal coincident with

the firing of the current pulse.

28
Acoustic Wave Plate

Figure 11. The ultrasonic system

The system was used to measure combinations of arrival times of guided

waves traveling at different angles relative to the sheet rolling direction. These measurements were done on low-carbon steel sheet typically

used for automobile bodies. Destructive measurements of the average formability, r, of these sheets had been made by the supplier.

A comparison of r with <Tso> is shown in figure 12; here, <Tso> =

(1/4) [T(0°) + r(90°) + 2T(45°)], where T(9 ) is arrival time of the guided

wave traveling at angle 6 to sheet rolling direction. As can be seen from

figure 12, good agreement was obtained between ultrasonic and destructive

formability measurements for a relatively small data set. Measurements on

a larger set of sheets supplied by a major automobile manufacturer are

currently under way. These sheets are typical of those used in press -shop

operation.

29
Figure 12. Comparison of ultrasonic and destructive

formability measurements.

30
Composites

Ronald D. Kriz

Research Leader

M. W. Austin, J. R. Berger, P. R. Heyliger, J. D. McColskey, V. Tewary*

Our research in composites emphasizes (a) the mechanics of fracture and

(b) the mechanics of nondestructive evaluation of particulate and fiberreinforced structural laminates. Cur approach to these topics is both

analytical and experimental. Unlike conventional homogeneous isotropic

materials, fiber-reinforced composites can be designed for specific

applications by controlling their wide range of parameters, which include

fiber volume fraction, fiber orientation, interface properties, laminate

stacking sequence, and fiber-matrix elastic properties. We study how

these design parameters relate to the mechanical performance of selected

composites

Representative accomplishments

• The accuracy of strain measurements made with an optical strain

diffractometer has been increased by a factor of 50. A manual system

using one camera has been replaced by an automatic system using four

cameras. Thirty- seven times more area can be scanned in one -twelfth

the time.

• For the first time, the deformation topologies of stress waves propagating in graphite/epoxy materials have been calculated using finiteelement analysis (FEA) . Previously predicted columnar wave structures

and mode transitions in displacement fields have been substantiated with

FEA.

*Visiting scientist from Ohio State University, Columbus

Ohio .

31
Composite fracture mechanics

Fracture mechanics is not as well established for composites as it is for

homogeneous isotropic materials. Therefore, we have been developing new

analytical and experimental methods to understand the physical significance

of different kinds of damage in laminated composites (i.e., ply cracks, interface cracks, delaminations, edge stresses). For sponsors, we have measured the mechanical properties of new materials that are candidates for

specific applications.

A. Analytical methods for calculating singularities in laminates

As part of a long-term project, we are studying new methods to predict

three types of singularities (fig. 13) at bimaterial interfaces in

laminated structural composites.

(a) free edge

t Figure 13. Types of

(b) ply crack (c) delamination

singularities at anisotropic bimaterial interfaces.

We are using Stroh's method to evaluate the free-edge and ply-crack singularities. We intend to study the delamination singularity by a Green's

function method that has recently been developed in our division. For the

three types of singularities, the total boundary -value problem is solved

numerically: enriched finite elements are used to model the near-field

singularities, and the coefficients of these singular terms are calculated

by the conventional finite-element-displacement method.

B. New composite materials for thermal- isolation straps

Thermal isolation straps are used in satellites, where long-term containment of cryogens is required for sensor cooling. In an earlier program

[publication 21], we evaluated glass-fiber-reinforced epoxy (Gl/Ep) material for this application. Subsequently, it replaced aluminum- oxide

fiber-reinforced epoxy (Al 2 0 3 /Ep) because its properties were superior:

32
lower thermal conductivity and higher stiffness and fatigue life. Recently, we tested the mechanical and thermal performance of an improved

material (Al 2 0 3 / PEEK*) . Properties determined from mechanical tests for

tension, compression, and in-plane shear were similar to those of Al 2 0 3 /Ep,

but the thermal conductivity measured by L. Sparks and D. Rulet was substantially better than that of Al 2 0 3 /Ep (see fig. 14).

Figure 14. Al 2 0 3 /PEEK, Al 2 0 3 /epoxy, and neat PEEK

and perpendicular (90°) to the fibers.

parallel ( 0 °)

Although quasi-static mechanical tests showed no improvement of Al 2 0 3 /PEEK

over Al 2 0 3 /Ep, we think that improved fatigue life of the thermal isolation

straps is possible. Because of the high strain- to-failure properties of

the Al 2 0 3 fibers, Al 2 0 3 /Ep is particularly suitable for filament winding.

Unfortunately, the manufacturer encountered many processing problems in

filament winding the fatigue straps fabricated from Al 2 0 3 /PEEK. Hence,

fatigue tests have been indefinitely postponed pending further research.

We think further research is warranted because of the low thermal conductivity of the material.

*PolyEther—Ether—Ketone

tproperties of Solids Group, Center for Chemical Engineering, National

Institute of Standards and Technology.

33
C. Mechanical tests of graphite- fiber- reinforced PEEK

In an aerospace application, graphite-fiber-reinforced PEEK (Gr/PEEK) is

being considered as a lightweight material for the containment of liquefied gas fuels. Our division received a contract to measure its mechanical properties at cryogenic temperatures. Preliminary results indicate

adequate strength, stiffness, and bond strengths for the intended application. Here, Gr/PEEK is superior to A1 2 0 3 /PEEK because of its higher

specific strength and stiffness.

Mechanics of nondestructive evaluation for composites

Our nondestructive evaluation (NDE) studies concentrate on (a) measuring

and mapping the mechanical deformation near damage in a composite laminate

with optical diffraction techniques and (b) developing a numerical model to

predict the full- field deformation topologies of stress waves propagating

through an off-axis unidirectional graphite/epoxy composite. Both efforts

emphasize modeling the mechanics of deformation as it relates to damage in

a quasi-static state of deformation and as it relates to the dynamic deformation of a propagating stress wave. Both topics address mechanics of deformation together with a commonly used NDE technique.

A. Determination of strain fields in damaged composite panels

Because damage in composite structural laminates is heterogeneous, an

inhomogeneous distribution of strains corresponds to the growth of this

damage. To map the distribution of this heterogeneous strain field, the

NIST optical strain-measurement technique [Moulder et al. (1986)] has been

improved. With this technique, we shall study the initiation and growth of

impact damage in structural laminates with emphasis on the relationships

between the damaged strain regions and laminate structural performance.

Several improvements have been realized on the NIST optical strainmeasurement technique. Briefly, it uses the optical diffraction of a

coherent light source to measure localized strain over a portion (i.e.,

1-mm diameter) of a deformed Moire grid, which is attached to the surface

of a specimen while under load. Strain is calculated from changes measured

in the diffraction pattern, which correspond to in-plane deformation of the

Moire grid.

More accurate strain measurements were obtained by measuring small displacements of the four first-order diffraction dots. This is accomplished

by calculating the centroid of the intensity of each of the four (north,

south, east, west) diffraction dots. Each diffraction dot is resolved with

a CCD camera (512 x 488 pixels) ; standard image-processing hardware and

software for personal computers are used. A sample of diffraction dot

intensity is shown in figure 15, where the useful portion of a diffraction

dot is resolved over approximately 80-pixel diameter.

34
280

Figure 15. Intensity profile of first-order diffraction dot.

Each diffraction- dot centroid has been resolved within 1/1000 of the pixel

dimension, which translates into a strain accuracy of ±100 /ze . (The previous system accuracy was ±5000 pe . ) The resolution has also been improved

by automating the position control, which is used to scan the deformed

Moire grid, and the image -processing system from the sample -compiled program. The previous manual system mapped only a small area (21 X 21 pixels)

in three days. The automated system maps a larger area (128 x 128 pixels)

in six hours.

B. Stress-wave topologies in off-axis graphite/epoxy composites

The topological propagation of stress waves in off-axis unidirectional

fiber-reinforced composites were modeled with finite elements [publication

15]

Solutions for the large finite-element grids were obtained in reasonable times by using the large memory and vectorizable features of the NIST

mainframe computer. In a unidirectional graphite/epoxy plate, waves propagate off the fiber axis. Wave speeds and propagation directions were

predicted by finite-element analysis and compared with those predicted by

Christofel's equation (plane stress and plane strain were assumed). The

agreement was excellent. Most significant were the actual deformation

topologies of the quasi- transverse and quasi- longitudinal waves; the geometric distribution of these columnar wave structures are demonstrated in

the minimum principal stress plot of figure 16. The mode transition of

polarization displacement fields that was predicted at higher fiber-volume

fractions was confirmed.

35
Potential applications are numerous. With this method, we are currently

studying the interaction of waves with damage in laminated composites and

the design of NDE arrays that match predicted wave topologies.

Transducer

Transducer

Figure 16. Stress -wave propagation in unidirectional graphite/epoxy

45° off-axis.

36
C. Nondestructive tests of part icle- reinforced rocket fuel

Young's modulus and internal friction were measured for forty specimens of

solid rocket fuel with a resonance NDE technique. Previous pulse-echo NDE

techniques produced results with a wide scatter in localized areas. The

resonance technique tests the entire volume of this particle-reinforced

material, which decreases scatter of results. Because specimens were not

cut to resonance length, Young's modulus was calculated from En = n

7 E,

where E is measured and n = 1, 2, 3 Future tests will relate the

formation of microvoids to changes in internal friction measurements, which

will lead to a better understanding of the natural aging process of these

particle-reinforced composites. These microvoids initiate as interfacial

debonding around imbedded particles.

Reference

Moulder, J. C.; Read, D. T.; Cardenas-Garcia , J. F. (1986). A new videooptical method for whole -field strain measurements. Proceedings , 1986 SEM

Spring Conference on Experimental Mechanics . Bethel, Connecticut: Society

for Experimental Mechanics. 700—705.

37
-

'
PROPERTIES

The Cryogenic Materials and Physical Properties Groups investigate the

behavior of materials at low temperature and measure and model the physical

properties of advanced materials, including composites, ceramics, and the

new high-critical- temperature superconductors.

Cryogenic Materials

Richard P. Reed

Group Leader

L. M. Delgado, J. K. Han,* T. Daniels, H. Lee,* C. J. King,

L. Ma , t p. T. Purtscher, N. J. Simon, R. L. Tobler, R. P. Walsh

We study the mechanical, physical, and metallurgical properties of

materials in the temperature range 4 to 295 K. Goals of our research are

the characterization and development of metals, alloys, and composites; the

development of testing procedures and standards; and the collection and

evaluation of material properties data.

A major program in recent years has been the development of materials technology to design and build superconducting magnets for fusion- energy systems. Because of our expertise in and unique facilities for measuring

tensile, shear, creep, and fatigue properties, we provide testing services,

design and safety assessments, and consultation on material selection and

properties for a wide range of cryogenic projects.

Representative accomplishments

• The interstitial strengthening of austenitic stainless steels was

evaluated from room temperature to 4 K.

Guest worker from Korea Advanced Institute of Science and Technology,

Seoul, Korea.

t Guest worker from the Institute of Metals, Shenyang, China.

39
• Selected mechanical and physical properties of indium were determined

in the temperature range 4 to 295 K.

• Standards for tensile and fracture - toughness testing at 4 K were

developed in a United States—Japan cooperative program and submitted

to the American Society for Testing and Materials.

• The properties of copper and beryllium copper from over one thousand

documents were added to our data base on cryogenic materials.

Interstitial strengthening of austenitic steels

Structural alloys that can withstand the large magnetic forces of superconducting magnets are needed. Since structural failure in these applications would result in unacceptable loss, these alloys must also have

excellent fracture toughness. Many of the low- temperature applications,

such as those in magnetic- fusion- energy reactors and high-energy-physics

magnets, require materials with high elastic moduli and low thermal and

electrical conductivities. Austenitic steels have been selected almost

exclusively for these uses. Recently, the Japan Atomic Energy Research

Institute has urged the Japanese steel companies to develop even stronger

and tougher austenitic steels (1200-MPa yield strength and 200-MPa-m^

fracture toughness at 4 K) for future use for structural constraint in

large magnetic fields. Research in Japan to achieve these goals, coupled

with research at NIST and other U.S. laboratories, has led to additions of

nitrogen to achieve higher strengths at low temperatures for both Fe—Cr—Ni

and Fe—Mn—Cr austenitic steels.

Additions of carbon and nitrogen to Fe—Cr—Ni-base austenites strongly

increase the yield and other flow strengths at low temperatures [publication 48]. This is illustrated in figure 17 for temperatures of 4, 76,

and 295 K. Despite its smaller atomic size, nitrogen increases the yield

strength at 4 K more than carbon by a factor of 1.4. Both carbon and

nitrogen contribute equally to the strength at 295 K. At 295 K, nitrogen

also has a larger strain-misfit parameter than carbon. The modulus -misfit

parameter of the carbon-plus-nitrogen content ([C+N]) is negative at 295 K

and positive at 4 K; this transition implies increased covalent bonding at

low temperatures, primarily that of nitrogen. The strengthening increase

at low temperatures from C+N addition (~G/2.5, where G is shear modulus)

is of the same order as carbon in nickel at low temperatures.

The values of the strain-rate sensitivity parameter, m = dine /dina, were

low. This implies that the stress field of the obstacle was short range.

Correspondingly, the activation volumes, V* were very low, especially at

4 K, where they were measured within the range 2 to 5b 3

, where b is Burgers

vector. These low values imply very localized interaction volumes. When

the case of a uniform array of obstacles is considered, V* equals bid,

where 5. is the average length of activated moving dislocation segments and

d is the effective diameter of the obstacle. For 1 atomic percent [C] or

[N]the average spacing of interstitial obstacles is about 4b. The

distance from the center of an octahedral hole in an fee lattice to the

40
Figure 17. Low- temperature tensile-yield strengths for a series

of austenitic stainless steels with varying [C+N]

41
nearest solvent atom is b- 2 . If we consider that this distance represents

the effective interstitial diameter, bid equals 2

3/2 b

3

, which is very close

to the 4-K values.

The observed dependence of V on [C+N] (fig. 18) is reasonable. Higher

interstitial contents would effectively reduce i, creating more (and

closer) activation sites. The ratio of the change of V* from 0.5 atomic

percent [C+N] to 1.5 atomic percent [C+N] was about 1.7 and was quite consistent at each temperature. The expected variation of uniformly spaced

discrete obstacles of such concentrations is from i — 5.7 b to 3.5 b, a ratio

of 1.6—certainly very close for these estimates.

Figure 18. Operational activation volume (7*) versus [C+N]

for selected true stress levels.

The dependence of operational activation volume, V , on temperature and

individual strain- rate -change data is also shown in figure 18. The very

low values of V* imply strengthening from obstacles with strong, shortrange stress fields. Also, the flow- strength temperature -dependence

parameters suggest that Friedel statistics with a dominant strain

42
interaction best describe [C+N] strengthening in austenite at low temperatures. This description also fits best with the misfit parameters.

The strain misfit of [C+N] is larger than that of solute elements and

accounts, at least partially, for interstitial strengthening.

Indium: Mechanical and Physical Properties

Indium and indium alloys are used extensively in high-technology applications because their excellent wetting characteristics enable reliable

joining of glass, ceramics, or metals. Recent failures of indium solder

joints in space applications have led to our research on its low temperature properties [publication 51].

Indium is the softest metal that is stable in air. During rolling or other

forming operations at 295 K, indium softens as a result of deformationinduced recrystallization. The primary reason for the softness of indium

at 295 K (Tr ) is the proximity of its melting temperature ( Tm = 429 K;

Tr/Tm = 0.69). Although the crystal structure of indium is commonly called

face-centered tetragonal, its true space group is (I4/mmm) , A = 2;

thus, its structure is actually body-centered tetragonal. Nominal lattice

constants are a = 0.32512 nm, c = 0.49467 nm, c/a = 1.5215. This tetragonality of structure ensures that its physical properties, such as thermal

expansion and elastic constants, are anisotropic. Indium is diamagnetic

and becomes superconducting at about 3.4 K.

Selected mechanical and physical properties of indium were determined

in the temperature range 4 to 295 K. Tensile properties, creep, axial

fatigue, torsion, and torsion fatigue were measured to assess mechanical

performance. Elastic properties, thermal expansion, and electrical

resistivity were measured to understand the low- temperature structure.

Twinning was prevalent as a deformation mode at all temperatures. Most

tensile load—strain curves included some serrated yielding at ail temperatures. We associate the serrations with deformation twinning. Even when

metallography was used, care had to be taken to identify deformation twins.

A pair of identical rectangular specimens was polished and then deformed

in compression at 76 and 295 K. Figure 19 shows the combination of slip

traces and deformation twins are shown following compressive deformation

at 76 K. The twin traces are not the same as the slip traces.

Deformation twin planes had been identified as (10T) and 1T0) ; across other

{110} planes, the twin symmetry already existed in the face-centered tetragonal lattice. The twins observed typically had one linear side and one

curvilinear side. Presumably, the linear trace is stable and represents

the compositional plane (10T) or 1T0) . The curved interface had been

mobile, providing twin growth. Most twins appeared to nucleate at grain

boundaries. With one end originating from the grain boundary, twins terminated in the interior of the grain. The interior-grain-twin interface was

lenticular on one side.

43

In figure 20, the stress at which serrations were first observed in the

stress—strain curves is plotted vs. test temperature. The yield and ultimate strengths and the stress at which serrations ceased are also included.

Usually, twinning-associated serrations began close to the yield strength

and terminated slightly below the ultimate strength. However, there were

large specimen- to- specimen variations in these stresses, as evidenced by

the wide data bands. Stress averages reached maxima at temperatures

between 10 and 76 K, but the data spreads were too large to place much

credence in these maxima.

'(75 Cl

coc

0)ro

coto©L. CO

©

"toc

©

Figure 20. Stresses for onset and cessation of serrations in stress—strain

curves; the serrations are associated with deformation twinning.

45
At room temperature, indium recrystallized during deformation; after lowtemperature mechanical -property tests, indium recrystallized on warming

to room temperature. At room temperature, indium failed in shear; at low

temperatures, failure was usually by microvoid coalescence and dimpled rupture, followed by shear. In fatigue at low temperatures, microcracks were

observed. The microcracks may be associated with grain boundaries or precipitates. In general, indium displayed characteristics similar to those

of a soft face-centered metal.

United States—Japan program for the development of test standards

A United States—Japan cooperative program is developing tensile and fracture toughness testing standards for austenitic stainless steels (construction materials for superconducting machinery) at 4 K. Sponsors of the

program are the U.S. Department of Energy, Office of Fusion Energy, and the

Japan Atomic Energy Research Institute (JAERI) . The program includes personnel exchanges, interlaboratory testing, and individual or cooperative

research programs. Contributing organizations include NIST, three other

American laboratories, JAERI, and six other Japanese laboratories.

During this program, which started in 1986, cryogenic materials scientists

were interviewed at government, industrial, and academic institutions in

Japan. Workshops were held in Sendai (March 1986 and January 1987) , Reno

(October 1986) and Tokai-mura (August 1986 and May 1988) . The first and

second round- robin tensile and fracture tests of Fe—13Cr—22Mn and Fe—25Cr—

15Ni austenitic stainless steels were completed by June 1988 [publication

39]

The proposed standard 4-K tensile test procedure has been written and

revised five times [publication 77]. Five drafts of the proposed 4-K fracture test standard were also prepared [publication 78]

In addition, an

experimental matrix of eighty tests was executed at five laboratories to

answer questions about test procedures. Six joint research papers were

published [publications 39, 40, 41, 62, 75, 81]. The draft standards have

now been submitted to ASTM for review and approval as consensus standards.

Material properties handbook

The Materials Handbook for Fusion Energy Systems (MHFES) is being developed

to provide an authoritative common source of material properties for the

fusion energy community to use in concept evaluation, design, safety analysis, and performance prediction and verification of fusion energy systems.

This single source for properties is essential to ensure a common basis for

material selection and design of the various fusion systems currently under

study, in operation, or under construction.

We are continuing to work on handbook pages for the MHFES covering lowtemperature properties of structural alloys for the superconducting

magnets. Mechanical properties (including tensile properties, fracture

toughness, fatigue and creep) and physical properties (including thermal,

46
electrical, and mechanical properties) are included in the temperature

range from 0 to 300 K. Three nitrogen- strengthened austenitic stainless

steels that are the most promising near-term candidates for structural use

in superconducting magnets were chosen for initial coverage. Evaluation

and analysis of copper (CDA 101—107) has been recently completed.

References

Byrnes, M. L. G. ; Grujicic, M. ; Owen, W. S. (1987). Acta Metall. 35:

1853-1862.

Reed, R. P. ; Purtscher, P. T.; Yushchenko, K. A. (1986). Nickel and

nitrogen alloying effects on the strength and toughness of austenitic

stainless steels at 4 K. Reed, R. P. ; Clark, A. F. , eds. Advances in

Cryogenic Engineering — Materials

vol. 32. New York: Plenum. 43—50.

Sakamoto, T.; Nakagawa, Y. ; Yamauchi, I.; Zaizen, T. ; Nakajima, H.

Shimamoto, S. (1984). Nitrogen-containing 25Cr—13Ni stainless steel as a

cryogenic structural material. Clark, A. F. ; Reed, R. P. Advances in

Cryogenic Engineering — Materials

vol. 30. New York: Plenum. 137—144.

Takahashi, Y. ; Yoshida, K. ; Shimada, M. ; Tada, E. ; Miura, R. ; Shimamoto, S.

(1982). Mechanical evaluation of nitrogen- strengthened stainless steels at

4 K. Reed, R. P. ; Clark, A. F. , eds. Advances in Cryogenic Engineering —

Materials , vol. 28. New York: Plenum. 73—82.

Tobler, R. L. ; Reed, R. P. (1980). Materials Studies for Magnetic Fusion

Energy Applications at Low Temperatures — III. Nat. Bur. Stand. (U.S.)

15-48.

47
Physical Properties

M. W. Austin, S. A. Kim, M. Lei,* R. R. Raot

Our research on deformation emphasizes measurements and modeling of elastic

constants and related physical properties for metals, alloys, composites,

ceramics, and the new oxide superconductors. For many studies, the temperatures range between 295 and 4 K. The elastic constants, which relate

deformation to stress, sustain our interest because they relate to fundamental solid-state phenomena: interatomic potentials, equations of state,

and phonon spectra. Furthermore, thermodynamics links elastic constants

with specific heat, thermal expansivity, atomic volume, and the Debye

temperature

Representative accomplishments

• The individual alloying effects on the elastic constants were determined for Fe-Cr—Ni—Mn austenitic steels.

• The five anisotropic elastic constants of graphite fibers were deduced

by measuring the elastic constants of Gr/Al and Gr/Mg composites and

using our theoretical model inversely.

• The complete set of elastic constants, from 5 to 295 K, of Y—Ba—Cu—0,

Ho-Ba—Cu—0, and Eu-Ba—Cu—0 were determined by ultrasonic methods.

^Graduate student from the Institute of Metal Research, Shenyang, China,

t Guest worker from the Indian Institute of Technology, Madras, India.

48
Austenitic steels

We determined the effects of several alloying elements—chromium, nickel,

molybdenum—on the elastic constants of Fe—Cr-Ni alloys. All three increase the bulk modulus, B, and decrease the shear modulus, G. In most

alloys, these two properties show parallel behavior. In these complicated 3d-electron transition-metal alloys, the nonparallel B—G behavior

may result from changing the d-electron-s-electron balance. Probably,

the d-electrons determine the shear modulus, which depends mainly on

interatomic-bond angles, and both d-electrons and s-electrons determine

the bulk modulus, which depends only on interatomic-bond lengths. Applying a modified Ducastelle model to our measurements showed the relative

contributions of repulsive energy and band- structure energy to the elastic constants. For both 4 and 295 K, figure 21 shows the fractional

band- structure—energy contribution to the bulk modulus. We see a lower

contribution at low temperatures and a decrease with the addition of carbon and nitrogen, which increase the unit-cell volume.

Figure 21. Percentage contribution of band- structure energy to total bulk

modulus. Effect of alloying interstitial carbon and nitrogen

into Fe—Cr—Ni alloy.

49
Composites

We determined the complete five - component transverse - isotropic - symmetry

elastic-constant tensor for two graphite fibers: one with high strength

and low modulus and one with low strength and high modulus. We did this

in two steps. First, we measured ultrasonically the complete elastic constants of a metal matrix with embedded uniaxial graphite fibers [publication 10]. Second, we did an inverse -modeling calculation to extract

the fiber's elastic constants. This calculation requires three inputs:

composite elastic constants, matrix elastic constants, and fiber-matrix

phase geometry, principally the fiber volume fraction. We compared the

results with those expected for a random quasi- isotropic graphite aggregate

and for a hypothetical graphite fiber with perfectly aligned basal planes.

Figure 22 shows the composite's microstructure.

Figure 22. Optical photomicrograph of transverse section of graphitefiber-reinforced magnesium-matrix composite. The fibers,

7 /xm in diameter, occupy 70 volume percent of the composite.

Graphite possesses remarkable physical properties. For example, the

within-basal -plane Young's modulus equals 902 GPa, four times that of iron

(212 GPa), and 80 percent of that of diamond (1141 GPa). Also, graphite

exhibits strong physical -property anisotropy: the E1 /E3 Young' s -modulus

ratio equals 29.8. (Here, subscript 1 denotes any direction in the basal

plane, which is isotropic, and subscript 3 denotes the axis perpendicular

to the basal plane.)

The fiber's elastic constants provide a valuable material characterization:

information on basal -plane alignment. Also, they enter many practical

problems, such as internal strain (residual stress).

50
Superconductors

Using ultrasonic methods, we determined the complete set of elastic constants, from 5 to 295 K, of several high-Tc metal-oxide superconductors:

Y—Ba—Cu—0, Ho— Ba—Cu—0, Eu—Ba—Cu—0 [publications 23—25, 29—31]. Focusing

on the yttrium oxide, we studied six specimens prepared at four laboratories. The bulk modulus, corrected to the void- free state, ranged from 54

to 101 GPa. Poisson's ratio, 0.21 ±0.02, compares closely with that of

BaTi03 (0.223) and SrTi0 3 (0.236), suggesting similar interatomic bonding.

At Tc (near 91 K) , within measurement error (0.1 percent), the elastic

constants showed no discontinuity.

To compare various physical-property measurements, we focused on the Debye

temperature, 8 [publication 25]. For example, from the elastic constants

of Y—Ba—Cu—0, we found 8 = 423 K; from specific heat, 8 = 440 K; from thermal expansion, 8 = 370 K; from hardness, 8 = 677 K. This wide range in 8

is inconsistent with fundamental interrelationships among related physical

properties

We studied ultrasonic -wave velocities, both longitudinal and shear, in

Y 1 Ba2 Cu3 0 7

_ x between 5 and 295 K during both cooling and warming [publication 11]. Both waves, especially the longitudinal, showed thermal hysteresis. The results suggest a hysteretic phase change that occurs between

160 and 70 K during cooling and between 170 and 260 K during warming. This

phase-change hypothesis explains anomalies in several physical properties.

The phase change agrees with predictions of thermodynamic instability. We

confirmed the hysteresis in Ho—Ba—Cu—0, where it is smaller than in Y—Ba—

Cu—0, and in Eu—Ba—Cu—0, where it is larger. In a companion perovskite,

BaTi0 3 , we observed zero hysteresis. At Tc , 91 K, sound velocities showed

no measurable change in either magnitude or slope. This continuity disputes the current popular view that, contrary to thermodynamics, elastic

stiffness increases upon cooling through Tc into the superconducting state.

We believe that stiffening results from the usual thermal effects after

a phase transformation from a stiffer phase. Figure 23 shows the hysteresis in three elastic constants: G, shear modulus; B, bulk modulus, and u,

Poisson's ratio.

We studied the elastic constants from 4 to 295 K of another type of superconductor: the Chevrel-phase PbMo 6 S 8

. The elastic constants show strong

temperature anomalies and strong associated anomalies in attenuation.

Cooling to 4 K brings about significant internal changes not attributable

to a crystal- structure change.

51
USin

o\

cm

Vy O

H- - O

USinO

CM

CQ

H'—

CQ

Figure 23. For Y1 Ba 2 Cu3 0 7 _ x , temperature variation of shear modulus, G\

bulk modulus, B ; and Poisson's ratio, v. Note the large

thermal hysteresis, especially in longitudinal modes.

52
Studies related to nondestructive evaluation

Although our sound-velocity studies, experimental and theoretical, proceed

mainly toward determining solid-state physical properties, many studies

relate to nondestructive evaluation.

Our study of a composite with continuous, uniaxial graphite fibers (70 volume percent) in a magnesium matrix included measurement, modeling, and

inverse modeling to obtain the fiber's elastic constants. By ultrasonicvelocity methods, we measured the composite's complete orthotropic- symmetry

elastic-constant tensor—Cjj i- n Voigt contracted notation. Approximately,

the composite shows transverse- isotropic symmetry. For a model, we used a

wave -scattering method in the long -wave length limit. The model requires

two inputs: the two isotropic matrix elastic constants and the five anisotropic fiber elastic constants. We measured the first and guessed the

second on the basis of graphite- fiber elastic constants reported by others.

This guess gave good measurement—model agreement for only Cllf C22 » and

C33 . Especially, the shear moduli CX1 (i = 4, 5, 6) agreed poorly (a 20-

percent difference) . Using inverse modeling (calculation of fiber properties from measured matrix properties and measured composite properties) , we

estimated the anisotropic fiber elastic constants. For the fiber, we predict a Young's modulus anisotropy of 12 and a principal range of Poisson's

ratio from 0.03 to 0.37. We also showed the neutron- diffraction textures

for both the matrix and the fiber.

Using a scattered-plane -wave ensemble -average model developed for composite

materials, we calculated the effective elastic constants of cast iron. We

focused on the effect of graphite-particle aspect ratio on Young's modulus.

Between model and observation, we found good agreement. Oblate -spheroidal

graphite flakes lower the elastic stiffnesses much more than do spheres.

To obtain good model—measurement agreement, we must use graphite's lower

third- order-bound (Kroner -bound) elastic constants. Besides Young's modulus, we calculated the usual quasi- isotropic elastic constants: shear modulus, Poisson's ratio, and bulk modulus.

Other studies

This year, other physical-property studies included the following materials: amber, barium titanate, strontium titanate, glass—epoxy composites,

an alumina- fiber/(poly) ether-ether-ketone composite, and a silicon-carbideparticle/aluminum-matrix composite

On the analytical—theoretical side, we focused on the thermoelastic coefficient and its pressure derivative. Using a Mie—Gruneisen interatomic

potential, we derived a relationship for the thermoelastic coefficient

K = — ( 1/T) (dT/da ) , the temperature change caused by stress, and for the

thermoelastic-coefficient pressure derivative, (1/K) (8K/8P ) . The latter,

related to third-order and fourth-order elastic constants, relates simply

and approximately to the bulk-modulus temperature derivative, (1/B) (dB/dT)

Comparison with a solid-mechanics model shows agreement within approximately twenty percent.

53
* •

•

,

-

*

'
PROCESSING

The Welding and Thermomechanical Processing Groups investigate the nonequilibrium metallurgical changes that occur during processing, such as

solidification, recrystallization, phase transformation, and precipitation

strengthening. These changes affect the quality, microstructure, properties, and performance of metals.

Welding

Thomas A. Siewert

Group Leader

G. Adam,* C. N. McCowan, D. A. Shepherd, D. P. Vigliotti

Since structural failures often originate at flaws in welds, the study of

welding is integral to our structural safety research. Our goals are to

develop procedures that reduce the incidence of defects and to develop weld

metals with improved tolerance for defects. We use a computerized fully

adaptive gas-metal arc-welding system to produce weld flaws for evaluation

of nondestructive test methods and for the study of microstructure—toughness

relationships in both the weld and heat-affected zone. Now we are using

these same capabilities to develop automated process controls.

Representative accomplishments

• A database of 950 welds was used to develop an improved diagram for predicting the ferrite content of stainless steel welds as a function of

chemical composition.

• A prototype radiation- transfer standard has been developed for use as an

image-quality indicator for real-time radiology.

• A gas-shielded arc-welding procedure has been developed to produce standard reference materials with uniform gas contents for use in calibrating

residual gas analyzers.

*Guest worker from the Nuclear Research Centre — Negev, Beer- Sheva

Israel

55
Stainless steel

In a cooperative program with the Welding Research Council, a diagram was

developed that predicts the ferrite content of stainless steel welds with

more accuracy than previous prediction diagrams [publication 72]

The new

diagram shown in figure 24 was developed from a database of 950 welds, and

it extends predictability to 100 FN (ferrite number) . Certain ferrite

ranges have been associated with cracking; others have been related to poor

corrosion resistance. The improved accuracy of this diagram gives greater

assurance that a composition will have the desired ferrite content. The

diagram has been evaluated for accuracy as a function of alloy content using

the 950 -weld database from which it was developed. It has proven accurate

within 2 FN for manganese contents to 10 mass percent, Mo contents to 3 mass

percent, and nitrogen contents to 0.20 mass percent.

The Welding Research Council's Subcommittee on the Welding of Stainless

Steel and the International Institute of Welding are evaluating the diagram

with independent data. Upon successful completion of this evaluation, it

will be submitted as a new standard to the American Welding Society and the

American Society of Mechanical Engineers.

18

16

14

12

10

Figure 24. New ferrite-prediction diagram for stainless steel welds.

56
Real-Time Radiology

Responding to the needs identified in the 1987 Workshop on Standards for

Real-Time Radioscopy, we developed a questionnaire on real-time systems and

their usage in this country. After a presentation at the 1988 ASTM winter

committee meetings, committee members offered to complete the questionnaire.

Preliminary results were reported at the 1988 summer committee meeting and

at a topical conference of the American Society for Nondestructive Testing

(ASNT) [publication 67], The final report will guide the development of a

radiation transfer standard in fiscal year 1989.

Current image-quality indicators, which were designed for film radiography

must be repositioned for each exposure. Thus, with these indicators, we

cannot exploit the advantages of real-time systems: dynamic evaluation and

rotation of the specimen without repositioning the detection system. New

standards are being developed to evaluate systems in real time. Prototype

standards with one- and two-dimensional symmetry have been produced and are

being evaluated; their design concept is illustrated in figure 25.

Cross Section

y

Radiographic

Projection

-a -b b a

Figure 25. Real-time spheres.

57
Arc Physics

The arc -physics equipment in our welding laboratory continues to generate

cooperative programs. This spring, a graduate student helped to evaluate

voltage changes as a means of characterizing droplet transfer in gas -metal

arc welding [publication 34] . He found that voltage changes greater than

approximately 8 V correlated with short-circuiting transfer and voltage

changes between 1 and 4 V were associated with globular transfer. Intermediate voltage changes were associated with transitions between these

modes, and voltage changes of less than 1 V were associated with spray

transfer and electrical noise. These values are consistent with published

data and models for voltage drops across the arc. The results provide

another sensing methodology for intelligent closed- loop control of welding

processes

With the help of a guest worker, the data collection and processing capability is being upgraded. A digital oscilloscope with a 8-kilobyte memory

is being replaced by a 16 -MHz microcomputer with 1 -megabyte RAM and a

100-kHz A-to-D board. Its larger memory and improved processing capability

increase the resolution of transient behavior and the measurement of droplet

transfer rate. We shall use the new system to study an HY-80 gas-metal-arc

electrode; results will be compared with those of previous studies of a C—Mn

electrode

Gases in metals

The dissolution of shielding gases into the weld pool, which is usually considered a disadvantage in welding, is being turned into an advantage: This

technique is being used to develop standards for residual gas analyzers with

uniform gas levels, levels above those attainable by casting techniques. To

reduce specimen machining and variable penetration problems, the welds are

made in a grooved copper block. Since the weld metal does not wet the copper, the cylindrical weld bead can be removed. Preliminary evaluation of

nitrogen and oxygen in a C—Mn steel has demonstrated the feasibility of using the technique to produce standard reference materials. We are currently

evaluating specimens of hydrogen in titanium.

Analyses of fluxes

For many welding processes, the flux is an integral part of the electrode,

and it is evaluated during qualification testing. Submerged arc welding is

an exception; the electrode and flux come from independent lots. Thus, a

flux—electrode combination could be chosen that would not meet the mechanical property requirements even though each had been qualified separately.

In support of standards development, we are evaluating techniques for

analyzing welding fluxes. Our goal is to identify a method whereby we can

control the flux composition and possibly predict other welding problems. .

58
Thermomechariical Processing

Yi Wen Cheng

Research Leader

H . I . McHenry

D. A. Shepherd, Y. Rosenthal*

Research in thermomechanical processing uses a deformation-processing

simulator built at NIST. We study the metallurgical changes that occur in

steels during controlled rolling and accelerated cooling. By controlling

the temperature—deformat ion schedules, the cooling after rolling, and the

subsequent tempering treatment, we are striving to achieve optimum strength

and toughness in high-strength steels.

Representative Accomplishments

• The NIST thermomechanical processing (TMP) simulator was used to

study the recrystallization behavior and transformation kinetics of

a precipitation- strengthened steel.

• A dilatometer that can resolve axial displacements of 1 /im was developed to detect phase changes during accelerated cooling immediately

after deformation processing.

Thermomechanical processing simulator

A thermomechanical processing simulator has been designed and installed

[publication 3]. The simulator has the following features:

• a servohydraulic load frame with a 250-kN capacity in tension or

compression

• a dilatometer with a resolution of 1 ^m

• an actuator with a variable traveling speed up to 500 mms'" 1

• a multiple - strike capability with control - labe 1 displacements and

strain rates

*Gue s t worker from the Nuclear Research Centre Negev, Beer- Sheva, Israe 1
• a 10-kW induction heater with a maximum heating rate of 150°C-s -1

(for a cylindrical steel specimen 9 mm in diameter and 18 mm in height)

• helium-gas cooling with a maximum cooling rate of 25°C-s -1

• vacuum to 1.33 x 10~ 3 Pa (1 x 10 -5 torr) within 25 min.

It can be used to study austenite recrystallization during hot deformation,

hot-deformation resistance during single or multiple-strike deformation, and

austenite phase transformation in terms of continuous -cooling transformation

(CCT) and time—temperature—transformation diagrams. The austenite phase

transformation is detected with a dilatometer that was designed to monitor

phase changes immediately after hot working (the hot working simulates plate

rolling or forging) . Figure 26 shows temperature versus dilation for a

sample of ASTM A710 steel. The dilatometer enables us to construct CCT

diagrams from deformed austenite rather than the commonly used undeformed

austenite

TEMPERATURE, °C

Figure 26. Dilation curve for ASTM A710 steel. At(800/500°C) = 22.5 s.

60
Phase -transformation studies

A study has been made of simulated controlled rolling followed by direct

quenching (CR/DQ) of ASTM A710 steel. Experimental results indicated that

the hardenability (bainitic) of the steel was greater after CR/DQ processing than after the conventional reaustenitizing and quenching treatment

(fig. 27).

1600

LLo 1200 Qj

nc3

f—

800 <

OC

LU

400

LU

0

Figure 27. Simplified CCT diagram. The hardenability (bainitic) of ASTM

A710 steel is increased with CR/DQ processing by an extent shown

by the shaded area. The formation of polygonal ferrite is delayed about 10 s with CR/DQ processing; thus, acicular ferrite

is easier to form. The advantage of acicular ferrite is that it

is about 15 percent stronger than polygonal ferrite and nearly

as tough

With a cooling rate of about 10°C-s _1

, the sample with reaustenitizing

(910°C) and quenching treatment produced a predominantly polygonal ferrite

microstructure, the white area in Fig. 28a. The dark areas in figure 28a

are a mixture of pearlite, bainite, and martensite. With a similar cooling

rate, the processing produced the acicular ferritic microstructure shown

in figure 28b. The second-phase particles dispersed in figure 28b are a

mixture of retained austenite and martensite. Acicular ferrite is also

called granular bainite, which is different from classical bainite because

it does not contain the second-phase cementite particles.

61
The increase in hardenability is attributed to the larger austenite grain

sizes in CR/DQ-processed steel and to the dissolution of alloying elements

in the austenite. The positive implication of the observation is that the

strength of the steel can be increased with CR/DQ processing or the amounts

of alloying elements can be reduced while maintaining the same strength

level

Figure 28. Microstructures formed at a cooling rate of about 15°C*s 1 in

ASTM A710 steel. (a) conventional reaustenitized at 910°C and

quenched; polygonal ferrite dominated. (b) CR/DQ processed;

acicular ferrite dominated.

62
In-line accelerated cooling of steel plate

An advanced method of thermomechanical ly processing steel plates is to finish rolling them below their recrystallization temperature and cool them

immediately. This continuous process of controlled rolling and accelerated

cooling produces steel plates with properties in the as-rolled condition

that equal or exceed those of heat-treated plates. The steel companies in

Japan that have developed this technology have used it to produce millions

of tons of steel plate. At the present time, the U.S. steel industry does

not have the capability for in-line accelerated cooling.

To generate a domestic capability for in-line accelerated cooling, we

assisted the Department of Defense in developing a Defense Production Act

Title III Program entitled "Accelerated Cooling Processing of DOD Steels."

Three American steel-plate producers are expected to participate in Phase I

of the program, which has been funded in the fiscal year 1989 budget. The

approach is to provide incentives for the American companies to purchase

the technology and equipment from foreign companies.

This year our contribution to the Title III Program consisted mainly of

liaison activities. We visited officials at the Ministry of International

Trade and Industry and five Japanese steel companies; they agreed to cooperate in transferring the in-line accelerated cooling technology.

From three Japanese manufacturers, we obtained sample plates that were

produced by advanced thermomechanical processing for evaluation in the

United States. Their yield strengths were 450, 550, 700, and 900 MPa.

Their mechanical properties typically met specified requirements despite

significantly lower alloy contents.

63
...

V t ... I
OUTPUTS

and

INTERACTIONS

65

SELECTED RECENT PUBLICATIONS*

1. Auld, B. A.; Moulder, J. C.; Jefferies, S.; Shull, P. J. ; Ayter, S.;

Kenney, J. Eddy current reflection probes: theory and experiment.

Submitted to J. Res. Nondestruct . Eval.

2. Berge, S.; Ebrahimi, F. ; Read, D. T. Wide plates in bending: application of CTOD design approach. Read, D. T. ; Reed, R. P., eds.

Fracture Mechanics: Eighteenth Symposium. ASTM STP 945. Philadelphia: Amer. Soc. Test. Mater.; 1988. 516—534.

3. Cheng, Y.-W.; McHenry, H. I. A hot -deformation apparatus for thermomechanical processing simulation. Accepted for publication in Proceedings of the International Symposium on Physical Simulation of

Welding, Hot Forming, and Continuous Casting.

4. Cheng, Y.-W. Fatigue crack growth analysis under seawave loading.

Int. J. Fatigue 10(2): 101-108; 1988.

5. Clark, A. F. ; Reed, R. P., eds. Advances in Cryogenic Engineering —

Materials , vol. 34. New York: Plenum; 1988. 1072 pp.

6. Clark, A. V. Ultrasonic characterization of texture and formability.

Mater. Res. Soc. Bull. XIII (4): 40-43; 1988.

7. Clark, A. V.; Blessing, G. V.; Thompson, R. B. ; Smith, J. F. Ultrasonic methods of texture and monitoring for characterization of formability of rolled aluminum sheet. Thompson, D. 0.; Chimenti, D. E.

Review of Progress in Quantitative Nondestructive Evaluation , vol. 7B.

New York: Plenum; 1988. 1365—1373.

8. Clark, A. V.; Reno, R. C.; Thompson, R. B. ; Smith, J.; Blessing,

G. V.; Fields, R. J.; Delsanto, P. P. ; Mignogna, R. B. Texture monitoring in aluminum alloys: A comparison of ultrasonic and neutron

diffraction measurement. Ultrasonics 26(4): 189—197; 1988.

9. Clark, A. V.; Schramm, R. E. ; Fukuoka, H. ; Mitrakovid, D. V. Ultrasonic characterization of residual stress and flaws in cast railroad

wheels. McAvoy, B. , ed. Proceedings: IEEE 1987 Ultrasonics

Symposium. New York: IEEE; 1988. 1079-1082.

10. Datta, S. K. ; Ledbetter, H. M. ; Shindo, Y. ; Shah, A. H. ; Phase

velocity and attenuation of plane elastic waves in a particle

reinforced composite medium. Wave Motion 10: 171—182; 1988.

11. Datta, T. ; Ledbetter, H. M. ; Violet, C. E. ; Almasan, C.; Estrada, J.

Reentrant softening in perovskite-like superconductors. Phys . Rev. B

37: 7502-7505; 1988.

Papers that were published or accepted for publication by the Editorial

Review Boards of the National Institute for Standards and Technology during

fiscal year 1988.

67
12. Denys, R; McHenry, H. I. Local brittle zones in steel weldments:

an assessment of test methods. Proceedings , Seventh International

Conference on Offshore Mechanics and Arctic Engineering , vol. 3.

New York: ASME; 1988. 379-386.

13. Dodds, R. H. , Jr.; Read, D. T. Experimental and numerical studies of

the J- integral for a surface flaw. Submitted to Int . J. Fract.

14. Heerens , J.; Read, D. T. Fracture behavior of a pressure vessel

steel in the ductile to brittle transition region; NIST 88-3099.

Boulder, Colorado: National Institute of Standards and Technology;

1988.

15. Heyliger, P. R. ; Kriz, R. D. Calculation of stress intensity factors

by enriched mixed finite elements. Submitted to Conunun. Appl. Numer.

Methods

16. Heyliger, P. ; Reddy, J. A higher order beam finite element for bending and vibration problems. Submitted to J. Sound Vib.

17. Kim, Y.; Han, J. M. ; Lee, J.; Park, C.; Han, J. K. ; Reed, R. P. The

influence of aluminum and carbon on tensile behavior and microstructure in austenitic Fe—Mn—Al—C alloys. Reed, R. P. ; Xing, Z. S.;

Collings, E. W. , eds. Cryogenic Materials '88. Boulder, Colorado:

ICMC ; 1988. 481-490.

18. Kim, Y. ; Lim, C; Ryu, I.; Han, J. K. ; Reed, R. P. Low and cryogenic

temperature tensile properties of cold-rolled and precipitation

hardened copper alloy PMC-102. Reed, R. P. ; Xing, Z. S.; Collings,

E. W. , eds. Cryogenic Materials '88. Boulder, Colorado: ICMC; 1988.

693-701.

19. Kriz, R. D. ; Ledbetter, H. Graphite-magnesium- composite elastic constants representation surface. Submitted to Compos. Sci. Technol.

20. Kohn, G. ; Siewert, T. A. Dynamic arc-power source response in GMA

welding. Submitted to Weld. J.

21. Kriz, R. D. ; Sparks, L. L. Performance of alumina/epoxy thermal

isolation straps. Clark, A. F. ; Reed, R. P. , eds. Advances in

Cryogenic Engineering — Materials , vol. 34. New York: Plenum; 1988.

107-114.

22. Ledbetter, H. M. Elastic properties of metal-oxide superconductors.

J. Met. 40(1): 24-30; 1988.

23. Ledbetter, H. M. ; Austin, M. W. Deformed-polycrystalline -copper

elastic constants. Phys . Status Solidi (a) 104: 203—212; 1987.

24. Ledbetter, H. M. ; Austin, M. W. ; Kim, S. A.; Datta, T. ; Violet, C. E,

Shear-modulus change below Tc in YBa2 Cu3 0 7 _ x . J. Mater. Res. 2:

790-792; 1987.

25. Ledbetter, H. M. ; Austin, M. W. ; Kim, S. A.; Lei, M. Elastic

constants and Debye temperature of polycrystalline Y 1 Ba2 Cu3 0 7

_ x . J. Mater. Res. 2: 786-789; 1987.

26. Ledbetter, H. M. ; Kim, S. A. Low- temperature elastic constants of

deformed polycrystalline copper. Mater. Sci. Eng. 101: 87—92; 1988.

68
27 . Ledbetter, H. H. ; Kim, S. A. Molybdenum effect on Fe-Cr-Ni- alloy

elastic constants. J. Mater. Res. 3: 40-44; 1988.

28. Ledbetter, H. M. ; Kim, S. A. Low- temperature manganese contributions

to the elastic constants of face -centred- cubic Fe—Cr—Ni stainless

steel. J. Mater. Sci. 23: 2129-2132; 1988.

29. Ledbetter, H. M. ; Kim, S. A.; Austin, M. W. ; Datta, T. ; Estrada, J.;

Violet, C. E. Low- temperature elastic constants of a Y1 Ba2 Cu3 07 . x

superconductor. Submitted to Phys . Rev. B.

30. Ledbetter, H. M. ; Kim, S. A.; Capone, D. W. Elastic constants of

polycrystalline Y1 Ba2 Cu3 0 7 _ x . High -Temperature Superconductors II.

Pittsburgh: Mater. Res. Soc.; 1988. 375—378.

31. Ledbetter, H. M. ; Kim, S. A.; Datta, T. ; Estrada, J.; Violet, C. E.

Poisson- ratio anomalies in the Y1 Ba2 Cu3 0 7 . x superconductor. Submitted

to Phys. Rev. Lett.

32. Lin, I.-H. Effect of plate-like rigid inclusions on ductile/brittle

transition. Ragunta, R. , ed. Inclusions and Their Influence on

Material Behavior. Metals Park, Ohio: ASM International; 1988.

173-177.

33. Lin, I.-H.; Thomson, R. M. Relativistic BCS-OHR model. Proceedings,

Seventh International Conference on FractureNew York: Pergamon. In

press

34. Liu, S.; Siewert, T. A. Metal transfer in gas metal arc welding;

droplet frequency. Submitted to Weld. J.

35. McCowan, C. N. ; Siewert, T. A. Inclusions and fracture toughness in

stainless steel welds at 4 K. Clark, A. F. ; Reed, R. P. , eds

Advances in Cryogenic Engineering — Materials , vol. 34. New York:

Plenum; 1988. 335—342.

36. McCowan, C. N. ; Siewert, T. A.; Kivineva, E. Strength, toughness

influence of molybdenum in stainless steel welds for cryogenic

service. Proceedings , AIME Conference on Welding Metallurgy of

Structural Steels. Warrendale, Pennsylvania: Metall. Soc.; 1987.

427-438.

37. McHenry, H. I.; Purtscher, P. T. ; Shives , T. R. Observations of

hydrogen damage in a failed pressure vessel. Corrosion Sci. 27:

1041-1057; 1987.

38. Moulder, J. C. ; Nakogawa, N. ; Shull, P. T. Progress in uniform field

eddy current methods. Thompson, D. 0.; Chimenti, D. E. Review of

Progress in Quantitative Nondestructive Evaluation , vol. 7A. New

York: Plenum; 1988. 147-155.

39. Nakajima, H. ; Yoshida, K. ; Shimamoto, S.; Tobler, R. L. ; Purtscher,

P. T.; Reed, R. P. Round robin tensile and fracture test results for

an Fe—22Mn—13Cr—5Ni austenitic stainless steel at 4 K. Clark, A. F.

Reed, R. P. , eds. Advances in Cryogenic Engineering — Materials,

vol. 34. New York: Plenum; 1988. 241—249.

69
40. Ogata, T. ; Ishikawa, K. ; Reed, R. P. ; Walsh, R. P. Loading rate

effects on discontinuous deformation in load-control tensile tests.

Clark, A. F. ; Reed, R. P. , eds . Advances in Cryogenic Engineering —

Materials , vol. 34. New York: Plenum; 1988. 233—240.

41. Ogata, T. ; Ishikawa, K. ; Yuri, T.; Tobler, R. L. ; Purtscher, P. T.;

Reed, R. P. ; Shoji, T.; Nakano, K. ; Takahashi, H. Effects of specimen

size, side -grooving, and precracking temperature on J-integral test

results. Clark, A. F. ; Reed, R. P. , eds. Advances in Cryogenic

Engineering - Materials , vol. 34. New York: Plenum; 1988. 259-266.

42. Purtscher, P. T.; Reed, R. P. Influence of interstitial content on

fracture toughness. Submitted to Proceedings of the International

Conference on High Nitrogen Steels. London: Inst. Met. In press.

43. Purtscher, P. T.; Reed, R. P. ; Matlock, D. K. Metal lographic study

of the crack- tip region from fracture mechanics specimens of austenitic and ferritic steels. Submitted to Proceedings of the Materials Research Society Conference. Pittsburgh: Mater. Res. Soc.

44. Purtscher, P. T. ; Walsh, R. P. ; Reed, R. P. Fracture behavior of

316LN tensile specimen in uniaxial tension at cryogenic temperatures.

Clark, A. F. ; Reed, R. P. , eds. Advances in Cryogenic Engineering —

Materials , vol. 34. New York: Plenum; 1988. 379—386.

45. Purtscher, P. T. ; Walsh, R. P. ; Reed, R. P. Design of 316LN- type

alloys. Clark, A. F. ; Reed, R. P. , eds. Advances in Cryogenic

Engineering — Materials , vol. 34. New York: Plenum; 1988. 165—172.

46. Read, D. T. J-integral values for small cracks in steel panels.

Read, D. T. ; Reed, R. P. , eds. Fracture Mechanics: Eighteenth

Symposium. ASTM STP 945. Philadelphia: Amer. Soc. Test. Mater.;

1988. 151-163.

47. Read, D. T.; Reed, R. P. , eds. Fracture Mechanics: Eighteenth Symposium. ASTM STP 945. Philadelphia: Amer. Soc. Test. Mater.; 1988.

1117 pp.

48. Reed, R. P. Austenitic stainless steels, with emphasis on strength at

low temperatures. Walter, J. L. ; Jackson, M. R. ; Sims, C. T. , eds.

AlloyingMetals Park, Ohio: ASM International; 1988. 225—256.

49. Reed, R. P., ed. Materials Studies for Magnetic Fusion Energy Applications at Low Temperatures — XI. NBSIR 88-3082. Nat. Bur. Stand.

(U.S.); 1988. 398 pp.

50. Reed, R. P.; Xing, Z. S.; Collings, E. W. , eds. Cryogenic Materials ' 88

Boulder, Colorado: ICMC; 1988. 935 pp

51. Reed, R. P. ; McGowan, G. N. ; Walsh, R. P.; Delgado, L. A.; McColskey,

J. D. Tensile strength and ductility of indium. Mater. Sci. Eng. A

102: 227-236; 1988.

52. Reed, R. P.; Purtscher, P. T. ; Delgado, L. A. Low- temperature properties of high -manganese austenitic steels. High -Manganese Austenitic

Steels. Lula, R. A., ed. Metals Park, Ohio: ASM International; 1988.

13-22.

70
53. Reed, R. P.; Simon, N. J. Discontinuous yielding in austenitic steels

at low temperatures. Reed, R. P. ; Xing, Z. S.; Collings, E. W. , eds

Cryogenic Materials '88. Boulder, Colorado: ICMC; 1988. 851—863.

54. Reed, R. P. ; Simon, N. J. Nitrogen strengthening of austenitic stainless steels at low temperatures. Proceedings, International Conference on High Nitrogen Steels. London: Inst. Met. In press.

55. Reed, R. P.; Walsh, R. P. Tensile strain-rate effects in liquid helium. Clark, A. F. ; Reed, R. P. , eds. Advances in Cryogenic Engineering — Materials , vol. 34. New York: Plenum; 1983. 199—208.

56. Reed, R. P.; Walsh, R. P. ; Fickett, F. R. Effects of grain size and

cold rolling on cryogenic properties of copper. Clark, A. F. ; Reed,

R. P. , eds. Advances in Cryogenic Engineering — Materials, vol. 34.

New York: Plenum; 1988. 299—308.

57. Reno, R. C.; Fields, R. J.; Clark, A. V. Crystallographic texture

in rolled aluminum plates: neutron pole figure measurments. Thompson,

D. 0.; Chimenti, D. E. , eds. Review of Progress in Quantitative

Nondestructive Evaluation , vol. 7B. New York: Plenum; 1988.

1439-1445.

58. Schramm, R. E. ; Clark, A. V., Jr.; Mitracovid, D. V.; Shull, P. J.

Flaw detection in railroad wheels using Rayleigh-wave EMATs.

Thompson, D. 0.; Chimenti, D. E. eds. Review of Progress in

Quantitative Nondestructive Evaluation , vol. 7B. New York: Plenum;

1988. 1661-1668.

59. Schramm, R. E. ; Shull, P. J. ; Clark, A. V.; Mitrakovid, D. V. EMAT

examination for cracks in railroad wheel treads. Submitted to Proceedings of the Nondestructive Testing and Evaluation for Manufacturing and Construction Conference. Washington, D.C. : Hemisphere

Publishing.

60. Schramm, R. E.; Shull, P. J. ; Clark, A. V., Jr.,; Mitrackovid, D. V.

Emats for roll-by crack inspection of railroad wheels. Submitted to

Review of Progress in Quantitative Nondestructive Evaluation

61. Scull, L. L. ; Reed, R. P. Tensile and fatigue-creep properties of a

copper-stainless steel laminate. Clark, A. F. ; Reed, R. P. , eds.

Advances in Cryogenic Engineering — Materials , vol. 34. New York:

Plenum; 1988. 397-403.

62. Shimada, M. ; Tobler, R. L. ; Shoji, T. ; Takahashi, H. Specimen size,

side -grooving, and precracking effects on J- integral test results

for SUS 304 stainless steel at 4 K. Clark, A. F. ; Reed, R. P. , eds.

Advances in Cryogenic Engineering — Materials , vol. 34. New York:

Plenum; 1988. 251-258.

63. Shull, P. ; Heyliger, P, ; Moulder, J. C.; Gimple, M. ; Auld, B. A.

Applications of capacitive array sensors to nondestructive evaluation.

Thompson, D. 0.; Chimenti, D. E. Review of Progress in Quantitative

Nondestructive Evaluation , vol. 7A. New York: Plenum; 1988. 517—523.

64. Siewert, T. A. Development of a weld procedure to repair joints in

precision track. Weld. J. 67: 17—23; 1988.

71
65 . Siewert, T. A. Improved standards for real-time radioscopy. Submitted to Proceedings of the ASME Conference and Proceedings of the

Department of Defense Conference.

66. Siewert, T. A. Review of 1986 workshop: Computerization of Welding

Information. Submitted to Proceedings of the Second Conference and

Workshop on Computerization of Welding Information.

67. Siewert, T. A. Standards for real-time radiography—National Bureau

of Standards. Submitted to Proceedings, American Society for

Nondestructive Testing.

68. Siewert, T< A.; Gorni, D; Kohn, G. High-energy beam welding of type

316LN stainless steel for cryogenic applications. Clark, A. F. ; Reed,

R. P. , eds. Advances in Cryogenic Engineering — Materials , vol. 34.

New York: Plenum; 1988. 343—350.

69. Siewert, T. A.; Hicho, G. E. Choosing a welding procedure for a tenmeter- long tensile specimen. Weld. J. 67: 35—37; 1988.

70. Siewert, T. A.; Jones, J. E. ; eds. Computerization of Welding Information — Report of a Workshop Held August 5—6, 1986 in Knoxville , Tennessee. Special Publication 742. Nat. Bur. Stand. (U.S.); June

1988. 31 pp.

71. Siewert, T. A.; McGowan, C. N. The role of inclusions in the fracture

of austenitic stainless steel welds at 4 K. Koo, J. Y. , ed. Welding

Metallurgy of Structural Steels. Warrendale, Pennsylvania: Metall.

Soc.; 1987. 415-425.

72. Siewert, T. A.; McGowan, C. N. ; Olson, D. L. Prediction of ferrite

number to 100 FN in stainless steel welds. Accepted for publiction in

vol. 67 of Weld. J.

73. Siewert, T. A.; McCowan, C. N. ; Vigliotti, D. P. Cryogenic material

properties of stainless steel tube- to -flange welds. Submitted to

J. Eng. Mater. Technol.

74. Simon, N. J.; Reed, R. P. Design of 316LN-type alloys. Clark, A. F.

Reed, R. P. , eds. Advances in Cryogenic Engineering — Materials,

vol. 34. New York: Plenum; 1988. 165—172.

75. Takahashi, H. ; Shoj i , T. ; Tobler, R. L. Acoustic emission and its

applications to fracture studies of austenitic stainless steels at

4 K. Clark, A. F. ; Reed, R. P. , eds. Advances in Cryogenic Engineering — Materials

vol. 34. New York: Plenum; 1988. 387—395.

76. Tobler, R. L. ; Han, J. K. ; Reed, R. P. Fatigue resistance of a

2090-T8E41 aluminum alloy at cryogenic temperatures. Reed, R. P.

Xing, Z. S.; Collings, E. W. , eds. Cryogenic Materials '88. Boulder,

Colorado: ICMC; 1988. 703-712.

77. Tobler, R. L. ; Reed, R. P. Proposed standard method for tensile

testing of structural alloys at liquid helium temperatures. Reed,

R. P. , ed. Materials Studies for Magnetic Fusion Energy Applications

at Low Temperatures — XI. NBSIR 88-3082. Nat. Bur. Stand. (U.S.);

1988. 383-398.

72
78. Tobler, R. L. ; Reed, R. P. Proposed standard method for fracture

toughness testing of structural alloys at liquid helium temperatures.

Reed, R. P. , ed. Materials Studies for Magnetic Fusion Energy Applications at Low Temperatures — XI. NBSIR 88-3082. Nat. Bur. Stand.

(U.S.); 1988. 363-382.

79. Tobler, R. L. ; Trevisan, R. E. ; Siewert, T. A.; McHenry, H. I.;

Purtscher, P. T.; McCowan, C. N. ; Matsumoto, T. Strength, fatigue,

and toughness properties of an Fe—18Cr—16Ni—6 . 5Mn—2 .4Mo fully austenitic SMA weld at 4 K. Clark, A. F. ; Reed, R. P. , eds. Advances in

Cryogenic Engineering — Materials , vol. 34. New York: Plenum; 1988.

351-358.

80. Violet, C. E. ; Datta, T. ; Ledbetter, H. M. ; Almasen, C. ; Estrada, J.

Reentrant softening in copper-oxide superconductors. High-Temperature

Superconductors. Pittsburgh: Mater. Res. Soc.; 1988. 375—378.

81. Yoshida, K. ; Nakajima, H. ; Oshikiri, M. ; Tobler, R. L. ; Shimamoto, S.;

Miura, R. ; Ishizaka, J. Mechanical tests of large specimens at 4 K:

facilities and results. Clark, A. F. ; Reed, R. P. , eds. Advances in

Cryogenic Engineering — Materials , vol. 34. New York: Plenum; 1988.

225-232.

73
SELECTED TECHNICAL AND PROFESSIONAL COMMITTEE LEADERSHIP

American Society of Mechanical Engineers

Boiler and Pressure Vessel Code Committee

Working Group on Materials, Subgroup on NUPACK, SC III

S. Yukawa, Chairman

Journal of Applied Mechanics

R. D. Kriz, Reviewer

Materials and Structures Group

S. Yukawa, Immediate Past Vice President

American Society for Testing and Materials

E07.01: Nondestructive Evaluation

Task Force on Evaluation of Real-Time Systems

T. A. Siewert, Member

E24: Fracture Testing Committee

E24.06: Fracture Mechanics Applications

E24.06.05: Fracture Testing of Welds

H. I. McHenry, Chairman

American Welding Institute

On-line Welding Data Base Committee

T. A. Siewert

American Welding Society

Technical Papers Committee

T. A. Siewert

Welding Journal

H. I. McHenry, Reviewer

T. A. Siewert, Reviewer

Workshop on Computerization of Welding Data

Organizing Committee

T. A. Siewert

ASM International

Joining Division

T. A. Siewert, Government Liaison

Metallurgical Transactions

H. M. Ledbetter, Reviewer

Colorado School of Mines

R. D. Kriz, Adjunct Professor

Steel Research Institute Advisory Board

R. P. Reed

Defense Advanced Research Projects Agency

Advanced Submarine Technology Program

Metals Planning Group

H . I . McHenry

74
International Cryogenic Materials Conference

Board of Directors

R. P. Reed, Finance Officer

Proceedings

R. P. Reed, Coeditor

International Institute of Welding

Task Group for Elastic—Plastic Fracture -Mechanics Standard

D . T . Read

International Union of Theoretical and Applied Mechanics

Organizing Committee

H. M. Ledbetter

Metals Properties Council

Technical Advisory Committee

R. P. Reed

National Academy of Science

Materials Advisory Group of the Marine Board

T. A. Siewert

NIST—Boulder Editorial Review Board

R. L. Tobler

Superconducting Magnetic -Energy Storage

Technical Advisory Group

R. P. Reed

University of Colorado

Department of Mechanical Engineering Graduate Faculty

R. D. Kriz and H. M. Ledbetter, Adjunct Professors

U.S. Department of Energy, Office of Fusion Energy

Analysis and Evaluation Task Group

N . J . S imon

Joint U. S .—Japanese Exchange Program Advisory Committee

R. P. Reed

Low- Temperature Materials for Magnetic Fusion Energy Committee

R. P. Reed, Coordinator

Magnetics Group, Advisory Committee

R. P. Reed '

Versailles Project on Advanced Materials and Standards Task Group

Cryogenic Structural Materials Working Group

R. P. Reed

Welding Research Council

Data Base Task Group

T. A. Siewert

Materials and Welding Procedures Subcommittee

T. A. Siewert

75
AWARDS

The Bronze Medal Award for Superior Federal Service was awarded to Alfred V.

Clark, Jr. for his leadership and contributions in nondestructive evaluation

(NDE) of materials and components. He developed a strong group effort in

NDE with emphasis on measurements indicative of structural integrity and

reliability, which provide the nation with improved means of assessing the

safety of buildings, bridges, and industrial facilities.

At the joint annual meeting of the International Metallographical Society

and the American Society for Metals, two division scientists received awards

in the International Metallographic Contest. Dominique Shepherd won first

prize for her poster, Advantages of Light Microscopy for Measuring Twin

Dimensions in High-Temperature Superconductors. Chris McCowan received

honorable mention for his contribution, Micros truetural Characterization

of Y—Ba—Cu—0 superconductors.

76
INDUSTRIAL AND ACADEMIC INTERACTIONS

Industrial Interactions

Alloy Rods

T. A. Siewert informed researchers at Alloy Rods of the special precautions required for mechanical testing techniques at liquid neon

temperature

Amax Materials Research Center

H. M. Ledbetter is studying the elastic constants of pure molybdenum

for Amax Materials Research Center in Ann Arbor, Michigan. This material can undergo low- temperature magnetic transitions that may affect

the elastic constants of Fe—Cr—Ni—Mo alloys.

American Association of Railroads

For the AAR, R. E. Schramm is developing techniques to measure residual

stresses and to detect cracks in railroad wheels.

American Society for Testing and Materials

T. A. Siewert is coordinating the NIST research on standards for realtime radioscopy with the relevant ASTM subcommittees. Very close

coordination ensures that any image -quality indicators or radiationtransfer standards developed at NIST can be easily transferred to ASTM

for consideration as new standards.

American Welding Institute and American Welding Society

T. A. Siewert represents NIST on the organizing committee of the 1988

(second) Workshop on Computerization of Welding Data, which is sponsored

by NIST, AWI , and AWS . The workshop will review progress over the past

two years and develop guidelines for the welding industry in effective

use of computers

Battelle Laboratories (Columbus)

H. M. Ledbetter has long-standing collaborations with E. W. Collings on

magnetic properties of Fe—Cr—Ni—Mn alloys. Recently they agreed to reopen the studies. They are considering a joint study of the new highly metal-oxide superconductors.

CTI Cryogenics

The Welding Group advised CTI Cryogenics on sources of low- temperature

properties of solders.

77
Coldren Consulting Company

The Welding Group is working with P. Coldren on a program to develop a

new family of high- strength-high- toughness welding consumables. The

program will investigate advanced concepts in alloy systems and electrode production techniques.

Conoco

A. V. Clark, R. D. Kriz, P. T. Shull, and D. W. Fitting are working with

Conoco on the nondestructive evaluation of composites, specifically,

monitoring damage with fiber optics. R. E. Schramm provides assistance

in the use of EMATs for weld inspection.

DuPont

P. T. Shull and A. V. Clark are working with DuPont on the nondestructive evaluation of Kevlar rope.

Fax Corporation

R. E. Schramm is working with the Fax Corporation on crack inspection of

railroad wheels.

Ford Motor Company

A. V. Clark is assisting Ford in the ultrasonic measurement of forma

bility. R. D. Kriz and D. W. Fitting are helping to develop nondestructive evaluation of impact damage in composites.

Fusion Technology, Inc.

R. E. Schramm is assisting Fusion Technology in residual-stress measurement in aluminum.

Hamilton Standard

T. A. Siewert advised Hamilton Standard on sources for fatigue -crackgrowth rates in 2219 base and weld metal.

Hercules

P. T. Shull is working with Hercules on the use of eddy-current and

capacitive -array probes for nondestructive evaluation of composites.

International Institute of Welding

D. T. Read participated in a task group that developed a standard method

for reporting fracture -mechanics assessments. The standard will be submitted to the International Standards Organization for consideration as

an international standard.

78
McDonne 1 1—Douglas

J. D. McColskey is measuring the mechanical properties of graphite/PEEK

composites, which will be used on the national aerospace plane (NASP)

Perkin Elmer

H. M. Ledbetter is studying the sound velocities, thermal expansivity,

and electrical resistivity of pure beryllium at low temperatures for

Perkin Elmer in Danbury, Connecticut. Initial sound- velocity results

suggest an unexpected low- temperature transition.

Pulano Associates

T. A. Siewert advised Pulano Associates on the use of welding electrodes

and the uses of minerals in electrode formulations.

Rolled Alloys

T. A. Siewert advised Rolled Alloys on the best mechanical property

tests for characterization of stainless steel alloys at 4 K.

SCM Metal Products

H. M. Ledbetter is studying the elastic constants of alumina-dispersionstrengthened copper that is manufactured at SCM Metal Products in Cleveland, Ohio. Because the alumina particles are so small (a few hundred

angstroms) , modeling this material presents an intriguing problem.

Toray Industries (Japan)

H. M. Ledbetter, with T. Kyono , is studying the elastic constants of

graphite- fiber metal-matrix composites.

Union Pacific Railroad

R. E. Schramm is working with the Fax Corportion on crack inspection of

railroad wheels.

Welding Research Council

T. A. Siewert and J. D. McColskey assist the Materials and Welding Procedures Committee in the development of prequalified welding procedures.

The committee is composed of welding fabricators, inspection agencies,

insurance companies, sheet-metal workers, and other representatives of

the welding industry. It has produced, inspected, tested, and witnessed

welds that meet the requirements of fabrication codes. The data from

these welds are the basis for new weld-procedure specifications.

79
Joint Industrial and Academic Interactions

Colorado School of Mines

T. A. Siewert is working with H.-G. Lan and S. Liu in the study of droplet transfer in the welding arc. Present emphasis is on development of

weld- control techniques that can be implemented by computerized closedloop systems. The ultimate goal is the development of intelligent

controllers for welding processes.

Academic Interactions

Colorado School of Mines

The Welding Group, in a joint program with CSM, has analyzed the data

from about a thousand stainless steel welds and developed an improved

ferrite-prediction diagram for weld metals. The improved accuracy of

this diagram will enable the production of welds with more consistent

mechanical properties.

A. V. Clark collaborates with D. Matlock on texture and formability

research using ultrasonics.

Davidson College

H. M. Ledbetter collaborates with L. S. Cain of the Physics Department

at Davidson College in Davidson, North Carolina in experimental studies

of elastic constants. The high -temperature elastic-constant studies of

L. S. Cain complement the low- temperature studies of H. M. Ledbetter.

Currently, they are studying the carbon-plus -nitrogen alloying effects

on Fe—Cr—Ni- alloy elastic constants, which are different at different

temperatures

Harvard University

The Fracture Physics Group works with H. Gao and J. Rice in studying the

three-dimensional image force on a dislocation loops emitted from crack

tips

Iowa State University: Center for Advanced NDE, Ames Laboratories

A. V. Clark collaborates with R. B. Thompson on texture and formability

using ultrasonics.

R. D. Kriz is working with J. C. Moulder, originator of the technique,

to improve an optical -strain-measurement system.

Massachusetts Institute of Technology

The Fracture Physics Group works with A. Argon in studying the brittleto-ductile transition in cleavage fracture.

80
Osaka University

H. M. Ledbetter began a study with T. Okada on the elastic constants of

fiber-reinforced composites.

Stanford University

A. V. Clark and P. J. Shull collaborate with B. A. Auld on capacitive

array research.

Tohoku University

H. M. Ledbetter collaborates with Y. Shindo of the Mechanical Engineering Faculty on problems of waves scattered by interfaces. They use a

scattered-plane -wave ensemble -average model.

Tsinghua University

H. M. Ledbetter began a study with Y. He: the behavior of lowtemperature elastic constants and internal friction of metal-oxide

superconductors

University of Arkansas

H. M. Ledbetter, M. W. Austin, and S. A. Kim collaborate with A. M.

Hermann of the Physics Department on the physical properties of the new

high-critical- temperature metal-oxide superconductors. These properties

include electrical resistivity, magnetic susceptibility, elastic constants, and crystal structure (by x-ray diffraction). The studies focus

on substituting various trivalent rare-earth cations (R) in the compound

R 1 Ba2 Cuj 0 j _ ^

University of Belgrade

D. Mitrakovid and B. Petrovski were guest workers at NIST in the

Nondestructive Evaluation and Fracture Mechanics groups, respectively.

University of California

H. M. Ledbetter continues to work with J. Glazer and J. W. Morris, Jr.

in studying the low- temperature elastic constants of an Al—Li alloy.

University of Cambridge

H. M. Ledbetter works with P. Withers and M. Stobbs of the Metallurgy

and Materials Science Department on a theoretical problem of internal

stress in composites, stress that arises from differences in the thermal

expansivities of the particle and matrix components.

University of Colorado

H. M. Ledbetter collaborates with Professor S. Datta on theoretical

problems of waves in heterogeneous media. They recently published

several joint studies.

81
University of Geneva

Very recently, H. M. Ledbetter began working with B. Seeber to study the

elastic constants of Chevrel-phase superconductors.

University of Maryland

H. M. Ledbetter collaborates with R. Reno in studies of the effects of

texture on elastic constants.

University of Michigan

D. W. Fitting is collaborating with researchers at the University of

Michigan on the development of silicon-based acoustical arrays.

University of South Carolina

H. M. Ledbetter collaborates with T. Datta of the Physics Department on

theoretical and experimental studies of low- temperature austenitic-steel

physical properties, especially elastic constants and magnetic susceptibility. In these materials, physical properties (and perhaps plasticdeformation properties) depend on the magnetic state. They also study

the elastic and magnetic properties of the new high-critical- temperature

metal-oxide superconductors, especially Y1 Ba2 Cu3 0 7 _x, which shows large

elastic and magnetic changes.

H. M. Ledbetter collaborates with R. Edge of the Physics Department

on studies of the low- temperature magnetic state in Fe—Cr—Ni alloys.

Recently, at Oak Ridge National Laboratory, they obtained new neutrondiffraction results, which they are now trying to interpret.

University of Stuttgart

H. M. Ledbetter collaborates with E. Kroner and B. K. D. Gairola on

theoretical problems of the elastic constants of polycrystals. They

calculated the elastic constants of perfectly random polycrystalline

graphite. These new results help to explain the peculiar elastic behavior of two important technological materials: graphite fibers (used

in composites) and cast iron.

University of Tsukuba

H. M. Ledbetter collaborates with T. Suzuki on both theory and experiment of elastic constants and phase transitions. Currently, they are

exchanging ideas on metal -oxide superconductors and on a vibrating

parallelepiped elastic-constant measurement system.

With K. Otsuka, H. M. Ledbetter is studying the elastic constants of the

monocrystal shape -memory alloy Cu—Al—Ni.

University of Washington

H. M. Ledbetter collaborates with M. Taya on problems of elastic constants of and internal strain (residual stress) in composites.

82
APPENDIX

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87
N BS-1 14A (REV. 2»B0 ) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE AND SUBTITLE

PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

NISTIR 88-3841 FEBRUARY 1989

Institute for Materials Science and Engineering

Fracture and Deformation Division

Technical Activities 1988

5. AUTHOR(S)

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No.

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

8

.

Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS ( Street, City , State, ZIP)

Fracture and Deformation Division, 430

National Institute of Standards and Technology

325 Broadway

Boulder, CO 80303

10.

SUPPLEMENTARY NOTES

[^ ] Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here)

This report describes the 1988 fiscal-year programs of the Fracture and Deformation

Division of the Institute for Materials Science and Engineering. It summarizes the

principal accomplishments in three general research areas: materials performance,

properties, and processing. The Fracture Mechanics, Fracture Physics, Nondestructive

Evaluation, and Composite Materials Groups work together to detect damage in metals

and composite materials and to assess the significance of the damage with respect to

service performance. The Cryogenic Materials and Physical Properties Groups investigate the behavior of materials at low temperature and measure and model the physical

properties of advanced materials, including composites, ceramics and the new highcritical-temperature superconductors. The Welding and Thermomechanical Processing

Groups investigate the nonequilibrium metallurgical changes that occur during processing and affect the quality, microstructure, properties and performance of metals.

The report lists the division's professional staff, their research areas, publications, leadership in professional societies, and collaboration in research programs

with industries and universities.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

composites; cryogenic materials; deformation; fracture; metallurgy; nondestructive

evaluation; physical properties; steels; thermomechanical processing; welding

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

[3£] Uni i mi ted

| | For Official Distribution. Do Not Release to NTIS

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~ 20402.

85

15. Price

[~^~| Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $13.95

USCOMM-DC 6043-P80