Astm stp 1114 1991

STP 1114

Elastic-Plastic Fracture

Test Methods: The User's

Experience (Second Volume)

James A. Joyce, editor

ASTM Publication Code Number (PCN)

04-011140-30

1916 Race Street

Philadelphia, PA 19103

Downloaded/printed by

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

ASTM Publication Code Number (PCN): 04-011140-30

ISBN: 0-8031-1418-4

ISSN: 055-8497

or in part, in any printed, mechanical, electronic, film, or other distribution and storage

media, without the written consent of the publisher,

Photocopy Rights

Authorization to photocopy items for internal or personal use, or the internal or personal

use of specific clients, is granted by the AMERICAN SOCIETY FOR TESTING AND

MATERIALS for users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the base fee of $2.50 per copy, plus $0.50 per page

is paid directly to CCC, 27 Congress St., Salem, MA 01970; (508) 744-3350. For those

organizations that have been granted a photocopy license by CCC, a separate system of

payment has been arranged. The fee code for users of the Transactional Reporting Service

is 0-8031-1418-4/91 $2.50 + .50.

Peer Review Policy

Each paper published in this volume was evaluated by three peer reviewers. The authors

addressed all of the reviewers' comments to the satisfaction of both the technical editor(s)

and the ASTM Committee on Publications.

The quality of the papers in this publication reflects not only the obvious efforts of the

authors and the technical editor(s), but also the work of these peer reviewers. The ASTM

Committee on Publications acknowledges with appreciation their dedication and contribution

to time and effort on behalf of ASTM.

Printed in Baltimore, MD

August 1991

Downloaded/printed by

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

Foreword

The papers in this publication, Elastic-Plastic Fracture Test Methods; The User's Experience

(Second Volume), were presented at a symposium held in Lake Buena Vista, Florida, 8-9

November 1989. The symposium was sponsored by ASTM Committee E24 on Fracture

Testing. James A. Joyce, U.S. Navy Academy, presided as chairman and is editor of this

publication.

Downloaded/printed by

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

Contents

Overview

Experience with the Use of the New ASTM E 813-87--w. ALAN VAN DER SLUYS

AND CHARLES S. WADE

A Comparison of the J-Integral and CTOD Parameters for Short Crack Specimen

Testing--WILLIAM A. SOREM, ROBERT H. DODDS, JR., AND STANLEY T.

ROLFE

Normalization: An Experimental Method for Developing J-R Curves--ZHEN ZHOU,

KANG LEE, RUBEN HERRERA~ AND JOHN D. LANDES

Quantification of Engineering Limits to J Control of Ductile Crack Growth--JAMES

A. JOYCE

Specimen Size Requirements for Elastic-Plastic Crack Growth Resistance Curves--

J. ROBIN GORDON AND RICHARD L. JONES

A Fracture Instability Data Qualification Limit--BRUCE D. MACDONALD, R. H.

OBERDICK, AND A. L. HISER, JR.

Development of Eta Factors in Elastic-Plastic Fracture Testing Using a Load

Separation Techuique--MONIR H. SHAROBEAM, JOHN D. LANDES, AND

RUBEN HERRERA

Obtaining J-Resistance Curves Using the Key-Curve and Elastic Unloading

Compliance Methods: An Integrity Assessment Study--SABU J. JOHN

Nonincremental Evaluation of Modified J-R Curve--NAOTAKE OHTSUKA

Experience in Using Direct Current Electric Potential to Monitor Crack Growth in

Ductile MetalS--MARK P. LANDOW AND CHARLES W. MARSCHALL

Analysis of Deformation Behavior During Plastic Fracture--JUN MING HU AND

PEDRO ALBRECHT

Fracture Toughness and Fatigue Crack Initiation Tests of Welded PrecipitationHardening Stainless Steel--JOHN H. UNDERWOOD, RICHARD A. FARRARA,

G. PETER O'HARA, JOHN J. ZALINKA, AND JOHN R. SENICK

Experience with J Testing of Type 304/308 Stainless Steel Weldment--STEPHEN M.

GRAHAM, W. RANDOLPH LLOYD, AND WALTER G. REUTER

102

114

133

150

163

178

197

213

Downloaded/printed by

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

Key-Curve Analysis of Linde 80 Welds--KENNETH K. YOON, W. ALAN VAN DER

SLUYS, AND ARTHUR L. LOWE, JR.

Observations in Conducting J-R Curve Tests on Nuclear Piping Materials--

CHARLES W. MARSCHALL AND MARK P. LANDOW

Effect of Residual Stress on the J-R Curve of HY-100 Steel--ANDREA D. GALLANT,

ISA BAR-ON, AND FLOYD R. TULER

Dynamic Fracture Toughness of Modified SA508C12 in the Ductile-to-Brittle

Transition Region--MARIE T. MIGLIN, C. SCOTT WADE, JAMES A. JOYCE,

AND W. ALAN VAN DER SLUYS

Discussion

The Application of the Multispecimen J-Integral Technique to Toughened

Polymers--DONALD D. HUANG

Fracture Toughness of Polycarbonate as Characterized by the J-Integral--HENRY L.

BERNSTEIN

Determination of Jt~ for Polymer Using the Single Specimen Method--wAt N.

CHUNG ,AND JAMES G. WILLIAMS

225

238

260

273

289

290

306

320

Author Index

Subject Index

341

343

Downloaded/printed by

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

STP1114-EB/Aug. 1991

Overview

User experience with elastic-plastic test methods dates to 1981 when the first test standard

in this field, ASTM E 813-81, Jic, A Measure of Fracture Toughness, became a part of the

ASTM Standards. This original standard provided a starting point for standards development

in elastic-plastic fracture mechanics throughout the world. In 1983 the first symposium on

User's Experience with Elastic-Plastic Fracture Test Methods was sponsored by ASTM

Committee E24 and held in Knoxville, Tennessee. Papers and discussion presented at this

symposium was published in ASTM STP 856 in 1985. The work presented included not only

criticism of E 813 but also new and improved test techniques and many suggestions for

improvement of elastic-plastic test technology.

This forum of new work and criticism had direct application to the development of a

dramatically improved version of E 813 as well as the completion of a second test standard,

ASTM E 1152, Determining J-R Curves, both of which were first included in the ASTM

Book of Standards in 1987.

Much work has continued in the field of elastic-plastic fracture mechanics, and the new

work is again having a direct impact on the ASTM test standards. The Second Symposium

on User Experience with Elastic-Plastic Fracture Test Methods was held in Orlando, Florida,

in November of 1989 to again bring together the experts with experience to share in testing

of elastic-plastic and fully plastic materials. Papers presented cover experiences with the test

standards, suggestions for improvements and modifications, possible redefinition of the limits

of applicability, and applications to a range of materials including polymers. Generally the

presentations and discussions at this symposium demonstrate a higher level of satisfaction

with the E 813-87 standard than there was with the E 813-81 standard. Many suggestions

for improvements were made and will become a basis for a continued evaluation of elasticplastic test standards.

The editor would like to acknowledge the assistance of Dorothy Savini of ASTM, E. M.

Hackett and J. P. Gudas of DTRC, Annapolis, Maryland, in planning and organizing the

symposium. I thank the authors for making their presentations and submitting their formal

papers which make up this publication, and I thank the attendees whose open discussions,

questions, and comments resulted in a stimulating symposium. I especially thank the reviewers who read and critiqued the papers and who have helped me ensure a high degree

of professionalism and technical quality in this publication.

I wish to thank Portia Wells and Inez Johnson of the U. S. Naval Academy Mechanical

Engineering Department for their aid with document preparation and correspondence associated with both the symposium and this publication, and I wish to thank ASTM publications staff for their many contributions, including supplying deadlines, suggestions, and

advice during the preparation of this special technical publication.

James A. Joyce

Mechanical Engineering Department, U. S. Naval

Academy, Annapolis, MD 21402; symposium

chairman and editor.

Downloaded/printed by

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

W. Alan Van Der Sluys I and Charles S. Wade 1

Experience with the Use of the

E 813-87

New ASTM

REFERENCE: Van Der Sluys, W. A. and Wade, C. S., "Experience with the Use of the New

ASTM E 813-87," Elastic-Plastic Fracture Test Methods: The User's Experience (Second Volume), ASTM STP 1114, J. A. Joyce, Ed., American Society for Testing and Materials, Philadelphia, 1991, pp. 2-18.

ABSTRACT: In this paper the impact of recent changes in ASTM Test Method for Jlc, a

Measure of Fracture Toughness (E 813) are evaluated. J~c was determined from a large number

of J-R curves using both the 1981 and the 1987 versions of ASTM E 813. The value of Jic is

usually from 10 to 15% higher when measured according to the new version of the standard.

The scatter in the measured Jtc values was not affected by the revisions. Although the revisions

to the standard removed a number of difficulties with its use, one problem still remains to be

resolved. ASTM E 813 should be revised to include some guidance for correcting ao so that

the blunting line fits the data in the early portion of the J-R curve when a J-R curve from

ASTM Test Method for Determining J-R Curves (E 1152-87) is used.

KEY WORDS: elastic-plastic fracture, test methods, J-R curve, Jic test standards, fracture

toughness

The Jic value of a material was first defined in Ref 1 in 1972. This parameter is now used

as a measure of a material's resistance to the initiation of ductile testing. In 1981, the ASTM

issued the Test Method for Jic, a Measure of Fracture Toughness (E 813-81). This method

was extensively revised and reissued in 1987. The objective of this paper is, in part, to

evaluate the impact on measured values of Jic made by the changes to ASTM E 813 in the

1987 revision. Two major modifications were made to the ASTM E 813-81 version in creating

the ASTM E 813-87 version. The most significant involved changing the method of determining the value of Jic from the J-R curve. The 1981 version of the method uses the

intersection of the blunting line and a linear line fit to a portion of the J-R curve as the

measuring point. This procedure was changed in the 1987 version of the method to use the

intersection of a power law fit to the same portion of the data and a construction line parallel

to the blunting line that is offset by an amount representing 0.2 mm (0.008 in.) of crack

extension.

The second major revision to the 1981 version modified the equation used to evaluate J

from load, displacement, and crack length information. The expression used in the 1981

version evaluated J from the total area under the load displacement curve. The expression

was changed so that the elastic and plastic parts of J are evaluated separately in the 1987

version. The elastic term is evaluated from the elastic stress intensity, K, defined in ASTM

Test Method for Plane-Strain Fracture Toughness of Metallic Materials (E 399-83). The

plastic term is determined from the plastic portion of the area under the load displacement

1Scientist and group supervisor, respectively, Babcock & Wilcox, Research and Development Division, Alliance, OH 44601.

Copyright9 by ASTM International

Downloaded/printed by

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

VAN DER SLUYS AND WADE ON CHANGES IN ASTM E 813-87 3

curve. The combination of the modified relationship for calculating J and the new procedure

for determining Jic were intended to improve the accuracy in calculating J and decrease the

variability in Jic. Differences observed in data sets analyzed by both versions of the method

will be discussed in this paper.

In addition to the two revisions just described, ASTM issued a new standard in 1987,

ASTM Test Method for Determining J-R Curves (E 1152-87). ASTM E 813-87 allows the

use of the J-R curve determined by ASTM E 1152-87 for the determination of J~.

A second objective of this study is to evaluate problem areas that still exist in the method

and to recommend solutions to these problems. The method of correcting a0 so that the

blunting line fits data in the initial portion of the J-R curve is still a problem in the standard.

A discussion of this problem and difficulties meeting validity criteria will be included in this

paper.

Finally, various procedures for fitting mathematical models to a J-R curve will be reviewed.

The procedures will be evaluated in terms of the goodness of the fit to the J-R curve and

the ability to extrapolate the J-R curve from small-sized specimens.

Comparison of Data

The important issue to be addressed is the effect of the changes in the method on the

measured value of J~c. Difficulties were encountered with the 1981 version that were identified at the 1983 user's experience symposium [2]. One major problem with the 1981 version

was a significant variation in JIc with repeated evaluation of the same data set. By omitting

alternate points between the exclusion lines, variations in valid measures of J~c were as high

as 10% for a given test. This problem is related to the use of a linear fit to the data between

the 0.15-mm (0.006-in.) and 1.5-mm (0.060-in.) exclusion lines for the determination of JIc'

The shape of a J-R curve between the exclusion lines is often best represented by a power

law relationship rather than a linear relationship. In this situation, the linear relationship is

strongly influenced by the number and spacing of points between the exclusion lines. In the

1981 version, J~ was determined from the intersection of a linear fit to the data between

the exclusion lines and the theoretical blunting line. Therefore, J~c was also sensitive to the

number and spacing of points on the J-R curve that fell between the exclusion lines. As a

solution to this problem, the 1987 version uses a power law fit to the data between the

exclusion lines. This relationship is much less sensitive to the number and spacing of points

between the exclusion lines. The intersection of the power law fit and a construction line

define J~c. The construction line has a slope equivalent to the theoretical blunting line but

is offset by an amount representing 0.2 mm (0.008 in.) of crack extension.

A second concern identified in the 1983 symposium was scatter in JIc values obtained

from the analysis of data sets generated from testing several specimens from the same

material. The modifications made in the 1987 version of the method were intended to address

these concerns.

To reveal the changes in measured J~ values that are induced by the modifications to the

method, results from a large number of J tests were reviewed. Data generated in several

testing programs were used to make the comparisons. It was desired to evaluate test results

over a range in measured J~c values. Therefore, the data reviewed includes that obtained

from tests conducted for ORNL that were reported in Refs 3 and 4 and represent relatively

low Jic results for ferritic materials. Data obtained in a ferritic steel piping program conducted

for both Babcock & Wilcox (B&W) and the Electric Power Research Institute (EPRI) and

reported in Ref 5 was also used in the JIc comparison. This data set contained a range in

J~c results. For those tests that were conducted prior to 1987, the results were reanalyzed

using ASTIvI E 813-87 procedures. For tests completed according to the 1987 version of

Downloaded/printed by

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

4 ELASTIC-PLASTIC FRACTURE TEST METHODS

ASTM E 813, the results were reanalyzed to the 1981 version of the method. As will be

discussed later, a procedure was used that resulted in a consistent correction of the initial

crack length, a0. This correction method provides for good agreement between the data in

the initial portion of the J-R curve and the blunting line. The method described in ASTM

E 1152-87 for determination of a0 can result in inappropriate placement of the blunting line

and erroneous J~ values.

All J tests used in this comparison were conducted using the computer-controlled singlespecimen technique described in Ref 6. Load and displacement data were stored directly.

Crack length information was inferred from unloading compliance data.

The data presented in Figs. ! and 2 are used to evaluate the changes in the measured

values of J~ produced by the modifications of the method. Figure 1 presents the Jlc values

determined on seven different materials over a range in test temperatures all on the Charpy

upper shelf. The materials included in this figure are four submerged-arc-weld metals (Refs

3-5), two ferritic steels [5], and a manual metal weld [5]. In all cases, the values analyzed

to the 1987 method are higher than those calculated in accordance with the 1981 version of

the method. The difference in the submerged-arc-weld metal data ranges from a 0 to 30%

increase in the measured value of Ji~ from the 1981 to the 1987 versions. The average increase

is 11% for the 12 results reported. In the case of the ferritic materials and the manual weld,

the increase ranges from 6 to 32%. The average increase is 18% for the six values reported.

Figure 2 shows the results from two series of tests conducted at 149~ (300~ on submerged-arc-weld metal [3,4]. These two weldments were fabricated using the same welding

procedures and with the same heat of weld wire and lot of flux. They were each subjected

to identical post-weld heat treatment cycles. There is significant scatter in these test results

from each weldment. However, the difference between the results of the two test series is

not significant. Bars are shown in the figure showing the plus and minus one standard

deviation about the mean value of J~. The 1987 version of the analysis resulted in an increase

of the measured J~ value of approximately 10% as compared to the 1981 analysis. However,

use of the 1987 analysis procedure did not reduce the scatter in the measured Jlr data as

evidenced by the standard deviations.

-2500

40~ o93c } 121C V8A SUB ARC WELD

~ 149C

[3 HIGH MN MO WELD * r

SA 516-70 2000

0 sA 1o6c Z

"& E 7015-AI WELD

300

OPEN POINT E813-81 .

CLOSED POINTS E813-87 ~ 1500

. I

200

" o I 1000

[]

,W ~oo: ~* " o!, .-7

81 ,I o 500

O A&

0 i 0

MATERIAL TESTS

FIG. 1--Jlc values determined u, sing ASTM E 813-81 compared with values obtained using ASTM E

813-87 for several materials.

Downloaded/printed by

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

VAN DER SLUYS AND WADE ON CHANGES IN ASTM E 813-87 5

0 9

WELD 1

OPEN POINT E813-81

CLOSED POINTS E813-87

WELD 2

400

-350

Z k==.4

-300

-250 Z

200

-150

o 100

MATERIAL TESTS

FIG. 2--J~r values determined using ASTM E 813-81 compared with values obtained using ASTM E

813-87 for one material.

Figure 3 is a plot of the J-R curves obtained from the analysis of test data for three

specimens, from a single material, using both versions of the method. There is very little

difference in the J-R curves obtained using the two versions of the method. This similarity

indicates that the change in the J formulation yields a negligible change in a material's J-R

curve. However, the differences in the measured J~c values for the two versions of the

analyses are significant. The change in Jrc values can be attributed tothe changes in the

measuring point used for Jic determination and not the J formulation.

A detailed review of two J-R curves from a single material that exhibited a large amount

of variability in Jic was performed to determine the causes of the scatter in the JIc data.

Figure 4 presents the two J-R curves from which the J~c values for the high magnesiummolybdenum (Mn-Mo) submerged-arc-weld metal in Fig. 1 were obtained. The J~c values

obtained from these tests were 166 and 212 kJ/m 2 (947 and 1210 in..lb/in.2). While this

represents a 21% difference in the J~c value, the J-R curves are very similar. They differ

slightly in the region very close to the blunting line, yielding the difference in the measured

Jic values. The J-R curves have a steep slope between the exclusion line for these two

specimens. Large variations in J~c values would be obtained from small variations to ao. It

is conceivable that Test 3912T could easily have yielded a J~c value higher than Test 3922T

using a slightly different, but acceptable, correction to ao to obtain the best agreement

between data in the early portion of the J-R curve and the blunting line. This topic is

discussed in the next section.

The revision to ASTM E 813 invoking a power law fit rather than a linear fit to data

between the exclusion lines should improve the determination of J~c. The power law more

accurately defines the J-R curve between the exclusion lines. In addition, the revised measuring point is between the exclusion lines thereby using the power law fit to interpolate the

data to determine the Jic value. In contrast, the 81 version of ASTM E 813 makes use of

the linear fit to extrapolate the fit line to the blunting line to determine Ji~. For these reasons

the revised procedure should be less sensitive to slight changes to the data points between

Downloaded/printed by

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

6 ELASTIC-PLASTIC FRACTURE TEST METHODS

r 300

200

Aa in

-0.05 0.05 0.15 0.25 0.35 ~llll{ll~llll'llllllllJllllllllhllllllllll i

400

I00

~ * SPECIMEN I E81{-81

ff,c = 81 Kff/m

0 SPECIMEN 1 E81~-87

J~c = 85 KJ/m

+ SPECIMEN 2 E813.-81

~E J,c = 51 KJ/m"

Q O SPECIMEN 2 E81~ 87

Jlc = 74 KJ/m

~15 & SPECIMEN 3 E81~/,-81

J~c = 86 K J/m"

(~ x SPECIMEN 3 ESI~ 87

Jic = 91 KJ/m" J

-2500

2000

Z t=,=~

1500

1000 Z

500

0 ,,,,~,,l,,,lr~,,Jr,'r*l'',ll''PPll'rlrP'tl'llJllJttll'

-0.13 0.07 0.27 0.47 0.67 0.87

Aa cm

FIG. 3--J-R curve plots of ORNL V8A submerged-arc-weld metal comparing the 1981 with the 1987

version of ASTM E 813.

Aa, IN

-0.02 0.08 o.~8

o.2~

0 ._ - 4000

9 0

600

e~ -3000

dDd' I

-2000 Z

2OO - 1000

HIGH MN-MOLY WELD METAL

) = o- ~~,c = ~'~ r.J/m o

-0.5 ~.5 5.5 5.5 7.5

Aa, 1TI rrl

FIG. 4--Comparison of J-R curves yielding significantly differing Jk values for the same material.

Downloaded/printed by

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

VAN DER SLUYS AND WADE ON CHANGES IN ASTM E 813-87 7

ment. All of the J-R curves used in this study were determined using the procedures of

ASTM E 1152-87. This may have influenced the lack of observed improvements between

the 1981 and the 1987 versions of the method.

Blunting Line Data Fit

ASTM E 813 gives well-defined procedures for performing tests and reducing acquired

data to obtain Jic values. After reducing load, displacement, and crack length information

into J-integral values, the user is left to determine the critical Jic value. If the multiplespecimen procedure is used, the determination of the J~c value is well defined and adequate,

If, however, a J-R curve is determined from a single specimen using ASTM E 1152-87, a

major problem has been identified in determining an appropriate value for the initial crack

length.

ASTM E 1152-87 suggests that the crack length measured at the start of the test (using

compliance or other techniques) be compared with the optically measured initial crack length

(measured after post-test heat tinting and specimen fracture) and any errors be corrected

by determining an effective modulus value. All the crack length information used in determining the J-R curve is then corrected using this effective modulus. If there is a significant

error in the initial crack length value, the blunting line will not fit the data in the early

portion of the J-R curve and the effective modulus procedure will not improve the fit between

the blunting line and the J-R curve. Because of the small load changes required in initial

unloading compliance measurements, initial crack length values will have the largest errors

of any of the crack lengths used to determine the J-R curve. Therefore, it is important to

review the J-R curve data closely and possibly adjust the initial crack length value to obtain

the best agreement between the J-R curve and the theoretical blunting line.

Reviewing Fig. 4, it is clear that the value of Jk is strongly dependent on the placement

of the J-R curve data on the blunting line. The slope of the J-R curve may be steep in the

early portion of the curve. Significant variations in J~c would then be obtained from slight

differences in placement of the data on the blunting line.

Table 1 lists results obtained by the authors and an independent laboratory after analyzing

identical load, displacement, and crack extension data sets. Although the J-R curve data

calculated by the two laboratories were nearly identical, the differences in J~c were often

extreme. The reason for the disparity is clear upon reviewing the position of the individual

J-R curves with respect to the theoretical blunting line. The authors corrected ao to obtain

the best agreement between data in the initial portion of the J-R curve and the blunting

line. The independent laboratory simply placed the first point of the J-R curve on the blunting

line as suggested by ASTM E 1152-87. Plots of the J-R curves demonstrating the effect of

TABLE 1--Comparison of Jk measurements obtained by two separate laboratories using identical

data sets.

J~c, Author's JIc, Independent Laboratory

Data Set kJ/m 2 in.. lb/in. 2 kJ/m z in.. lb/in. 2

1 266 1519 188 1076

2 180 1028 78 448

3 268 1530 132 754

4 476 2717 296 1689

5 309 1763 85 487

6 178 1016 82 470

Downloaded/printed by

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

8 ELASTIC-PLASTIC FRACTURE TEST METHODS

correcting ao are displayed in Figs. 5 and 6. Using only one crack length value to fit the JR curve to the blunting line obviously yields incorrect Jic values in the cases discussed. More

representative values of Jic will be obtained when an attempt is made to place a number of

points from the initial portion of the J-R curve on the theoretical blunting line.

The authors have adopted a procedure for correcting ao so that the initial J-R curve data

best fit the blunting line. The data analysis computer code prompts the user to select points

on the J-R curve that define a line with a slope nearly equal to that of the blunting line.

These points are then used in a linear regression to define a new initial crack length value.

All crack length values are then adjusted to be in agreement with this new initial crack

length value. The initial test data will then scatter around the blunting line. This method

requires judgment on the part of the experimentalist in choosing which points should fall

on the blunting line. However, it forces the user to consider more than one point in the

data set when fitting data to the blunting line. When using this procedure, very little error

is usually seen between the initial crack length values measured by compliance and the

optically measured values. If an error still exists at this point, the effective modulus procedure

can be applied.

ASTM E 813 should be revised to require that a fit to more than one data point be used

to establish the initial crack length value and therefore the blunting line location when a

single-specimen J-R curve is going to be used to determine a value of Jic.

Crack Extension Requirements

ASTM E 813-87 has validity requirements relating to the uniformity of crack extension

and accuracy in the measurement of the crack extension experienced during testing. Based

on the authors' experience in conducting several hundred J tests on various materials, the

requirements described in Sections 9.4.1.6 and 9.4.1.7 are often violated.

Aa, IN

-0.008 0,012 0.052 0.052 0.072

800 ,,,,,,,ItiL4111JILIIJilIJlliJI ......... lIJlliiJ

o o9 ~ 4000

Ii 9 600 O0

o,P ~- 5000 /oo.

t~ / o 9 2000 Z

ZOO.. 9

200 o~,

1000

~CI:I:~_ AUTHORS' DATA FIT

C) ~ ~ ~ INDEPENDENT LAB DATA FIT

0 ,*l~llFr Jlr I , , , rl~ , i , , ,lllFlll , , ,I Jl~llT,~l Jlpl 0

-0.2 0.5 0.8 1.3 1.8

Aa, r.rl. 1-n

FIG. 5--Comparison of J-R curve fits to the blunting line from two laboratories.

Downloaded/printed by

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

VAN DER SLUYS AND WADE ON CHANGES IN ASTM E 813-87 9

600

400

200

Aa, IN

-o.o?,8,,,, o,.o,~?, .... o o?,2 .... o:o,s#, .... ,o,0,7?, .... o,.o??,

0 9

o, o"

0 ~~

5000 Z

2ooo I

-2

1000

~IS)S)AUTHORS' DATA FIT

INDEPENDENT LAD DATA FIT

0 C @ ill,l~llllll~,,,i,,i,,~,,,,,l~,,,,, ,,,,ll,l,,llllil,,

-o.2 o.3 o.8 1.3 1.8 2.5

Aa, ID_ II-I

FIG. 6--Comparison of J-R curve fits to the blunting line from two laboratories.

Section 9.4.1.6 relates to the uniformity of crack extension through specimen thickness.

To satisfy this Jic validity check, the crack extension at the two near-surface measuring points

must not differ from that at the center of the specimen by more than 0.02W. This criterion

is often violated using side-grooved specimens due to the crack front geometries induced

by precracking (before side grooving), side grooving, and subsequent testing. The crack

front is usually shorter at the specimen surface than in the center after fatigue precracking.

By side grooving the specimen, the crack front tends towards straightness during testing.

Often times the crack extension at the surface will then exceed that in the center by an

amount that violates Section 9.4.1.6.

The validity requirement of Section 9.4.1.6 appears to be overly restrictive considering

the flexibility given in the crack front straightness requirement of 9.4.1.5. Section 9.4.1.5

requires that any of the nine crack length measurements taken across the crack front be

within 7% of the average crack length. As a comparison of the two requirements, consider

performing a test using a 1T compact specimen containing a curved initial crack front.

Assume a typical initial average crack length of 33 mm (1.3 in.). The crack length at the

specimen surface could differ from the average by as much as 2.3 mm (0.091 in.) and still

satisfy Section 9.4.1.5. Correspondingly, the crack length at the center of the specimen could

be 2.3 mm longer or shorter than the average crack length. An example of this is shown

schematically in Fig. 7. If the crack became perfectly straight during testing, the crack

extension at the surface would be 4.6 mm (0.182 in.) larger than that at the center. This

difference is more than four times that allowed by Section 9.4.1.6, which is 1.0 mm (0.040

in.) for this example. Clearly, a discrepancy exists between these validity checks indicating

that uniformity of crack extension is more important than crack front straightness. Changing

the requirement to be based on crack front straightness and not uniformity of crack extension

should be considered.

Downloaded/printed by

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

Thư viện tri thức trực tuyến

Nội dung xem thử

Mô tả chi tiết

Tài liệu tương tự (6)

Astm stp 837 1984

Astm stp 15c 1962

Astm stp 531 1973

Astm stp 642 1978

Astm stp 849 1984

Astm stp 1601 2017