Astm stp 463 1970

REVIEW OF DEVELOPMENTS IN PLANE STRAIN FRACTURE TOUGHNESS TESTING W F Brown, Jr., editor ASTM SPECIAL TECHNICAL PUBLICATION 463 List price $18.25 AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street, Philadelphia, Pa 19103 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized (~) BY AMERICANSOCIETYFOR TESTING AND MATERIALS1970 Library of Congress Catalog Card Number: 72-97728 ISBN 0-8031-0058-2 NOTE The Society is not responsible, as a body, for the statements and opinions advanced in this publication Printed in LutherviUe-Timonium, Md September 1970 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Foreword The object of this book is to bring together a series of papers which describe recent experience obtained in the United States and in England with the application of the ASTM E-24 Proposed Method of Test for Plane Strain Fracture Toughness of Metallic Materials This information supplements that which has appeared in ASTM STP 381 on Fracture Toughness Testing and its Application and in STP 410 on Plane Strain Crack Toughness Testing of High Strength Metallic Materials This publication is a cooperative effort of ASTM and NASA NASA research personnel have participated in ASTM Fracture Committee activities since their inception in 1959 This participation reflects the strong interest that NASA has maintained in the development of test methods for evaluation of the fracture resistance of engineering materials This interest arises from the necessity for the use of high-strength alloys in critical parts of aerospace structures By cooperation with ASTM in publication of this book NASA is helping to fulfill its obligation to provide the widest practicable and appropriate dissemination of results from its activities George C Deutsch Assistant Director for Materials Sciences and Engineering, NASA Headquarters, Washington, D C Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions autho Related ASTM Publications Fracture Toughness Testing and Its Applications, STP 381 (T965), $19.50 Plane Strain Crack Toughness Testing of High Strength Metallic Materials, STP 410 (1967), $5.50 Electron Fractography, STP 436 (1968), $11.00 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Contents PAGE Introduction to STP 463 w F BROWN, JR P r o g r e s s in F r a c t u r e T e s t i n g o f M e t a l l i c M a t e r i a l s - - J G KAUEMAN Theory Initial Recommendations Thickness as a Problem Fatigue Cracking Emphasis on Thick Sections Evolution of Notched Bend Specimens C o m p a c t K~c S p e c i m e n Screening Tests Thin-Section Problem Medium-Strength Materials Cautionary Notes Summary 4 12 15 15 18 18 18 20 Evaluation of a Method of Test for Plane Strain Fracture Toughness Testing U s i n g a B e n d S p e c i m e n - - R H H E Y E R A N D D E MC CABE Pilot Program Interlaboratory Tests Fatigue Cracking Bend Testing A n a l y s i s o f K~c D a t a Conclusions 23 23 24 30 33 40 B r i t i s h E x p e r i e n c e w i t h P l a n e S t r a i n F r a c t u r e T o u g h n e s s (KIt) T e s t i n g - M J MAY Collaborative Test Program First Stage Second Stage S t a n d a r d i z a t i o n o f KIc T e s t i n g Influence of Fatigue Precracking Conditions Crack Length-Specimen Thickness Requirements Draft British Standard Summary Discussion 42 43 43 44 47 47 51 61 61 62 T h e I n f l u e n c e o f C r a c k L e n g t h a n d T h i c k n e s s in P l a n e S t r a i n F r a c t u r e T o u g h n e s s T e s t s - - M H JONES AND W F BROWN, JR Material and Specimen Preparation Test Procedure Analysis of Data Bend Specimens Smooth Specimens Results for Effects of Thickness and Crack Length S c r e e n i n g T e s t s f o r K~c C o r r e l a t i o n o f K~c w i t h T e n s i l e P r o p e r t i e s Practical Significance of Results Appendixes Discussion 63 66 67 68 68 71 72 77 84 85 88 92 22 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduction vi CONTENTS PAGE C r a c k T o u g h n e s s Testing o f High-Strength Steels E, A STEIGERWALD N o t c h Bend Tests Km D a t a for High-Strength Steels S u m m a r y a n d Conclusions Discussion 102 107 113 115 121 Slow Bend K~c Testing o f M e d i u m - S t r e n g t h H i g h - T o u g h n e s s Steels s T 124 t25 128 R O L F E A N D S R, N O V A K Materials a n d Procedure Specimen G e o m e t r y a n d Analysis Results a n d Discussion Kio Values Pop-in Criteria Specimen Size R e q u i r e m e n t s Effects o f Stress Level D u r i n g Fatigue Cracking Effect o f Face N o t c h i n g Correlation Between Krc a n d C V N Values S u m m a r y a n d Conclusions 131 131 133 139 144 145 145 147 Application o f Fracture Mechanics T e c h n o l o g y to M e d i u m - S t r e n g t h S t e e l s - W G C L A R K , J R , A N D E T W E S S E L I n f o r m a t i o n R e q u i r e d in Fracture Mechanics T e c h n o l o g y Material Properties Discussion o f Materials Properties Example P r o b l e m General Stress Analysis Calculation o f Critical Flaw Sizes Calculation o f Cyclic Life Material Selection D e v e l o p m e n t o f Inspection Criteria a n d Safety F a c t o r s Summary Discussion 160 161 162 172 177 180 180 182 184 185 186 188 F r a c t o g r a p h i c Analysis o f the L o w Energy F r a c t u r e o f an A l u m i n u m A l l o y - J P T A N A K A , C A P A M P I L L O , A N D J R L O W , J R Material F r a c t o g r a p h i c Study Failure o f Large Inclusions Transmission Electron Microscopy Identification o f Void-Nucleating Particles Discussion F r a c t o g r a p h i c Observation o f Boundary Between Fatigue C r a c k a n d Dimpled Rupture Conclusions Appendix C o m m e n t a r y on Present P r a c t i c e - - w F B R O W N , J R , A N D J E S R A W L E Y Specimen Size R e q u i r e m e n t s Fundamental Concepts Effects o f Plastic D e f o r m a t i o n in K~c, Tests Face G r o o v i n g Specimen Preparation and Test Procedure Crack Starter Configuration and Displacement Gage Length 191 192 193 196 200 204 207 210 214 214 216 217 219 221 226 227 227 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions aut CONTENTS vii PAGE Fatigue Cracking Nonuniformities in Fatigue Cracks Fatigue Crack Sharpness Requirement Testing of Brittle Material C o m p a r i s o n of Plane Strain Fracture Toughness of Various Alloys Correlation of KIc with Other Properties Correlation with Tensile Properties Tensile Ductility in Material Specifications Correlation with Impact Properties Fracture Tests with Subsized Specimens (Screening Tests) Material Selection for Particular Applications Acceptance Tests Alloy Development Tests Tentative M e t h o d o f Test for Plane Strain Fracture Toughness of Metallic Materials ( A S T M Designation: E 399-70 T) 228 228 229 231 232 238 238 240 241 243 244 244 246 249 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions author STP463-EB/Sep 1970 Introduction This Special Technical Publication brings together a set of papers that were presented at a Panel Session on Plane Strain Crack Toughness sponsored by the ASTM E-24 Committee on Fracture Testing of Metals during the 1968 ASTM Annual Meeting in San Francisco The main purpose of this Panel Session was to review the practical experience in fracture toughness testing which had developed since ASTM Committee E-24 placed its major efforts in standardization on methods of test for plane strain fracture toughness These efforts were started early in 1965, and the initial developments were described in A S T M S T P 410.1 The paper by Kaufman reviews these developments and gives a brief history of ASTM Committee E-24 activity In the latter part of 1966 Subcommittee I of ASTM Committee E-24 on High Strength Metallic Materials formulated a Proposed Recommended Practice for Plane Strain Fracture Toughness Testing of High Strength Materials Using a Fatigue-Cracked Bend Specimen Draft copies of this document were made available early in 1967, and during the next year and a half considerable experience was gained in applying the Proposed Practice to a wide variety of metallic materials During this trial period various practical problems were encountered, some due to tke inherent limitations of elastic crack mechanics and others associated with certain details of specimen preparation and testing The members of the Panel, who all had well-established fracture testing programs, were asked to emphasize these problem areas As a result of this Panel meeting and subsequent discussions among the ASTM E-24 Comimttee members several changes were made in the Recommended Practice, and a revised document was published in the 1969 A S T M B o o k o f Standards This revision incorporated a compact tension specimen as well as the bend specimen, and was designated as a Proposed Method of Test for Plane Strain Fracture Toughness of Metallic Materials This Proposed Method was subsequently further revised as described in the concluding contribution to this STP and was advanced to a Tentative Method (E 399-70T), a copy of which has been bound at the back of this volume Since the papers which appear in this STP were presented, ASTM Committee E-24 Method of Test has been incorporated into various specifications issued by both the U S Government and by private industry It forms t Brown, W F., Jr., and Srawley, J E., Plane Strain Crack Toughness Testing of High Strength Metallic Materials, ASTM STP 410, American Society for Testing and Materials, 1966 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Copyright9 1970by ASTMlntcrnational www.astm.org Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized PLANE STRAIN FRACTURE TOUGHNESS TESTING a part of the Aerospace Material Document series issued by the Society of Automotive Engineers and is also the basis far qualifying KIe data for incorporation into MIL-Hdk-5 These applications have revealed certain aspects of the Test Method which could be improved, but, what is more important, they have shown that there is a strong desire on the part of many investigators to compromise what they consider to be the overly strict specimen size requirements Suggestions that the required crack length or specimen thickness or both could be reduced appear in several of the papers o f this volume This concern about specimen size arises naturally out of attempts to apply the Test Method to materials having lower strength and higher toughness than those originally intended by the ASTM E-24 Committee This volume contains two contributions that were not part of the Panel Session on Plane Strain Crack Toughness The first is a paper by J R Low, Jr., and his associates describing some recently completed work on the fractographic analysis of the aluminum alloy 2014-T6 This paper is quite pertinent since it provides a plausible explanation for the relatively low plane strain fracture toughness characteristic of this and possibly other high-strength aluminum alloy plate The second is a contribution by J E Srawley and myself entitled "Commentary on Present Practice." This not only summarizes the salient features of the various papers, but also attempts to clarify certain aspects of plane strain fracture toughness testing where there appears to be some confusion W F Brown, Jr Chief, Strength of Materials Branch, National Aeronautics and Space Administration-Lewis Research Center, Cleveland, Ohio 44135 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized TENTATIVE METHOD OF TFST 255 Specimen Configuration, Dimensions, and Preparation 6.1 Specimen Size 6.1.1 In order for a result to be considered valid according to this method it is required that both the specimen thickness, B, and the crack length, a, exceed 2.5 (Kic/avs) ~, where ~YS is the 0.2 percent offset yield strength of the material for the temperature and loading rate of the test [1,4,5] 6.1.2 The initial selection of a size of specimen from which valid values of K~c will be obtained may be based on an estimated value of K~c for the material It is recommended that the value of KI c be overestimated, so that a conservatively large specimen will be employed for the initial tests After a valid KI~ result is obtained with the conservative-size initial specimen, the specimen size may be reduced to an appropriate size [a and B > 2.5 (Kt~/ ~ys) 2] for subsequent testing 6.1.3 Alternatively the ratio of yield strength to Young's modulus can be used for selecting a specimen size that will be adequate for all but the toughest materials: ays/E 0.0050 0.0057 0.0062 0.0065 0.0068 0.0071 0.0075 0.0080 0.0085 0.0100 to to to to to to to to to or 0.0057 0.0062 0.0065 0.0068 0.0071 0.0075 0.0080 0.0085 0.0100 greater Minimum Recommended Thickness and Crack Length in mm 21/2 13`4 11/2 11/4 3,4 75 63 50 44 38 32 25 20 1/4 121/2 I/2 61/2 When it has been established that 2.5 ( K i r is substantially less than the minimum recommended thickness given in the preceding table, then a correspondingly smaller specimen can be used On the other hand, if the form of the available material is such that it is not possible to obtain a specimen with both crack length and thickness greater than 2.5 (K~c/~vs) 2, then it is not possible to make a valid KI r measurement according to this recommended method 6.2 Standard Specimens The geometry of standard specimens is shown in Fig 4, bend specimens, and Fig 5, compact tension specimens, with notch details in Fig Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 256 PLANESTRAIN FRACTURETOUGHNESSTESTING W -+ 010 -T- Crack Starter Envelope( See Fig b and Section6.2 ) ~=(, A ~ W_+ 002 ~- L A.~ t,ill , : a=k~ 11 3_ 2W+ O.lW rain -~ - 2W+ O.lW rain NOTE Dimensions and tolerances are in inches unless otherwise indicated NOTE "A" surfaces are to be perpendicular to center line of crack-starter envelope within • TIR NOTE Integral or attachable knife edges for clip gage attachment may be used (see Fig and 6.2.5) METRIC EQUIVALENTS U.S Customary Units, in 0.002 0.005 0.010 Metric Equivalents, mm 0.05 0.13 0.25 FIG Bend specimen standard proportions and tolerances (not a working drawing) 6.2.1 The crack length, a, is nominally equal to thickness, B, and is between 0.45 and 0.55 times the depth, W 6.2.2 The crack-starter slot configuration must lie within the envelope, shown in Fig 6, that has its apex at the end of the fatigue crack 6.2.3 The length of the fatigue crack shall be not less than percent of the overall length, L, and not less than 0.05 in (1.3 ram) 6.2.4 To facilitate fatigue cracking at a low level of stress intensity (see 6.5) the notch root radius should be 0.003 in (0.08 mm) or less However, if a chevron form of notch is used, as shown in Fig 6b, the notch root radius may be 0.01 in (0.25 ram), or less 6.2.5 Attachable or integral knife edges for fixing the clip gage to the specimen shall be provided as shown by the suggested designs in Figs 7a and 7b, respectively The displacements will be essentially independent of the gage length for the bend specimen providing the gage length is equal to or less than W / For the compact tension specimen the displacements will be essentially independent of the gage length for any length up to 1.2W A design for attachable knife edges is shown in Fig 7a This design is based on the gage length requirement for the bend specimen and a knife edge spacing of Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduc TENTATIVE METHOD OF TEST 2.57 0.2 in (5.1 ram) The effective gage length is established by the points o f contact between the screw and hole threads F o r the design shown the m a j o r diameter o f the screw has been used in setting this gage length The No screw will permit attachable knife edges to be used for specimens having W < in (76 mm) A No screw will permit the use of attachable knife edges for specimens having W > in (51 mm) It will be recognized that more flexibility is possible in the design of attachable knife edges for the c o m p a c t tension specimen because the gage length may extend to 1.2W .25W • 0(]6 Dia Holes, Note - ~ Crack Starter ~, T ~ Envelope ( See Fig - ~ ~ andSecli0n6.2) Nx,x I J~ ~t ~ J~ ~l~[ ~ ~'J'~J I A-~ c_-_ - W+.O02 i- _j L B= -I + ,1.25W+.005 NOTF I Dimensions and tolerances in inches NOTE "A" and "C" surfaces are to be perpendicular and parallel as applicable t o within 0.002-in TIR For specimens of ay, > 200 ksi the holes may be 0.3 W q- 0.005 NOTE Integral or attachable knife edges for clip gage attachment may be used (see Fig and 6.2.5) METRIC EQUIVALENTS U.S Customary Units, in 0.002 0.005 0.010 Metric Equivalents, mm 0.05 0.13 0.25 FIG Compact tension specimen standard proportions and tolerances (not a working drawing) Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 258 PLANESTRAIN FRACTURE TOUGHNESS TESTING I Specimen Edge Recl~iredEnvelo~ (a) N =~ L = 45 to 55Wfor Bend Specimens L = 0.10 to 0.80W for CompactSpecimens Examples T Chevron T Straight Thru ,,,LT FatigueCrack Shall Be N~ LessI~aa~" Percent of Length.L, Nor Less 0.05 inch ~ Keyhole [| NoT~ Dimensions are in inches METRIC EQUIVALENTS U.S Customary Units, in 0.05 Metric Equivalents, mm 1.3 FIG 6. Envelope for crack-starter notches and examples of notches tipped with fatigue cracks 6.3 Alternative Specimens The form of available material may be better adapted to alternate specimen shapes than to the standard specimen with B = 0.5W 6.3.1 Alternative bend specimens may have B = 0.25W to W 6.3.2 Alternative compact tension specimens may have B = 0.25W to 0.5W 6.3.3 Crack length, a, shall be 0.45 to 0.55 W, the same as for the standard specimen 6.3.4 The support span, S, for the bend specimen shall be 4W, the same as for the standard specimen 6.3.5 The size requirements of 6.1 shall be met, as for the standard specimens Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduct TENTATIVEMETHOD OF TEST 6.4 Other Designs of Compact Tension Specimens Other designs of compact tension specimens are in use, particularly in nuclear reactors for monitoring long-term irradiation damage When such specimens are prepared and tested in accordance with the procedure of this test method the validity of the results can be judged on the same basis as for specimens of standard geometry, namely, as specified in 8.1 In reporting results from such specimens the appropriate expression for calculation of K~ from toad and specimen dimensions should be stated and its origin cited [4] 6.5 Fatigue Cracking The fatigue cracking shall be conducted with the specimen fully heat treated to the condition in which it is to be tested (Note 3) The fatigue crack is to be extended from the notch at least 0.05 in (1.3 mm) I I J 07 06 2C + Screw Ihd Dia < W - Knife Edge Width -IX = Clip Gage Arm Width, rain I\ - - I I I " fL Specimen _ L \ \ _ J _ _ i ] I / I / I / Screw Hd Dia I/ 60o" c O.100 in | J/_ 9032 in rain / _ _ Notch Centerline ~ NoTE Dimensions and tolerances are in inches METRIC EQUIVALENTS U.S Customary Units, in 0.032 0.06 0.07 0,10 Metric Equivalents, mm 0.81 1.5 1.8 2,5 FIG 7a Example of attachable knife edge design based on the gage length requirements for the bend specimen Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 260 PLANESTRAIN FRACTURE TOUGHNESS TESTING I I I Crack Starter Envelope ( See Fig, ) I I I I I I ~ - N -'1 I I I I I ~ 06 o.8 _0.200 0.195 Noa~l Dimensions are in inches NOtE -Gage length shown is for W_< in but it may be any value up to W/4 (see 6.2.5) METRIC EQUIVALENTS U S Customary Units, in 0.050 0.060 0.195 0.200 Metric Equivalents, mm 1.3 1.5 5.0 0.1 FIG 7b -Integral knife edges and sufficiently far to meet the requirements of 6.2, 6.3, or 6.4 T o determine when this requirement has been met in practice, it is usually sufficient to observe the traces of the crack on the side surfaces of the specimen T o ensure that the fatigue crack will be sufficiently sharp, flat, and n o r m a l to the specimen edge, the following conditions of fatigue cracking shall be met: 6.5.1 The equipment for fatigue cracking shall be such that the load distribution is symmetrical with relation to the notch, and the m a x i m u m value o f the stress intensity in the fatigue cycle shall be k n o w n with an error o f not more than percent [6] 6.5.2 D u r i n g the final stage of fatigue crack extension, for at least the terminal 2.5 percent of the overall length of notch plus crack, the ratio o f the m a x i m u m stress intensity of the fatigue cycle to the Y o u n g ' s modulus, Kj(max)/E, shall not exceed 0.0012 in 1/2 (0.000192 m~/2) Furthermore, Ks Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions author TENTATIVE METHOD OF TEST 261 (max) must not exceed 60 percent of the KQ value determined in the subsequent test if KQ is to qualify as a valid K~c result (see 8.1) 6.5.3 The stress-intensity range should be not less than 0.9 Kj(max) Fatigue cycles that involve reversal of loading are of no particular advantage but may be expedient with certain types of equipment The K calibration is very sensitive to the distribution of clamping forces which are necessary to grip the specimen for reversed-load cycling Particular care must be taken that the K calibration for the fatigue setup properly represents the applied clamping forces 6.5.4 When fatigue cracking is conducted at a temperature T1 and testing at a different temperature 7'2, Kj(max) must not exceed (~ysl/2 avs2)KQ, where aYsl and avs~ are the yield strengths at the respective temperatures T1 and T2 NOTE Some materials are too brittle to be fatigue cracked without fracturing These materials are outside the scope of the present standard test method NOTE The K calibration is the relationship of stress-intensity factor K to load and specimen dimensions [1] For example, see 8.1.3 and 8.1.4 Procedure 7.1 Number of Tests It is recommended that at least three replicate tests be made NOTE Information on variability of test results will be found in Ref 1, pages 26 and 74, and Ref 7.2 Specimen Measurement All specimen dimensions shall be within the tolerances shown in Figs 1, 2, and 7.2.1 Measure the thickness, B, to the nearest 0.001 in (0.025 ram) or I percent, whichever is larger, at not less than three positions between the fatigue-crack tip and the unnotched edge of the specimen, and record the average value 7.2.2 F o r a bend specimen, measure the depth, IV, and the crack length, a from the notched edge of the specimen to the far edge, and to the crack front, respectively For a compact specimen, measure these dimensions from the plane of the center line of the loading holes (the notched edge is a convenient reference line but the distance from the center line of the holes to the notched edge must be subtracted to determine W and a) Measure the depth, W, to the nearest 0.001 in (0.025 ram) or 0.I percent, whichever is larger, at not less than three positions near the notch location, and record the average value 7.2.3 After fracture measure the crack length to the nearest 0.5 percent at the following three positions: at the center of the crack front, and midway between the center and the end of the crack front on each side Use the average of these three measurements as the crack length to calculate Ko (see 8.1.3 and 8.1.4) If the difference between any two of the crack length measurements Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduc 262 PLANESTRAIN FRACTURE TOUGHNESS TESTING exceeds percent of the average, or if any part of the crack front is closer to the machined notch root than percent of the average crack length, or 0.05 in (1.3 ram) minimum, then the test is invalid Also if the length of either surface trace of the crack is less than 90 percent of the average crack length, as defined above, the test is invalid 7.2.4 If the fatigue crack departs noticeably from the plane of symmetry of the notch, measure the greatest angle between the fatigue crack surface and the plane of symmetry If this angle exceeds 10 deg the test is invalid 7.3 Bend Testing Set up the bend test fixture so that the line of action of the applied load shall pass midway between the support roll centers within 0.5 percent of the distance between these centers (for example, within 0.02 in (0.5 mm) for a 4-in (100-mm) span) Measure the span to within 0.5 percent of nominal length Locate the specimen with the notch center line midway between the rolls to within 0.5 percent of the span, and square to the roll axes within deg Seat the displacement gage on the knife edges to maintain registry between knife edges and gage grooves In the case of attachable knife edges, seat the gage before the knife edge positioning screws are tightened Load the specimen at a rate such that the rate of increase of stress intensity is within the range 30,000 to 150,000 psi in.1/2/min (0.55 to 2.75 MN-m-3/2/s), corresponding to a loading rate for the in thick specimen between 4000 and 20,000 lb/min (0.03 to 0.15 kN/s) 7.4 Tension Testing Eliminate friction effects, and also eccentricity of loading introduced by the clevis itself, by adherence to the specified tolerances for the specimen clevis and pins shown in Fig Eccentricity of loading can also result from misalignment external to the clevis, or from incorrect positioning of the specimen with respect to the center of the clevis opening Obtain satisfactory alignment by keeping the center line of the upper and lower loading rods coincident within 0.03 in (0.76 mm) during the test and by centering the specimen with respect to the clevis opening within 0.03 in (0.76 mm) Seat the displacement gage in the knife edges to maintain registry between the knife edges and the gage groove In the case of attachable knife edges, seat the gage before the knife edge positioning screws are tightened Load specimens at a rate such that the rate of increase of stress intensity is within the range 30,000 to 150,000 psi.in.1/2/min (0.55 to 2.75 MN.m-3/2/s) corresponding to a loading rate for the 1-in.-thick specimen between 4500 and 22,500 lb/rnin (0.034 to 0.17 kN/s) 7.5 Test Record Make a test record consisting of an autographic plot of the output of the load-sensing transducer versus the output of the displacement gage The initial slope of the linear portion shall be between 0.7 and 1.5 It is conventional to plot the load along the vertical axis, as in an ordinary tension test record Select a combination of load-sensing transducer and autographic recorder so that the load, PQ, (see 8.1) can be determined from Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduct TENTATIVE METHOD OF TEST 263 the test record with an accuracy of -4-1 percent With any given equipment, the accuracy of readout will be greater the larger the scale of the test record Calculation and Interpretation of Results 8.1 Interpretation of Test Record and Calculation of Kz~ In order to establish that a valid K~ c has been determined, it is necessary first to calculate a conditional result, KQ which involves a construction on the test record, and then to determine whether this result is consistent with the size and yield strength of the specimen according to 6.1 Referring to Fig 8, the procedure is as follows: I On the test record draw the secant line OPz through the origin with a slope percent less than the slope of the tangent OA to the initial part of the record (Note 6) Ps is the load at the intersection of the secant with the record Next, determine the load PQ which will be used to calculate KQ as follows: if the load at every point on the record which precedes Ps is lower than Ps, then PQ is equal to Ps (Fig 8, Type 1); if, however, there is a maxim u m load preceding Ps which exceeds it, then this maximum load is PQ (Fig 8, Types II and III) NOTE Slightnonlinearity at the very beginning of a record often occurs during seating of the specimen and the gage, and should be ignored However, it is important to establish the initial slope of the record with high precision, and therefore it is advisable to minimize this nonlinearity by a preliminary loading and unloading with the maximum load not producing a stress intensity level exceeding that used in the final stage of fatigue cracking NOTE: SLOPE OP5 IS EXAGGERATED FOR CLARITY A A /j XI ~ .,=~ A /// , O fTYPEIII x'-7]%P=~ r , x, = o.G r DISPLACEMENT GAGE OUTPUT FIG Principal types of load-displacement records Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 264 PLANESTRAIN FRACTURE TOUGHNESS TESTING 8.1.2 Draw a horizontal line representing a constant load of 0.8 Ps Measure the distance X1 along the horizontal line from the tangent OA to the record, and measure the corresponding horizontal distance to Ps If the ratio of the deviation from linearity at 0.8 Ps to that at Ps is greater than 0.25, then the test is not a valid K~c test [4] Proceed to calculate KQ in order to estimate a revised specimen size, but not report KQ as a valid K~ r 8.1.3 For the bend test calculate KQ from PQ as follows: PQSI2.9(~)a/z KQ BW 3/~ 4.6 (W)a/2 q- 21.8 ( ~ ) 5n - - (W)V2 + 38.7 ( ~ ) ' ~ where: Po B S W a = = = = = load as determined in 8.1.1, lb, thickness of specimen, in., span length, in., depth of specimen, in., and crack length as determined in 7.2.3, in 8.1.3.1 When using SI units with PQ in newtons and dimensions in millimeters the above expression for Ko should be multiplied by 0.0348 8.1.3.2 To facilitate calculation of KQ, values of the power series given in brackets in the above expressions are tabulated in the following table for specific values of a/IV a/IV f(a[W) a/W f(a/W) 0.450 0.455 0.460 0.465 0.470 0.475 0.480 0.485 0.490 0.495 2.28 2.32 2.35 2.39 2.42 2.46 2.50 2.54 2.58 2.62 0.500 0.505 0.510 0.515 0.520 0.525 0.530 0.535 0.540 0.545 0.550 2.66 2.70 2.75 2.79 2.84 2.89 2.94 2.99 3.04 3.09 3.15 8.1.4 For the tension test calculate KQ from Po as follows: KQ BW '/2P~ I29.6 ( W ) 1/~- 185.5 ( ~ ) at2 q- 655.7 ( ~ ) ~/2 - - 1 ( ~ ) V ~ + 638.9 ( ~ ) / ~ Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized TENTATIVE METHOD OF TEST 265 where: PQ = load as determined in 8.1.1, lb, B = thickness of specimen, in., W = width of specimen, in., and a - crack length as determined in 7.2.3, in 8.1.4.1 W h e n using SI units with PQ in newtons and dimensions in millimeters the above expression for Ko should be multiplied by 0.0348 8.1.4.2 T o facilitate calculation o f KQ, values Of the power series given in brackets in the above expressions are tabulated below for Specific values o f a/w alW f(a[W) alW f(a/W) 0.450 0.455 0.460 0.465 0.470 0.475 0.480 0.485 0.490 0.495 8.34 8.45 8.57 8.69 8.81 8.93 9.06 9.19 9.33 9.46 0.500 0.505 0.510 0.515 0.520 0.525 0.530 0.535 0.540 0.545 0.550 9.60 9.75 9.90 10.05 10.21 10.37 10.54 10.71 10.89 11.07 11.26 8.1.5 Calculate 2.5 (Kq/ays) I f this quantity is less than both the thickness and the crack length o f the specimen, then KQ is equal to Ktr Otherwise it is necessary to use a larger specimen to determine KIr in order to satisfy this requirement The increase in dimensions can be estimated on the basis o f KQ 8.2 Fracture Appearance The appearance of the fracture is valuable supplementary information and shall be noted for each specimen C o m m o n types o f fracture appearance are shown in Fig F o r fractures o f Types a or b, measure the average width, f, o f the central flat fracture area, and note and record the proportion of oblique fracture per unit thickness (B f ) / B M a k e this measurement at a location midway between the crack tip and the unnotched edge o f the specimen R e p o r t fractures o f Type c as full oblique fractures Report 9.1 The report shall include the following for each specimen tested: ! Thickness, B, 9.1.2 Depth, W, Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authoriz 266 PLANESTRAIN FRACTURETOUGHNESS TESTING NOICH OR a OR b c FRACTION PREDOMINANT FULL OBLIQUE OBLIQUE OBLIQUE FIG Common types o f fracture appearance 9.1.3 Fatigue precracking conditions in terms of: 9.1.3.1 Maximum stress intensity, Ki(max) and number of cycles for terminal fatigue crack extension over a length at least 2.5 percent of the overall length of notch plus crack, and 9.1.3.2 The stress intensity range for terminal crack extension, 9.1.4 Crack length measurements, 9.1.4.1 At center of crack front, 9.1.4.2 Midway between the center and the end of the crack front on each side, and 9.1.4.3 At each surface 9.1.5 Test temperature, 9.1.6 Relative humidity as determined by ASTM Method E 337, for Determining Relative Humidity by Wet- and Dry-Bulb Psychrometer,a 9.1.7 Loading rate in terms of Ks (change in stress intensity factor per unit time), 9.1.8 Load-displacement record and associated calculations, 1969 Book o f A S T M Standards, Part 30 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized TENTATIVE METHOD OF TEST 267 9.1.9 F r a c t u r e appearance, 9.1.10 Yield strength, a n d 9.1.11 KIe APPENDIX A1 DOUBLE CANTILEVER CLIP-IN DISPLACEMENT GAGE AI.1 The gage consists of two cantilever beams and a spacer block which are clamped together with a single nut and bolt, as shown in Fig Electrical-resistance strain gages are cemented to the tension and compression surfaces of each beam, and are connected as a Wheatstone bridge incorporating a suitable balancing resistor The material for the gage beams should have a high ratio of yield strength to elastic modulus, and titanium alloy 13V-11Cr-3A1 in the solution treated condition has been found very satisfactory for this purpose If a material of different modulus is substituted, the spring constant of the assembly will change correspondingly, but the other characteristics will not be affected Detailed dimensions for for the beams and spacer block are given in Figs A1 and A2 For these particular dimensions the useful operating range of the assembly is from 0.15 to 0.30 in (3.8 to 7.6 mm) The range can be altered by substituting a spacer block of appropriate height As discussed in 5.4, the precision of the gage corresponds to a maximum deviation of • in (0.0025 mm) of the displacement readings from a least-squares best-fit straight line through the data Further details concerning design, construction and use of these gages are given in Ref References [1] Brown, W F., Jr., and Srawley, J E., Plane Strain Crack Toughness Testing of High Strength Metallic Materials, ASTM STP 410, ASTTA, American Society for Testing and Materials, 1966 [2] Srawley, J E., "Plane Strain Fracture Toughness," Fracture, Vol 4, Chapter 2, pp 45-68 [3] Fracture Toughness Testing and Its Applications, A S T M STP 381, ASTTA, American Society for Testing and Materials, April 1965 [4] Wessel, E T., "State of the Art of the WOL Specimen for K~c Fracture Toughness Testing," Engineering Fracture Mechanics, Vol 1, No 1, Jan 1968 [5] Srawley, J E., Jones, M H., and Brown, W F., Jr., "Determination of Plane Strain Fracture Toughness," Materials Research and Standards, MIRSA, American Society for Testing and Materials, Vol 7, No 6, June 1967, p 262 [6] Fisher, D M and Repko, A J., "Note on Inclination of Fatigue Cracks in Plane Strain Fracture Toughness Test Specimens," Materials Research and Standards, MIRSA, American Society for Testing and Materials, Vol 9, No 4, April 1969 [7] Jones, M H., Bubsey, R T., and Brown, W F., Jr., "Clevis Design for Compact Tension Specimens Used in K~o Testing," Materials Research and Standards, MIRSA, American Society for Testing and Materials, Vol 9, No 5, May 1969 [8] Heyer, R H and McCabe, D E., "Evaluation of a Method of Test for Plane-Strain Fracture Toughness Using A Bend Specimen," Research Laboratory, Armco Steel Corp Middletown, Ohio [9] Fisher, D M., Bubsey, R T., and Srawley, J E., "Design and Use of a Displacement Gage for Crack Extension Measurements," NASA TN-D-3724, NASNA, National Aeronautics and Space Administration, 1966 Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 268 PLANESTRAIN FRACTURETOUGHNESS TESTING 1.6275 t.620 9/64 DRILL FOR - NC SCREW 0.375 0.041 0.020 R ~ 0.039 o.~ I"= re) m "\\ / / ~ _ 0.065 ~o'-~\ \,o l I I O.OZi 0.060 / J NotrE Dimensions are in inches METRIC EQUIVALENTS U.S Metric U.S Metric Customary Equivalents, Customary Equivalents, U n i t s , in mm U n i t s , in mm 1.52 0.004 0.10 0.060 0.006 0.15 0.065 1.65 0.010 0.25 9/64 3.6 019 0.48 0.186 4.72 0.020 0.51 0.188 4.78 0.021 0.53 0.370 9.40 0.025 0.64 0.373 9.47 0.030 0.76 0.375 9.52 0.039 0.99 1.620 41.15 0.041 1.04 1.625 41.28 FIG AI Beams for double-cantilever displacement gage Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproduction TENTATIVEMETHOD OF TEST 5/64 DRILL ~ - - ~ z 269 ~ ~ HOLES ~II ~ I o.19o 0'166 /~ / / ~ o I , o.o93 oo I IYi " ~ f " UNDERCUT 0,050 0.045 45~ CHAMFER 9/64 DRILL FOR / 32 NC SCREW N o T E - - D i m e n s i o n s a r e in inches METRIC U.S Customary U n i t s , in FIG EQUIVALENTS Metric Equivalents, mm U.S Customary U n i t s , in Metric Equivalents, mm 1/32 0.045 0.80 1.14 0.195 0.205 4.95 5.21 0.050 5/64 0.087 1.27 2.00 2.21 0.373 0.375 0.376 9.47 9.52 9.55 0.093 0.125 9/64 0.186 0.188 0.190 2.36 3.18 3.60 4.72 4.78 4.83 0.378 0.400 0.402 0.490 1/2 0.500 9.60 10.t6 10.21 12.45 12.70 12.70 A2 Spacer block for double-cantilever displacement gage Copyright by ASTM Int'l (all rights reserved); Mon Dec 13:19:19 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized