1、Designation: B909 00 (Reapproved 2011)B909 17Standard Guide forPlane Strain Fracture Toughness Testing of Non-StressRelieved Aluminum Products1This standard is issued under the fixed designation B909; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers supplementary guidelines for plane-strain fracture toughness testing o
3、f aluminum products for whichcomplete stress relief is not practicable. Guidelines for recognizing when residual stresses may be significantly biasing test resultsare presented, as well as methods for minimizing the effects of residual stress during testing. This guide also provides guidelinesfor co
4、rrection and interpretation of data produced during the testing of these products. Test Method E399 is the standard testmethod to be used for plane-strain fracture toughness testing of aluminum alloys.1.2 This standard does not purport to address all of the safety concerns, if any, associated with i
5、ts use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.1.3 This international standard was developed in accordance with internationally recognized principles on standardiz
6、ationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E399 Test Method for Linear-Elastic Plane-Strain Frac
7、ture Toughness KIc of Metallic MaterialsE561 Test Method forKR Curve DeterminationE1823 Terminology Relating to Fatigue and Fracture Testing2.2 ANSI Standard:ANSI H35.1 Alloy and Temper Designations for Aluminum32.3 ISO Standard:ISO 12737 Metallic MaterialsDetermination of Plane Strain Fracture Toug
8、hness43. Terminology3.1 DefinitionsTerminology in Test Method E399 and Terminology E1823 are applicable herein.3.2 Definitions of Terms Specific to This Standard:3.2.1 corrected plane-strain fracture toughness a test result, designated Kq Q (corrected), which has been corrected for residualstress bi
9、as by one of the methods outlined in this guide. The corrected result is an estimation of the Kq or KIc that would have beenobtained in a residual stress free specimen. The corrected result may be obtained from a test record which yielded either an invalidKq or valid KIc, but for which there is evid
10、ence that significant residual stress is present in the test coupon.3.2.1.1 DiscussionThe corrected result is an estimation of the KQ or KIc that would have been obtained in a residual stress free specimen. The1 This guide is under the jurisdiction of ASTM Committee B07 on Light Metals and Alloys an
11、d is the direct responsibility of Subcommittee B07.05 on Testing.Current edition approved Nov. 1, 2011May 1, 2017. Published June 2012June 2017. Originally approved in 2000. Last previous edition approved in 20062011 as B909 00(2006).(2011). DOI: 10.1520/B0909-00R11.10.1520/B0909-17.2 For referenced
12、ASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St.
13、, 4th Floor, New York, NY 10036, http:/www.ansi.org.4 Available from International Organization for Standardization (ISO), 1 rue de Varemb, Case postale 56, CH-1211, Geneva 20, Switzerland, http:/www.iso.ch.This document is not an ASTM standard and is intended only to provide the user of an ASTM sta
14、ndard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by AS
15、TM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1corrected result may be obtained from a test record which yielded either an invalid KQ or valid KIc, but for which there is evidencethat sign
16、ificant residual stress is present in the test coupon.3.2.2 invalid plane-strain fracture toughness a test result, designated KqQ, that does not meet one or more validityrequirements in Test Method E399 or ISO 12737 and may or may not be significantly influenced by residual stress.3.2.3 valid plane-
17、strain fracture toughness a test result, designated KIc, meeting the validity requirements in Test MethodE399 or ISO 12737 that may or may not be significantly influenced by residual stress.4. Significance and Use4.1 The property KIc, determined by Test Method E399 or ISO 12737, characterizes a mate
18、rials resistance to fracture in aneutral environment and in the presence of a sharp crack subjected to an applied opening force or moment within a field of highconstraint to lateral plastic flow (plane strain condition).AKIc value is considered to be a lower limiting value of fracture toughnessassoc
19、iated with the plane strain state.4.1.1 Thermal quenching processes used with precipitation hardened aluminum alloy products can introduce significant residualstresses in the product. Mechanical stress relief procedures (stretching, compression) are commonly used to relieve these residualstresses in
20、 products with simple shapes. However, in the case of mill products with thick cross-sections (for example, heavy gageplate or large hand forgings) or complex shapes (for example, closed die forgings, complex open die forgings, stepped extrusions,castings), complete mechanical stress relief is not a
21、lways possible. In other instances residual stresses may be unintentionallyintroduced into a product during fabrication operations such as straightening, forming, or welding operations.4.1.2 Specimens taken from such products that contain residual stress will likewise themselves contain residual str
22、ess. Whilethe act of specimen extraction in itself partially relieves and redistributes the pattern of original stress, the remaining magnitudecan still be appreciable enough to cause significant error in the ensuing test result.4.1.3 Residual stress is superimposed on the applied stress and results
23、 in an actual crack-tip stress intensity that is different fromthat based solely on externally applied forces or displacements.4.1.4 Tests that utilize deep edge-notched specimens such as the compact tension C(T) are particularly sensitive to distortionduring specimen machining when influential resi
24、dual stress is present. In general, for those cases where such residual stresses arethermal quench induced, the resulting KIc or KqQ result is typically biased upward (that is, KqQ is higher than that which wouldhave been achieved in a residual stress free specimen). The inflated values result from
25、the combination of specimen distortion andbending moments caused by the redistribution of residual stress during specimen machining and excessive fatigue precrack fromcurvature5.4.2 This guide can serve the following purposes:4.2.1 Provide warning signs that the measured value of KIc has been biased
26、 by residual stresses and may not be a lower limitvalue of fracture toughness.4.2.2 Provide experimental methods by which to minimize the effect of residual stress on measured fracture toughness values.4.2.3 Suggest methods that can be used to correct residual stress influenced values of fracture to
27、ughness to values thatapproximate a fracture toughness value representative of a test performed without residual stress bias.5. Warning SignsInterferences5.1 There are a number of warning signs that test measurements are or might be biased by the presence of residual stress. Ifany one or more of the
28、 following conditions exist, residual stress bias of the ensuing plane strain fracture toughness test resultshould be suspected. The likelihood that residual stresses are biasing test results increases as the number of warning signs increase.5.1.1 A temper designation of a heat treatable aluminum pr
29、oduct that does not indicate that it was stress relieved. Stress reliefis indicated by any of the following temper designations: T_51, T_510, T_511, T_52, or T_54, as described in ANSI H35.1.5.1.2 Machining distortion during specimen preparation. An effective method to quantify distortion of a C(T)
30、specimen is tomeasure the specimen height directly above the knife edges (typically at the front face for specimen designs with integral knifeedges) prior to and after machining the notch. Experience has shown that for an aluminum C(T) specimen with a notch length towidth ratio (a(ao/W)/W) of 0.45,
31、a difference in the height measured before and after machining the notch equal to or greater than0.003 in. (0.076 mm) is an indicator that the ensuing test result will be significantly influenced by residual stress.5.1.3 Excessive fatigue precrack front curvature not meeting the crack-front straight
32、ness requirements in Test Method E399 orISO 12737.5.1.4 Unusually high loads or number of cycles required for precracking relative to the same or similar alloy/products.5.1.5 A significant change in fracture toughness that is greater than that typically observed upon changing specimenconfiguration (
33、for example, from C(T) to three point bend bar) or upon changing specimenspecimens planW sizedimension thatcannot be explained by other means. For example, if residual stress is biasing fracture toughness tests results, then increasing thespecimenspecimens planW sizedimension typically results in in
34、creasing KqQ values.5 Bucci, R.J., “Effect of Residual Stress on Fatigue Crack Growth Rate Measurement,” Fracture Mechanics: Thirteenth Conference, ASTM STP 743,American Society forTesting and Materials, 1981, pp. 2847.B909 172NOTE 1Other factors, such as a steeply rising R-curve (Practice E561) in
35、high toughness alloy/products, may also be responsible for KqQ valuesincreasing with increasing specimen planW size.dimension.5.1.6 A nonlinear load-COD trace during the initial elastic portion of the test record. This result is indicative of the residualstress clamping that is being overcome to ope
36、n the crack under the progressively increasing applied load.6. Minimizing Effects of Residual Stress on Fracture Toughness Measurements6.1 When testing aluminum products that have not been stress relieved, there are two approaches available to minimize oreliminate the effects of residual stress on f
37、racture toughness measurements. The first approach involves the use of one or moreexperimental methods designed to minimize the residual stress in test specimens.The second approach involves the use of post-testcorrection methods to estimate the fracture toughness KqQ or KIc that would have been obt
38、ained had the test specimen been freeof residual stress.7. Experimental Methods to Minimize Effects of Residual Stress7.1 The following considerations can be used to minimize the magnitude of residual stress in test specimens.7.1.1 To minimize the biasing influences of both distortion-induced clampi
39、ng (or opening) moments and precrack frontcurvature, the specimen thickness (B)(B) should be as small as possible with respect to the host product thickness, whilemaintaining a specimen W/B ratio of 2. However, this must be done such that the specimen B and W dimensions are large enoughto meet the T
40、est Method E399 or ISO 12737 specimen size requirements for valid KIc measurement.7.1.2 In cases where the specimen size required to obtain a valid KIc is too large for the strategy described in 7.1.1 to beeffective, the use of special precracking techniques can produce a straighter fatigue precrack
41、 and reduce the residual stress bias.One such technique involves the use of high stress ratios for precracking. Experience has shown that precracking at a cyclic stressratio of 0.7 results in significantly straighter crack fronts than precracks produced at a stress ratio of 0.1. Moreover, the straig
42、htercrack fronts that result from precracking at higher R-ratio have been shown to reduce the error in the ensuing fracture toughnessmeasurement by up to 75 %.NOTE 2Test Method E399 requires precracking to be performed at stress ratios between 1 and 0.1 (inclusive). Therefore, specimens precracked a
43、tstress ratios greater than 0.1 and less than or equal to 0.7 will result in KqQ, which are invalid in accordance withTest Method E399. However, even thoughinvalid, the KqQ obtained from a specimen precracked at higher stress ratios but meeting the crack front straightness requirements and other val
44、idityrequirements in Test Method E399 should be a significantly better estimate of the plane-strain fracture toughness, KIc, than an invalid KqQ obtained froma specimen precracked at a stress ratio meeting Test Method E399 requirements but with excessive crack front curvature.7.1.3 Measurement of th
45、e specimen height change, as depicted in Fig. 1, can be used as a gage of the severity of the bendingmoment induced residual stress bias. The measurements can also be used as a method to estimate the “true” fracture toughnessthrough a post-test correction described in Section 8.8. Post-Test Residual
46、 Stress Correction Methods8.1 Method 1This correction method utilizes the specimen height change measurement described in Fig. 1 and denoted as .As shown in Fig. 2, the origin of the residual stress biased load-displacement test record is modified by displacing the origin byan amount equal to and to
47、 the load associated with that displacement. The test is now analyzed using this new origin andmodified load-displacement record with the standard methodology described in Test Method E399.NOTE 1Measure the specimen height before and after machining the crack starter notch.FIG. 1 Residual Stress Cor
48、rection Practice for KIc Testing of C(T) SpecimensB909 173NOTE 3Limited experimental evidence6,7 indicates that under precracking conditions resulting in excessive crack front curvature (that is, not meetingthe crack front straightness requirements in Test Method E399), Kq Q (corrected) values obtai
49、ned by Method 1 are within 15 % of the KIc or KqQ valuethat would have been obtained in a residual stress free specimen. Limited experimental evidence also indicates that the accuracy of the correction methoddecreases when the specimen has been precracked at higher stress ratios, such as 0.7, to obtain a straighter crack front. In this case, Method 2 is preferred.8.2 Method 2A second empirical residual correction method involves the use of a modified fatigue precrack length in thecalculation of KqQ. For this correction method, the fatigue precrack length
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