1、Designation: C1421 16C1421 18Standard Test Methods forDetermination of Fracture Toughness of Advanced Ceramicsat Ambient Temperature1This standard is issued under the fixed designation C1421; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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 These test methods cover the fracture toughness, KIc, determination of advanced ceramics at ambie
3、nt temperature. Themethods determine KIpb (precracked beam test specimen), KIsc (surface crack in flexure), and KIvb (chevron-notched beam testspecimen). The fracture toughness values are determined using beam test specimens with a sharp crack. The crack is either astraight-through crack formed via
4、bridge flexure (pb), or a semi-elliptical surface crack formed via Knoop indentation (sc), or itis formed and propagated in a chevron notch (vb), as shown in Fig. 1.NOTE 1The terms bend(ing) and flexure are synonymous in these test methods.1.2 These test methods are applicable to materials with eith
5、er flat or with rising R-curves. Differences in test procedure andanalysis may cause the values from each test method to be different. For many materials, such as the silicon nitride StandardReference Material 2100, the three methods give identical results at room temperature in ambient air.1.3 The
6、fracture toughness values for a material can be functions of environment, test rate, and temperature. These test methodsgive fracture toughness values for specific conditions of environment, test rate, and temperature.1.4 These test methods are intended primarily for use with advanced ceramics that
7、are macroscopically homogeneous andmicrostructurally dense. Certain whisker- or particle-reinforced ceramics may also meet the macroscopic behavior assumptions.Single crystals may also be tested.1.5 This standard begins with a main body that provides information on fracture toughness testing in gene
8、ral. It is followed byannexes and appendicesappendixes with specific information for the particular test methods.Main Body SectionScope 1Referenced Documents 2Terminology (including definitions, orientation and symbols) 3Summary of Test Methods 4Significance and Use 5Interferences 6Apparatus 7Test S
9、pecimen Configurations, Dimensions and Preparations 8General Procedures 9Report (including reporting tables) 10Precision and Bias 11Keywords 12Summary of ChangesAnnexesTest Fixture Geometries Annex A1Procedures and Special Requirements for Precracked BeamMethodAnnex A2Procedures and Special Requirem
10、ents for Precracked BeamMethodAnnex A2Procedures and Special Requirements for Surface Crack inFlexure MethodAnnex A3Procedures and Special Requirements for Surface Crack inFlexure MethodAnnex A3Procedures and Special Requirements for Chevron NotchFlexure MethodAnnex A41 ThisThese test method ismetho
11、ds are under the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.01on Mechanical Properties and Performance.Current edition approved Jan. 1, 2016Jan. 1, 2018. Published March 2016January 2018. Originally approved in 1999. Last previous edi
12、tion approved in 20152016 asC1421 15.C1421 16. DOI: 10.1520/C1421-16.10.1520/C1421-18.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to
13、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 ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consh
14、ohocken, PA 19428-2959. United States1Procedures and Special Requirements for Chevron NotchFlexure MethodAnnex A4AppendicesAppendixesPrecrack Characterization, Surface Crack in Flexure Method Appendix X1Complications in Interpreting Surface Crack in FlexurePrecracksAppendix X2Complications in Interp
15、reting Surface Crack in FlexurePrecracksAppendix X2Alternative Precracking Procedure, Surface Crack in FlexureMethodAppendix X3Alternative Precracking Procedure, Surface Crack in FlexureMethodAppendix X3Chamfer Correction Factors, Surface Crack in FlexureMethod OnlyAppendix X4Chamfer Correction Fact
16、ors, Surface Crack in FlexureMethod OnlyAppendix X4Crack Orientation Appendix X5Crack Orientation Appendix X51.6 Values expressed in these test methods are in accordance with the International System of Units (SI) and PracticeIEEE/ASTM SI 10.1.7 The values stated in SI units are to be regarded as st
17、andard. No other units of measurement are included in this standard.1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental
18、practices and determine theapplicability of regulatory limitations prior to use.1.9 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides an
19、d Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2C1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient TemperatureC1322 Practice for Fractography and Characterization of Fracture Origins i
20、n Advanced CeramicsE4 Practices for Force Verification of Testing MachinesE112 Test Methods for Determining Average Grain SizeE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE337 Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Te
21、mperatures)E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE740E740/E740M Practice for Fracture Testing with Surface-Crack Tension SpecimensE1823 Terminology Relating to Fatigue and Fracture TestingIEEE/ASTM SI 10 Standard for Use of the International
22、 System of Units (SI) (The Modern Metric System)2.2 Reference Material:NIST SRM 2100 Fracture Toughness of Ceramics32 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to t
23、he standards Document Summary page on the ASTM website.3 Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http:/www.nist.gov.NOTE 1The figures on the right show the test specimen cross sections and crack types. Four-point l
24、oading may be used with all three methods.Three-point may be used with the pb and vb specimens.FIG. 1 The Three Test MethodsC1421 1823. Terminology3.1 Definitions:3.1.1 The terms described in Terminology E1823 are applicable to these test methods. Appropriate sources for each definitionare provided
25、after each definition in parentheses.3.1.2 fracture toughnessa generic term for measures of resistance of extension of a crack. (E1823)3.1.3 R-curvea plot of crack-extension resistance as a function of stable crack extension.3.1.4 slow crack growth (SCG)sub critical subcritical crack growth (extensi
26、on) which may result from, but is not restrictedto, such mechanisms as environmentally-assisted environmentally assisted stress corrosion or diffusive crack growth.3.1.5 stress-intensity stress intensity factor, K FL-3/23/2the magnitude of the ideal-crack-tip stress field (stress fieldsingularity) f
27、or a particular mode in a homogeneous, linear-elastic body. (E1823)3.2 Definitions of Terms Specific to This Standard:3.2.1 back-face strainthe strain as measured with a strain gage mounted longitudinally on the compressive surface of the testspecimen, opposite the crack or notch mouth (often this i
28、s the top surface of the test specimen as tested).3.2.2 crack depth, a Lin surface-cracked test specimens, the normal distance from the cracked beam surface to the point ofmaximum penetration of crack front in the material.3.2.3 critical crack size LThethe crack size at which maximum force and catas
29、trophic fracture occur in the precracked beamand the surface crack in flexure configurations. In the chevron-notched test specimen this is the crack size at which the stressintensity factor coefficient, Y*, is at a minimum or equivalently, the crack size at which the maximum force would occur in a l
30、inearelastic, flat R-curve material.3.2.4 four-point - four-point-14-point flexureflexure configuration where a beam test specimen is symmetrically loaded at twolocations that are situated one quarter one-quarter of the overall span,span away from the outer two support bearings (see Fig.A1.1). (C116
31、1)3.2.5 fracture toughness KIc FL-3/23/2the critical stress intensity factor, Mode I, for fracture. It is a measure of the resistanceto crack extension in brittle materials.3.2.6 fracture toughness KIpb FL-3/23/2the measured stress intensity factor corresponding to the extension resistance of astrai
32、ght-through crack formed via bridge flexure of a sawn notch or Vickers or Knoop indentation(s). The measurement isperformed according to the operational procedure herein and satisfies all the validity requirements. (See Annex A2)3.2.7 fracture toughness KIscor KIsc* FL-3/23/2the measured (K(KIsc) or
33、 apparent (K(KIsc*) stress intensity factorcorresponding to the extension resistance of a semi-elliptical crack formed via Knoop indentation, for which the residual stress fielddue to indentation has been removed. The measurement is performed according to the operational procedure herein and satisfi
34、esall the validity requirements. (See Annex A3)3.2.8 fracture toughness KIvb FL-3/2the measured stress intensity factor corresponding to the extension resistance of astably-extending stably extending crack in a chevron-notched test specimen. The measurement is performed according to theoperational p
35、rocedure herein and satisfies all the validity requirements. (See Annex A4)3.2.9 minimum stress-intensity factor coeffcient, Y*minthe minimum value of Y* determined from Y* as a function ofdimensionless crack length, = a/W.3.2.10 pop-inThethe sudden formation or extension of a crack without catastro
36、phic fracture of the test specimen, apparentfrom a force drop in the applied force-displacement curve. Pop-in may be accompanied by an audible sound or other acousticenergy emission.3.2.11 precracka crack that is intentionally introduced into the test specimen prior to testing the test specimen to f
37、racture.3.2.12 stable crack extensioncontrollable, time-independent, noncritical crack propagation.3.2.12.1 DiscussionThe mode of crack extension (stable or unstable) depends on the compliance of the test specimen and test fixture;fixture, the testspecimen and crack geometries;geometries, R-curve be
38、havior of the material;material, and susceptibility of the material to slowcrack growth.3.2.13 three-point flexureflexure configuration where a beam test specimen is loaded at a location midway between twosupport bearings (see Fig. A1.2). (C1161)3.2.14 unstable crack extensionuncontrollable, time-in
39、dependent, critical crack propagation.3.3 Symbols:3.3.1 acrack depth, crack length, crack size.3.3.2 aochevron tip dimension, vb method, Fig. A4.1.C1421 1833.3.3 a1chevron dimension, vb method, (a1 = (a11 +a12)/2), Fig. A4.1.3.3.4 a11chevron dimension, vb method, Fig. A4.1.3.3.5 a12chevron dimension
40、, vb method, Fig. A4.1.3.3.6 a0.25crack length measured at 0.25B, pb method, Fig. A4.2.3.3.7 a0.50crack length measured at 0.5B, pb method, Fig. A4.2.3.3.8 a0.75crack length measured at 0.75B, pb method, Fig. A4.2.3.3.9 a/Wnormalized crack size.3.3.10 Bthe side to side side-to-side dimension of the
41、test specimen perpendicular to the crack length (depth) as shown in Fig.A2.4, Fig. A3.7, and Fig. A4.1.3.3.11 ccrack half width, sc method, Fig. A3.7.3.3.12 dlength of long diagonal for a Knoop indent, length of a diagonal for a Vickers indent, sc method.3.3.13 Eelastic modulus.3.3.14 f(a/W)function
42、 of the ratio a/W, pb method, four-point flexure, Eq A2.6.3.3.15 Findent force, sc method.3.3.16 FCchamfer correction factor, sc method.3.3.17 g(a/W)function of the ratio a/W, pb method, three-point flexure, Eq A2.2 and Eq A2.4.3.3.18 hdepth of Knoop or Vickers indent, sc method, Eq A3.1.3.3.19 H1(a
43、/c, a/W)a polynomial in the stress intensity factor coefficient, for the precrack periphery where it intersects the testspecimen surface, sc method, Eq A3.7.3.3.20 H2(a/c, a/W)a polynomial in the stress intensity factor coefficient, for the deepest part of a surface crack, sc method,see Eq A3.5.3.3.
44、21 KIstress intensity factor, Mode I.3.3.22 KIcfracture toughness, critical stress intensity factor, Mode I.3.3.23 KIpbfracture toughness, pb method, Eq A2.1 and Eq A2.3.3.3.24 KIscfracture toughness, sc method, Eq A3.9.3.3.25 KIvbfracture toughness, vb method, Eq A4.1.3.3.26 Ltest specimen length,
45、Fig. A2.1 and Fig. A3.1.3.3.27 L1, L2precracking fixture dimensions, pb method, Fig. A2.2.3.3.28 M(a/c, a/W)a polynomial in the stress intensity factor coefficient, sc method, see Eq A3.4.3.3.29 Pforce.3.3.30 Pmaxforce maximum.3.3.31 Q(a/c)a polynomial function of the surface crack ellipticity, sc m
46、ethod, Eq A3.3.3.3.32 S(a/c, a/W)factor in the stress intensity factor coefficient, sc method, Eq A3.8.3.3.33 Soouter span, three- or four-point test fixture. Figs. A1.1 and A1.2.3.3.34 Siinner span, four-point test fixture, Fig. A1.1.3.3.35 tnotch thickness, pb and vb method, Fig. A2.3 and Fig. A4.
47、1.3.3.36 Wthe top to bottom top-to-bottom dimension of the test specimen parallel to the crack length (depth) as shown in A2.4,A3.7, and A4.1.3.3.37 Ystress intensity factor coefficient.3.3.38 Y*stress intensity factor coefficient for vb method.3.3.39 Ymaxmaximum stress intensity factor coefficient
48、occurring around the periphery of an assumed semi-elliptical precrack,sc method.3.3.40 Y*minminimum stress intensity factor coefficient, vb method, Eq A4.2-A4.5.3.3.41 Ydstress intensity factor coefficient at the deepest part of a surface crack, sc method, Eq A3.2.3.3.42 Ysstress intensity factor co
49、efficient at the intersection of the surface crack with the test specimen surface, sc method,Eq A3.6.C1421 1844. Summary of Test Methods4.1 These methods involve application of force to a beam test specimen in three- or four-point flexure. The test specimen is verysimilar to a common flexural strength test specimen. The test specimen either contains a sharp crack initially (pb, sc) or developsone during loading (vb). The equations for calculating the fracture toughness have been establis
