1、Designation: C 1421 01b (Reapproved 2007)Standard Test Methods forDetermination of Fracture Toughness of Advanced Ceramicsat Ambient Temperature1This standard is issued under the fixed designation C 1421; the number immediately following the designation indicates the year oforiginal adoption or, in
2、the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the fracture toughness deter-mination of KIpb(precracked b
3、eam test specimen), KIsc(surfacecrack in flexure), and KIvb(chevron-notched beam test speci-men) of advanced ceramics at ambient temperature. Thefracture toughness values are determined using beam testspecimens with a sharp crack. The crack is either a straight-through crack (pb), or a semi-elliptic
4、al surface crack (sc), or itis propagated in a chevron notch (vb).NOTE 1The terms bend(ing) and flexure are synonymous in these testmethods.1.2 These test methods determine fracture toughness valuesbased on a force and crack length measurement (pb, sc), or aforce measurement and an inferred crack le
5、ngth (vb). Ingeneral, the fracture toughness is determined from maximumforce. Applied force and displacement or an alternative (forexample, time) are recorded for the pb test specimen and vbtest specimen.1.3 These test methods are applicable to materials witheither flat or with rising R-curves. The
6、fracture toughnessmeasured from stable crack extension may be different thanthat measured from unstable crack extension. This differencemay be more pronounced for materials exhibiting a risingR-curve.NOTE 2One difference between the procedures in these test methodsand test methods such as Test Metho
7、d E 399, which measure fracturetoughness, KIc, by one set of specific operational procedures, is that TestMethod E 399 focuses on the start of crack extension from a fatigueprecrack for metallic materials. In these test methods the test methods foradvanced ceramics make use of either a sharp precrac
8、k formed via bridgeflexure (pb) or via Knoop indent (sc) prior to the test, or a crack formedduring the test (vb). Differences in test procedure and analysis may causethe values from each test method to be different. Therefore, fracturetoughness values determined with these methods cannot be interch
9、angedwith KIcas defined in Test Method E 399 and may not be interchangeablewith each other.1.4 These test methods give fracture toughness values, KIpb,KIsc, and KIvb, for specific conditions of environment, test rateand temperature. The fracture toughness values, KIpb,KIsc, andKIvbfor a material can
10、 be functions of environment, test rateand temperature.1.5 These test methods are intended primarily for use withadvanced ceramics which are macroscopically homogeneous.Certain whisker- or particle-reinforced ceramics may also meetthe macroscopic behavior assumptions.1.6 These test methods are divid
11、ed into three major partsand related sub parts as shown below. The first major part is themain body and provides general information on the testmethods described, the applicability to materials comparisonand qualification, and requirements and recommendations forfracture toughness testing. The secon
12、d major part is composedof annexes that provide procedures, test specimen design,precracking, testing, and data analysis for each method. AnnexA1 describes suggested test fixtures, Annex A2 describes thepb method, Annex A3 describes the sc method, and Annex A4describes the vb method. The third major
13、 part consists of threeappendices detailing issues related to the fractography andprecracking used for the sc method.Main Body SectionScope 1Referenced Documents 2Terminology (including definitions, orientation and symbols) 3Summary of Test Methods 4Significance and Use 5Interferences 6Apparatus 7Te
14、st Specimen Configurations, Dimensions and Preparations 8General Procedures 9Report (including reporting tables) 10Precision and Bias 11AnnexesTest Fixture Geometries A1Special Requirements for Precracked Beam Method A2Special Requirements for Surface Crack in Flexure Method A3Special Requirements f
15、or Chevron Notch Flexure Method A4AppendicesPrecrack Characterization, Surface Crack in Flexure Method X1Complications in Interpreting Surface Crack in Flexure Precracks X2Alternative Precracking Procedure, Surface Crack in FlexureMethodX31.7 Values expressed in these test methods are in accordancew
16、ith the International System of Units (SI) and Practice E 380.1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 .Current edition approved Feb. 1, 2007. Published March 2007. Originallyapproved in 1999. Last p
17、revious edition approved in 2001 as C 1421 - 01b.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1.8 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the
18、 user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient TemperatureC 1322 Practice for Fract
19、ography and Characterization ofFracture Origins in Advanced CeramicsE4 Practices for Force Verification of Testing MachinesE112 Test Methods for Determining Average Grain SizeE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 337 Test Method for Measuring Humidity with a Psy
20、-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E 399 Test Method for Linear-Elastic Plane-Strain FractureToughness KIcof Metallic MaterialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 740 Practice for Fracture Testing with Surface
21、-CrackTension SpecimensE 1823 Terminology Relating to Fatigue and Fracture Test-ingIEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI) (The Modern Metric System)2.2 Reference Material:NIST SRM 2100 Fracture Toughness of Ceramics33. Terminology3.1 Definitions:3.1.1 The terms des
22、cribed in Terminology E 1823 are ap-plicable to these test methods. Appropriate sources for eachdefinition are provided after each definition in parentheses.3.1.2 crack extension resistance, KRFL-3/2, GRFL-1, orJRFL-1,a measure of the resistance of a material to crackextension expressed in terms of
23、the stress-intensity factor, K,strain energy release rate, G, or values of J derived using theJ-integral concept. (E 1823)3.1.3 fracture toughnessa generic term for measures ofresistance of extension of a crack. (E 399, E 1823)3.1.4 R-curvea plot of crack-extension resistance as afunction of stable
24、crack extension.3.1.5 slow crack growth (SCG)sub critical crack growth(extension) which may result from, but is not restricted to, suchmechanisms as environmentally-assisted stress corrosion ordiffusive crack growth.3.1.6 stress-intensity factor, K FL-3/2the magnitude ofthe ideal-crack-tip stress fi
25、eld (stress field singularity) for aparticular mode in a homogeneous, linear-elastic body.(E 1823)3.2 Definitions of Terms Specific to This Standard:3.2.1 back-face strainthe strain as measured with a straingage mounted longitudinally on the compressive surface of thetest specimen, opposite the crac
26、k or notch mouth (often this isthe top surface of the test specimen as tested)3.2.2 crack depth, a Lin surface-cracked test speci-mens, the normal distance from the cracked beam surface tothe point of maximum penetration of crack front in thematerial.3.2.3 crack orientationa description of the plane
27、 anddirection of a fracture in relation to a characteristic direction ofthe product. This identification is designated by a letter orletters indicating the plane and direction of crack extension.The letter or letters represent the direction normal to the crackplane and the direction of crack propaga
28、tion.3.2.3.1 DiscussionThe characteristic direction may beassociated with the product geometry or with the microstruc-tural texture of the product.3.2.3.2 DiscussionThe fracture toughness of a materialmay depend on the orientation and direction of the crack inrelation to the material anisotropy, if
29、such exists. Anisotropymay depend on the principal pressing directions, if any, appliedduring green body forming (for example, uniaxial or isopress-ing, extrusion, pressure casting) or sintering (for example,uniaxial hot-pressing, hot isostatic pressing). Thermal gradi-ents during firing can also le
30、ad to microstructural anisotropy.3.2.3.3 DiscussionThe crack plane is defined by letter(s)representing the direction normal to the crack plane as shownin Fig. 1, Fig. 2, and Fig. 3. The direction of crack extension isdefined also by the letter(s) representing the direction parallelto the characteris
31、tic direction (axis) of the product as illustratedin Fig. 1b, Fig. 2b and Fig. 3b.HP = hot-pressing direction (See Fig. 1)EX = extrusion direction (See Fig. 2)AXL = axial, or longitudinal axis (if HP or EX are not applicable)R = radial direction (See Fig. 1, Fig. 2 and Fig. 3)C = circumferential dir
32、ection (See Fig. 1, Fig. 2 and Fig. 3)R/C = mixed radial and circumferential directions (See Fig. 3b)3.2.3.4 DiscussionFor a rectangular product, R and Cmay be replaced by rectilinear axes x and y, corresponding totwo sides of the plate.3.2.3.5 DiscussionDepending on how test specimens aresliced out
33、 of a ceramic product, the crack plane may becircumferential, radial, or a mixture of both as shown in Fig. 3.3.2.3.6 Identification of the plane and direction of crackextension is recommended. The plane and direction of crackextension are denoted by a hyphenated code with the firstletter(s) represe
34、nting the direction normal to the crack plane,and the second letter(s) designating the expected direction ofcrack extension. See Fig. 1, Fig. 2 and Fig. 3.3.2.3.7 DiscussionIn many ceramics, specification of thecrack plane is sufficient.3.2.3.8 Isopressed products, amorphous ceramics, glassesand gla
35、ss ceramics are often isotropic, and crack plane orien-tation has little effect on fracture toughness. Nevertheless, thedesignation of crack plane relative to product geometry isrecommended. For example, if the product is isopressed (either2For referenced ASTM standards, visit the ASTM website, www.
36、astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1
37、070, http:/www.nist.gov.C 1421 01b (2007)2cold or hot) denote the crack plane and direction relative to theaxial direction of the product. Use the same designationscheme as shown in Figs. 1 and 2, but with the letters “AXL”to denote the axial axis of the product.3.2.3.9 If there is no primary produc
38、t direction, referenceaxes may be arbitrarily assigned but must be clearly identified.3.2.4 critical crack size Lin these test methods, thecrack size at which maximum force and catastrophic fractureoccur in the precracked beam (see Fig. 4) and the surface crackin flexure (see Fig. 5) configurations.
39、 In the chevron-notchedtest specimen (see Fig. 6) this is the crack size at which thestress intensity factor coefficient, Y*, is at a minimum orequivalently, the crack size at which the maximum force wouldoccur in a linear elastic, flat R-curve material.3.2.5 four-point -14 point flexureflexure conf
40、igurationwhere a beam test specimen is symmetrically loaded at twolocations that are situated one quarter of the overall span, awayfrom the outer two support bearings (see Fig. A1.1) (C 1161)3.2.6 fracture toughness KIpbFL-3/2the measured stressintensity factor corresponding to the extension resista
41、nce of astraight-through crack formed via bridge flexure of a sawnnotch or Vickers or Knoop indentation(s). The measurement isperformed according to the operational procedure herein andsatisfies all the validity requirements. (See Annex A2).NOTE 1Precracked beam test specimens are shown as examples.
42、 The small arrows denote the direction of crack growth.FIG. 1 Crack Plane Orientation Code for Hot-Pressed ProductsNOTE 1Precracked beam test specimens are shown as examples. The small arrows denote the direction of crack growth.FIG. 2 Crack Plane Orientation Code for Extruded ProductsC 1421 01b (20
43、07)33.2.7 fracture toughness KIscor KIsc*FL-3/2the mea-sured (KIsc) or apparent (KIsc*) stress intensity factor corre-sponding to the extension resistance of a semi-elliptical crackformed via Knoop indentation, for which the residual stressfield due to indentation has been removed. The measurement i
44、sperformed according to the operational procedure herein andsatisfies all the validity requirements. (See Annex A3).3.2.8 fracture toughness KIvbFL-3/2the measured stressintensity factor corresponding to the extension resistance of astably-extending crack in a chevron-notched test specimen.The measu
45、rement is performed according to the operationalprocedure herein and satisfies all the validity requirements.(See Annex A4).3.2.9 minimum stress-intensity factor coeffcient, Y*mintheminimum value of Y* determined from Y* as a function ofdimensionless crack length, a = a/W.3.2.10 pop-inin these test
46、methods, the sudden formationor extension of a crack without catastrophic fracture of the testNOTE 1The R/C mix shown in b) is a consequence of the parallel slicing of the test specimens from the product.NOTE 2Precracked beam test specimens are shown as examples. The small arrows denote the directio
47、n of crack growth.FIG. 3 Code for Crack Plane and Direction of Crack Extension in Test Specimens with Axial Primary Product DirectionFIG. 4 Cross Section of a pb Test Specimen Showing thePrecrack Configuration (a0.25,a0.50,a0.75are the Points for CrackLength Measurements)FIG.5aandbCrossSection of sc
48、 Test Specimens Showing thePrecrack Configurations for Two OrientationsC 1421 01b (2007)4specimen, apparent from a force drop in the applied force-displacement curve. Pop-in may be accompanied by an audiblesound or other acoustic energy emission.3.2.11 precracka crack that is intentionally introduce
49、dinto the test specimen prior to testing the test specimen tofracture.3.2.12 small cracka crack is defined as being small whenall physical dimensions (in particular, with length and depth ofa surface crack) are small in comparison to a relevant micro-structural scale, continuum mechanics scale, or physical sizescale. The specific physical dimensions that define “small”vary with the particular material, geometric configuration, andloadings of interest. (E 1823)3.2.13 stable crack extensioncontrollable, time-independent, noncritical
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