1、Designation: C1368 10 (Reapproved 2017)C1368 18Standard Test Method forDetermination of Slow Crack Growth Parameters ofAdvanced Ceramics by Constant Stress-Rate Stress RateStrength Testing at Ambient Temperature1This standard is issued under the fixed designation C1368; the number immediately follow
2、ing the designation indicates the year oforiginal adoption or, in the 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. Scope*Scope1.1 This test me
3、thod covers the determination of slow crack growth (SCG) parameters of advanced ceramics by using constantstress-rate stress rate rectangular beam flexural testing, or ring-on-ring biaxial disk flexural testing, or direct tensile strength, inwhich strength is determined as a function of applied stre
4、ss rate in a given environment at ambient temperature. The strengthdegradation exhibited with decreasing applied stress rate in a specified environment is the basis of this test method which enablesthe evaluation of slow crack growth parameters of a material.NOTE 1This test method is frequently refe
5、rred to as “dynamic fatigue” testing (1-3)2 in which the term “fatigue” is used interchangeably with theterm “slow crack growth.” To avoid possible confusion with the “fatigue” phenomenon of a material which occurs exclusively under cyclic loading, asdefined in Terminology E1823, this test method us
6、es the term “constant stress-rate stress rate testing” rather than “dynamic fatigue” testing.NOTE 2In glass and ceramics technology, static tests of considerable duration are called “static fatigue” tests, a type of test designated as stress-rupturestress rupture (See Terminology E1823).1.2 Values e
7、xpressed in this test method are in accordance with the International System of Units (SI) and IEEE/ASTM SI 10.1.3 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 safe
8、ty safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Develo
9、pment of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3C1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient Temp
10、eratureC1239 Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced CeramicsC1273 Test Method for Tensile Strength of Monolithic Advanced Ceramics at Ambient TemperaturesC1322 Practice for Fractography and Characterization of Fracture Origins in Adv
11、anced CeramicsC1499 Test Method for Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient TemperatureE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE337 Test Method for Measuring Humidity with a Psychrometer (the Measu
12、rement of Wet- and Dry-Bulb Temperatures)E1823 Terminology Relating to Fatigue and Fracture TestingIEEE/ASTM SI 10 American National Standard for Use of the International System of Units (SI): The Modern Metric System3. Terminology3.1 Definitions:1 This test method is under the jurisdiction of ASTM
13、Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on MechanicalProperties and Performance.Current edition approved Feb. 1, 2017Jan. 1, 2018. Published February 2017January 2018. Originally approved in 1997. Last previous edition approved in 20102017 asC1368 1
14、0.C1368 10 (2017). DOI: 10.1520/C1368-10R17.10.1520/C1368-18.2 The boldface numbers in parentheses refer to the list of references at the end of this standard.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of A
15、STM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.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
16、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 ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standar
17、dCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.1 The terms described in Terminologies C1145, E6, and E1823 are applicable to this test method. Specific terms relevantto this test method are as follows:3.1.2 advanced ceramic, na
18、highly engineered, high-performance, predominately nonmetallic, inorganic, ceramic materialhaving specific functional attributes. (C1145)3.1.3 constant stress rate, , na constant rate of maximum stress applied to a specified beam by using either a constantloading or constant displacement rate of a t
19、esting machine.3.1.4 environment, nthe aggregate of chemical species and energy that surrounds a test specimen. (E1823)3.1.5 environmental chamber, nthe container of bulk volume surrounding a test specimen. (E1823)3.1.6 equibiaxial flexural strength, F/L2, nthe maximum stress that a material is capa
20、ble of sustaining when subjected toflexure between two concentric rings.3.1.6.1 DiscussionThis mode of flexure is a cupping of the circular plate caused by loading at the inner load ring and outer support ring. Theequibiaxial flexural strength is calculated from the maximum-load maximum load of a bi
21、axial test carried to rupture, the originaldimensions of the test specimen, and Poissons ratio. (C1499)3.1.7 flexural strength, f, FL2, na measure of the strength of a specified beam specimen in bending determined at a givenstress rate in a particular environment.3.1.8 fracture toughness, na generic
22、 term for measures of resistance to extension of a crack. (E1823)3.1.9 inert strength, FL2, na measure of the strength of a specified strength test specimen as determined in an appropriateinert condition whereby no slow crack growth occurs.3.1.9.1 DiscussionAn inert condition may be obtained by usin
23、g vacuum, low temperatures, very fast test rates, or any inert mediums.3.1.10 slow crack growth (SCG), nsubcritical crack growth (extension) which may result from, but is not restricted to, suchmechanisms as environmentally assisted stress corrosion or diffusive crack growth.3.1.11 strength-stress r
24、ate curve, na curve fitted to the values of strength at each of several stress rates, based on therelationship between strength and stress rate: log f = 1/(n + 1) log + log D. (See Appendix X1.)3.1.11.1 DiscussionIn the ceramics literature, this is often called a dynamic fatigue curve.3.1.12 strengt
25、h-stress rate diagram, na plot of strength against stress rate. Both strength and stress rate are plotted on log-logscales.3.1.13 stress intensity factor, KI, nthe magnitude of the ideal-crack-tip stress field (stress-field singularity) subjected to modeI loading in a homogeneous, linear elastic bod
26、y. (E1823)3.1.14 tensile strength strength, Su, F/L2, nStheuthe maximum tensile stress which a material is capable of sustaining.3.1.14.1 DiscussionTensile strength is calculated from the maximum force during a tension test carried to rupture and the original cross-sectional areaof the specimen. (C1
27、273)3.2 Definitions of Terms Specific to This Standard:3.2.1 slow crack growth parameters, n and D, nthe parameters estimated as constants in the flexural strength-stress rateequation, which represent the degree of slow crack growth susceptibility of a material. (See Appendix X1.)4. Significance and
28、 Use4.1 For many structural ceramic components in service, their use is often limited by lifetimes that are controlled by a processof SCG. This test method provides the empirical parameters for appraising the relative SCG susceptibility of ceramic materialsunder specified environments. Furthermore,
29、this test method may establish the influences of processing variables and compositionon SCG as well as on strength behavior of newly developed or existing materials, thus allowing tailoring and optimizing materialprocessing for further modification. In summary, this test method may be used for mater
30、ial development, quality control,C1368 182characterization, and limited design data generation purposes. The conventional analysis of constant stress-rate stress rate testingis based on a number of critical assumptions, the most important of which are listed in the next paragraphs.4.2 The flexural s
31、tress computation for the rectangular beam test specimens or the equibiaxial disk flexure test specimens isbased on simple beam theory, with the assumptions that the material is isotropic and homogeneous, the moduli of elasticity intension and compression are identical, and the material is linearly
32、elastic. The average grain size should be no greater thanone-fiftieth of the beam thickness.4.3 The test specimen sizes and fixtures for rectangular beam test specimens should be in accordance with Test Method C1161,which provides a balance between practical configurations and resulting errors, as d
33、iscussed in Refs (4, 5). Only four-point testconfiguration is allowed in this test method for rectangular beam specimens. Three-point test configurations are not permitted. Thetest specimen sizes and fixtures for disk test specimens tested in ring-on-ring flexure should be chosen in accordance with
34、TestMethod C1499. The test specimens for direct tension strength testing should be chosen in accordance with Test Method C1273.4.4 The SCG parameters (n and D) are determined by fitting the measured experimental data to a mathematical relationshipbetween strength and applied stress rate, log f = 1/(
35、n+1) log + log D. The basic underlying assumption on the derivation ofthis relationship is that SCG is governed by an empirical power-law crack velocity, v = AKI/KICn (see Appendix X1).NOTE 3There are various other forms of crack velocity laws which are usually more complex or less convenient mathem
36、atically, or both, but maybe physically more realistic (6). It is generally accepted that actual data cannot reliably distinguish between the various formulations. Therefore, themathematical analysis in this test method does not cover such alternative crack velocity formulations.4.5 The mathematical
37、 relationship between strength and stress rate was derived based on the assumption that the slow crackgrowth parameter is at least n 5 (1, 7, 8). Therefore, if a material exhibits a very high susceptibility to SCG, that is, n 2000 MPa/s) may remainunchanged so that a plateau is observed in the plot
38、of strength-versus-stress rate (7). If the strength data determined in this plateauregion are included in the analysis, a misleading estimate of the SCG parameters will be obtained. Therefore, the strength data inthe plateau shall be excluded as data points in estimating the SCG parameters of the ma
39、terial. This test method addresses for thisfactor by recommending that the highest stress rate be 2000 MPa/s.NOTE 5The strength plateau of a material can be checked by measuring an inert strength in an appropriate inert medium.NOTE 6When testing in environments with less than 100 % concentration of
40、the corrosive medium (for example, air), the use of stress rates greaterthan 1 MPa/s can result in significant errors in the slow crack growth parameters due to averaging of the regions of the slow crack growth curve (9).Such errors can be avoided by testing in 100%100 % concentration of the corrosi
41、ve medium (for example, in water instead of humid air). For the caseof 100 % concentration of the corrosive medium, stress rates as large as 2000 MPa/s may be acceptable.5.3 Surface preparation of test specimens can introduce fabrication flaws which may have pronounced effects on SCG behavior.Machin
42、ing damage imposed during specimen preparation can be either a random interfering factor or an inherent part of thestrength characteristics to be measured. Surface preparation can also lead to residual stress. Universal or standardized test methodsof surface preparation do not exist. It should be un
43、derstood that the final machining steps may or may not negate machining damageintroduced during the early coarse or intermediate machining steps. In some cases, specimens need to be tested in the as-processedcondition to simulate a specific service condition. Therefore, specimen fabrication history
44、may play an important role in slow crackgrowth as well as in strength behavior.6. Apparatus6.1 Testing MachineTesting machines used for this test method shall conform to the requirements of Practices E4. Specimensmay be loaded in any suitable testing machine provided that uniform test rates, either
45、using load-controlled or displacement-controlled mode, can be maintained. The loads used in determining strength shall be accurate to within 61.0 % at any load withinthe selected load rate and load range of the testing machine as defined in Practices E4. The testing machine shall have a minimumcapab
46、ility of applying at least four test rates with at least three orders of magnitude, ranging from 101 to 102 N/s forload-controlled mode and from 107 to 104 m/s for displacement-controlled mode.6.2 Test Fixtures, Four-Point Rectangular Beam FlexureThe configurations and mechanical properties of test
47、fixtures shouldbe in accordance with Test Method C1161. The materials from which the test fixtures including(including bearing cylinderscyl-inders) are fabricated shall be effectively inert to the test environment so that they do not react with or contaminate theenvironment.NOTE 7For testing in wate
48、r, for example, it is recommended that the test fixture be fabricated from stainless steel which is effectively inert to water.The bearing cylinders may be machined from hardenable stainless steel (for example, 440C grade) or a ceramic material such as silicon nitride, siliconcarbide, or alumina.6.2
49、.1 Four-Point FlexureThe four-point four-point-14-point fixture configuration as described in 6.2 of Test Method C1161shall be used in this test method. Three-point flexure is not permitted. The test fixtures shall be stiffer than the specimen, so thatmost of the crosshead or actuator travel is imposed onto the specimen.6.3 Test Fixtures, Equibiaxial Disk Flexural StrengthThe configurations and mechanical properties of test fixtures should bein accordance with Test Method C1499. The materials from which the test fixtu
