1、 Reference number ISO 24370:2005(E) ISO 2005INTERNATIONAL STANDARD ISO 24370 First edition 2005-06-01 Fine ceramics (advanced ceramics, advanced technical ceramics) Test method for fracture toughness of monolithic ceramics at room temperature by chevron-notched beam (CNB) method Cramiques techniques
2、 Mthode dessai de tnacit la rupture des cramiques monolithiques temprature ambiante sur prouvette entaille en chevron ISO 24370:2005(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited
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7、ublished in Switzerland ii ISO 2005 All rights reservedISO 24370:2005(E) ISO 2005 All rights reserved iiiContents Page Foreword iv 1 Scope 1 2 Normative references . 1 3 Terms and definitions. 1 4 Symbols . 2 5 Principle . 3 6 Apparatus. 3 6.1 Test machine . 3 6.2 Flexure fixtures . 3 6.3 Micrometer
8、. 4 6.4 Optical microscope. 4 6.5 Stability detection equipment 5 7 Test specimens . 5 7.1 Geometry, size, preparation and edge chamfering . 5 7.2 Number of specimens. 8 8 Procedure. 9 8.1 Permitted test environments 9 8.2 Test specimen dimensions and alignment. 9 8.3 Post-test measurements 10 8.4 P
9、ost-test interpretation. 10 9 Calculation. 12 9.1 Calculations of the minimum stress intensity factor coefficient Y* min . 12 9.2 Calculation of the fracture toughness value, K I,CNB . 13 10 Test report 13 Bibliography . 15 ISO 24370:2005(E) iv ISO 2005 All rights reservedForeword ISO (the Internati
10、onal Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been
11、 established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standa
12、rdization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for
13、voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all
14、such patent rights. ISO 24370 was prepared by Technical Committee ISO/TC 206, Fine ceramics. INTERNATIONAL STANDARD ISO 24370:2005(E) ISO 2005 All rights reserved 1Fine ceramics (advanced ceramics, advanced technical ceramics) Test method for fracture toughness of monolithic ceramics at room tempera
15、ture by chevron-notched beam (CNB) method 1 Scope This International Standard specifies a test method for determining the fracture toughness of monolithic ceramic materials at room temperature by the chevron-notched beam (CNB) method. This International Standard is applicable to monolithic ceramics
16、and whisker- or particulate-reinforced ceramics that are regarded as macroscopically homogeneous. It is not applicable to continuous-fibre reinforced ceramic composites. This International Standard is usually applicable to ceramic materials with a fracture toughness less than about 12 MPa(m 1/2 ). T
17、he test method is applicable to materials with a flat crack-growth resistance curve and may be applicable to materials with a rising crack-growth resistance curve (R-curve). 2 Normative references The following referenced documents are indispensable for the application of this document. For dated re
18、ferences, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 7500-1:2004, Metallic materials Verification of static uniaxial testing machines Part 1: Tension/compression testing machines Verification and calib
19、ration of the force-measuring system ISO 14704:2000, Fine ceramics (advanced ceramics, advanced technical ceramics) Test method for flexural strength of monolithic ceramics at room temperature 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 s
20、tress intensity factor K Imagnitude of the elastic stress field singularity at the tip of a crack subjected to opening mode (mode I) displacement NOTE It is a function of applied force and test specimen size, geometry and crack length. 3.2 fracture toughness generic term for measures of the resistan
21、ce of extension of a crack ISO 24370:2005(E) 2 ISO 2005 All rights reserved3.3 fracture toughness value K I,CNBvalue of crack-extension resistance, i.e. fracture toughness, as measured by the CNB method NOTE The measured stress intensity factor corresponds to a crack-extension resistance of a stably
22、-extending crack in a chevron-notched beam specimen. The measurement is performed to the operational procedure herein and satisfies all the validity requirements. NOTE The definition, interpretation and measurement of K I,CNBassume a flat crack-growth resistance curve. 3.4 critical stress intensity
23、factor K Iccritical value of K Iat which fracture occurs 4 Symbols l 0chevron tip dimension, CNB method (Figure 2) l 1chevron dimension, CNB method, l 1= (l 11+ l 12 )/2 l 11chevron dimension, CNB method (Figure 2) l 12chevron dimension, CNB method (Figure 2) B test specimen thickness (Figure 2) K I
24、stress intensity factor, Mode I K Iccritical stress intensity factor, Mode I K I,CNBfracture toughness value, chevron-notched beam method S oflexure fixture outer span S iflexure fixture inner span L test specimen length F maxmaximum force applied to the test specimen by the test machine and thereby
25、 recorded (Figure 5) F Tareforce applied to the test specimen by the upper fixture F total force applied to the test specimen (F max+ F Tare ). This value is used in calculation of K I,CNBT notch thickness or kerf resulting from cutting of the chevron notch (Figure 2) W test specimen width (Figure 2
26、) Y* minminimum value of the stress intensity factor coefficient Y* ISO 24370:2005(E) ISO 2005 All rights reserved 35 Principle This International Standard is intended to be used for material development, material comparison, quality assurance, characterization, reliability analysis and design data
27、generation. The chevron-notched beam (CNB) method measures the fracture toughness value K I,CNBby fracturing a flexural specimen, that has a chevron notch (Figures 1 and 2). The specimen is fractured by four-point flexure. Force versus displacement, and backface strain or time are recorded in order
28、to detect unstable fracture. The fracture toughness value K I,CNBis calculated from the fracture load and the minimum stress intensity factor coefficient. Background information concerning this test method may be found in References 1 and 2. An international interlaboratory comparison study (round r
29、obin) project on the chevron-notched method is described in Reference 3, and a comparison of this method to other standardized methods is given in References 2 and 4. NOTE Ceramics generally exhibit stable crack extension from a chevron notch if the notch is sufficiently narrow ( 0,30 mm), and the o
30、ther notch dimensions are within the specified tolerances. If stable crack extension is not obtained, then the fracture toughness cannot be directly measured. 6 Apparatus 6.1 Test machine A suitable testing machine capable of applying a uniform cross-head speed shall be used. The testing machine sha
31、ll be in accordance with ISO 7500-1:2004 Class 1, with an accuracy of 1 % of the indicated force at fracture. 6.2 Flexure fixtures A schematic diagramme of a typical flexure fixture and test specimen is shown in Figure 1. Flexure fixtures shall meet the requirements of ISO 14704. The fixtures should
32、 be semi-articulating. Test specimens shall be contacted by smooth cylindrical bearings with a diameter between 4,50 mm and 5,00 mm. The diameter should be uniform to 0,015 mm. The bearings shall be free to roll in order to minimize friction, and the two inner bearings shall be free to roll inward,
33、and the two outer bearings shall be free to roll outward. The inner span, S i , should measure 20 mm 0,5 mm and the outer span, S o , should measure 40 mm 0,5 mm. Alternatively, the inner and outer span may measure 10 mm and 30 mm, respectively. When specific test environments other than the laborat
34、ory air are employed, an adequate chamber to hold the environment around the test fixture is required. For gaseous environments such as dry nitrogen, a polyethylene bag can be used. For liquid environments such as silicone oil or water, the specimen can be coated and placed in the fixture or the fix
35、ture and test specimen can be immersed in a chamber containing the liquid. ISO 24370:2005(E) 4 ISO 2005 All rights reservedKey 1 push rod 2 ball 3 test specimen 4 strain gauge 5 displacement transducer 6 support rod 7 flexure fixture inner span, S i8 flexure fixture outer span, S oFigure 1 Schematic
36、 example of four-point flexure of a chevron-notched test specimen 6.3 Micrometer A micrometer such as shown in ISO 3611 11but with a resolution of 0,002 mm shall be used to measure the test specimen dimensions. The micrometer shall have flat anvil faces such as shown in ISO 3611 11 . The micrometer
37、shall not have a ball tip or sharp tip since these might damage the specimen. Alternative dimension-measuring instruments may be used provided that they have a resolution of 0,002 mm or finer. 6.4 Optical microscope A travelling microscope or an optical microscope equipped with a calibrated filar ey
38、epiece should be used to measure chevron notch dimensions l 0 , l 11 , l 12and T. Magnifications of 10 to 50 are usually required. The dimensional measurement performance of the measurement system shall be calibrated with a reference standard. ISO 24370:2005(E) ISO 2005 All rights reserved 56.5 Stab
39、ility detection equipment The stability of the test is detected by monitoring the test specimen centre-point displacement, load-point displacement, actuator displacement, cross-head displacement or backface strain. Alternatively, force can be recorded as a function of time. Examples of force as a fu
40、nction of strain, actuator stroke and time are shown in Figure 3. Both backface strain and extensometers placed within or near the flexure fixture are excellent for detecting the stability of the test 5 6 7 . Test system extensometers that are placed remotely relative to the test specimen are less s
41、ensitive to the local events in the test specimen and may not detect stable extension. Monitoring force as a function of time is a less effective method of detecting stable crack extension. This is particularly the case for materials with a low fracture toughness e.g. 3,0 MPa(m 1/2 ) and high elasti
42、c modulus (e.g. 400 GPa). Reference 2 discusses experience with various monitoring methods. If an extensometer contacting the test specimen is used, the force of the extensometer on the specimen should be less than 0,2 N. 7 Test specimens 7.1 Geometry, size, preparation and edge chamfering 7.1.1 Rec
43、ommended geometry Rectangular beams with dimensions shown in Figure 2 should be used. Cross-sectional tolerances should be 0,20 mm. The parallelism tolerance on opposite longitudinal faces should be 0,015 mm. The test specimen illustrated in Figure 2 resulted in excellent correlation to other standa
44、rdized test methods for a wide variety of ceramics 2 , and has been used in the development of a reference material 4 . The stress intensity factor coefficient is based on the straight-through-crack-assumption model and correlates well with finite element analysis (FEA) models for the range allowed2
45、 . ISO 24370:2005(E) 6 ISO 2005 All rights reservedDimension in millimetres Key L test specimen length, min. 45 L/2 22,5 0,50 B test specimen thickness, 3,00 0,20 W test specimen width, 4,00 0,20 l 0chevron tip dimension, CNB method, 0,80 0,08 l 11chevron dimension, CNB method, min. 3,80, max. W; no
46、 overcut l 12chevron dimension, CNB method, min. 3,80, max. W; no overcut T notch thickness or kerf, max. 0,30 Do not bevel edges. Notch planes should meet within 0,06 mm. aNotch tip detail. bChevron tip on centreline within 0,06 mm. Figure 2 Test specimen configuration and terminology for the recom
47、mended geometry ISO 24370:2005(E) ISO 2005 All rights reserved 7a) Force as a function of strain b) Force as a function of actuator stroke c) Force as a function of time Key X 1back-face strain (10 6 ) X 2actuator stroke, millimetres t time, seconds F force, newtons NOTE 1 A 20 Hz data acquisition r
48、ate was used. NOTE 2 Test material was alpha silicon carbide. Figure 3 Examples of force as a function of strain, actuator stroke and time ISO 24370:2005(E) 8 ISO 2005 All rights reserved7.1.2 Alternative geometry In some instances, circumstances such as availability of test material, existing test
49、configurations, machining capability, or other considerations may dictate a choice of test specimen geometry and/or dimensions other than those recommended in 7.1.1. In those instances, alternative geometries and basic dimensions (e.g. L, W, B) can generally be employed with the following guidelines. Basic dimensions and tolerances should be proportional to those recommended. In addition, values of 1= l 1 /W and 0= l 0 /W should be chosen to be in the r
