ASTM C1421 - 16

    Standard Test Methods for Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperature

    Active Standard ASTM C1421 | Developed by Subcommittee: C28.01

    Book of Standards Volume: 15.01

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    Significance and Use

    5.1 Fracture toughness, KIc, is a measure of the resistance to crack extension in a brittle material. These test methods may be used for material development, material comparison, quality assessment, and characterization.

    5.2 The pb and the vb fracture toughness values provide information on the fracture resistance of advanced ceramics containing large sharp cracks, while the sc fracture toughness value provides this information for small cracks comparable in size to natural fracture sources. Cracks of different sizes may be used for the sc method. If the fracture toughness values vary as a function of the crack size it can be expected that KIsc will differ from KIpb and KIvb. Table 1 tabulates advantages, disadvantages, and applicability of each method.

    1. Scope

    1.1 These test methods cover the fracture toughness, KIc, determination of advanced ceramics at ambient temperature. The methods determine KIpb (precracked beam test specimen), KIsc (surface crack in flexure), and KIvb (chevron-notched beam test specimen). The fracture toughness values are determined using beam test specimens with a sharp crack. The crack is either a straight-through crack formed via bridge flexure (pb), or a semi-elliptical surface crack formed via Knoop indentation (sc), or it is formed and propagated in a chevron notch (vb), as shown in Fig. 1.

    Note 1: The figures on the right show the test specimen cross sections and crack types. Four-point loading may be used with all three methods. Three-point may be used with the pb and vb specimens.

    Note 1: The terms bend(ing) and flexure are synonymous in these test methods.

    1.2 These test methods are applicable to materials with either flat or with rising R-curves. Differences in test procedure and analysis may cause the values from each test method to be different. For many materials, such as the silicon nitride Standard Reference Material 2100, the three methods give identical results at room temperature in ambient air.

    1.3 The fracture toughness values for a material can be functions of environment, test rate and temperature. These test methods give 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 are macroscopically homogeneous and microstructurally 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 general. It is followed by annexes and appendices with specific information for the particular test methods.

    Main Body




     Referenced Documents


     Terminology (including definitions, orientation and symbols)


     Summary of Test Methods


     Significance and Use






     Test Specimen Configurations, Dimensions and Preparations


     General Procedures


     Report (including reporting tables)


     Precision and Bias




     Summary of Changes




     Test Fixture Geometries

    Annex A1

     Procedures and Special Requirements for Precracked Beam Method

    Annex A2

     Procedures and Special Requirements for Surface Crack in Flexure Method

    Annex A3

     Procedures and Special Requirements for Chevron Notch Flexure Method

    Annex A4



     Precrack Characterization, Surface Crack in Flexure Method

    Appendix X1

     Complications in Interpreting Surface Crack in Flexure Precracks

    Appendix X2

     Alternative Precracking Procedure, Surface Crack in Flexure Method

    Appendix X3

    Chamfer Correction Factors, Surface Crack in Flexure Method Only

    Appendix X4

    Crack Orientation

    Appendix X5

    1.6 Values expressed in these test methods are in accordance with the International System of Units (SI) and Practice IEEE/ASTM SI 10.

    1.7 The values stated in SI units are to be regarded as standard. 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 responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    C1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature

    C1322 Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics

    E4 Practices for Force Verification of Testing Machines

    E112 Test Methods for Determining Average Grain Size

    E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods

    E337 Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)

    E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

    E740 Practice for Fracture Testing with Surface-Crack Tension Specimens

    E1823 Terminology Relating to Fatigue and Fracture Testing

    Reference Material

    NIST SRM 2100 Fracture Toughness of Ceramics Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070,

    ICS Code

    ICS Number Code 81.060.30 (Advanced ceramics)

    UNSPSC Code

    UNSPSC Code

    Referencing This Standard
    Link Here
    Link to Active (This link will always route to the current Active version of the standard.)

    DOI: 10.1520/C1421-16

    Citation Format

    ASTM C1421-16, Standard Test Methods for Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperature, ASTM International, West Conshohocken, PA, 2016,

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