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    ASTM E399 - 20a

    Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials

    Active Standard ASTM E399 | Developed by Subcommittee: E08.07

    Book of Standards Volume: 03.01

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    Significance and Use

    5.1 The property KIc determined by this test method characterizes the resistance of a material to fracture in a neutral environment in the presence of a sharp crack under essentially linear-elastic stress and severe tensile constraint, such that (1) the state of stress near the crack front approaches tritensile plane strain, and (2) the crack-tip plastic zone is small compared to the crack size, specimen thickness, and ligament ahead of the crack.

    5.1.1 Variation in the value of KIc can be expected within the allowable range of specimen proportions, a/W and W/B. KIc may also be expected to rise with increasing ligament size. Notwithstanding these variations, however, KIc is believed to represent a lower limiting value of fracture toughness (for 2 % apparent crack extension) in the environment and at the speed and temperature of the test.

    5.1.2 Lower values of KIc can be obtained for materials that fail by cleavage fracture; for example, ferritic steels in the ductile-to-brittle transition region or below, where the crack front length affects the measurement in a stochastic manner independent of crack front constraint. The present test method does not apply to such materials and the user is referred to Test Method E1921 and E1820. Likewise this test method does not apply to high toughness or high tearing-resistance materials whose failure is accompanied by appreciable amounts of plasticity. Guidance on testing elastic-plastic materials is given in Test Method E1820.

    5.1.3 The value of KIc obtained by this test method may be used to estimate the relation between failure stress and crack size for a material in service wherein the conditions of high constraint described above would be expected. Background information concerning the basis for development of this test method in terms of linear elastic fracture mechanics may be found in Refs (1) and (2).

    5.1.4 Cyclic forces can cause crack extension at KI values less than KIc. Crack extension under cyclic or sustained forces (as by stress corrosion cracking or creep crack growth) can be influenced by temperature and environment. Therefore, when KIc is applied to the design of service components, differences between laboratory test and field conditions shall be considered.

    5.1.5 Plane-strain fracture toughness testing is unusual in that there can be no advance assurance that a valid KIc will be determined in a particular test. Therefore, compliance with the specified validity criteria of this test method is essential.

    5.1.6 Residual stresses can adversely affect the indicated KQ and KIc values. The effect can be especially significant for specimens removed from as-heat treated or otherwise non-stress relieved stock, from weldments, from complex wrought parts, or from parts with intentionally induced residual stresses. Indications of residual stress include distortion during specimen machining, results that are specimen configuration dependent, and irregular fatigue precrack growth (either excessive crack front curvature or out-of-plane growth). Guide B909 provides supplementary guidelines for plane strain fracture toughness testing of aluminum alloy products for which complete stress relief is not practicable. Guide B909 includes additional guidelines for recognizing when residual stresses may be significantly biasing test results, methods for minimizing the effects of residual stress during testing, and guidelines for correction and interpretation of data.

    5.2 This test method can serve the following purposes:

    5.2.1 In research and development, to establish in quantitative terms significant to service performance, the effects of metallurgical variables such as composition or heat treatment, or of fabricating operations such as welding or forming, on the fracture toughness of new or existing materials.

    5.2.2 In service evaluation, to establish the suitability of a material for a specific application for which the stress conditions are prescribed and for which maximum flaw sizes can be established with confidence.

    FIG. 2 Double–Cantilever Clip-In Displacement Gage Showing Mounting by Means of Integral Knife Edges
    (Gage Design Details are Given in Annex A1)

     Double–Cantilever Clip-In Displacement Gage Showing Mounting by Means of Integral Knife Edges(Gage Design Details are Given in ) Double–Cantilever Clip-In Displacement Gage Showing Mounting by Means of Integral Knife Edges(Gage Design Details are Given in )

    5.2.3 For specifications of acceptance and manufacturing quality control, but only when there is a sound basis for specifying minimum KIc values, and then only if the dimensions of the product are sufficient to provide specimens of the size required for valid KIc determination. The specification of KIc values in relation to a particular application should signify that a fracture control study has been conducted for the component in relation to the expected loading and environment, and in relation to the sensitivity and reliability of the crack detection procedures that are to be applied prior to service and subsequently during the anticipated life.


    1. Scope

    1.1 This test method covers the determination of fracture toughness (KIc and optionally KIsi) of metallic materials under predominantly linear-elastic, plane-strain conditions using fatigue precracked specimens having a thickness of 1.6 mm (0.063 in.) or greater2 subjected to slowly, or in special (elective) cases rapidly, increasing crack-displacement force. Details of test apparatus, specimen configuration, and experimental procedure are given in the annexes. Two procedures are outlined for using the experimental data to calculate fracture toughness values:

    1.1.1 The KIc test procedure is described in the main body of this test standard and is a mandatory part of the testing and results reporting procedure for this test method. The KIc test procedure is based on crack growth of up to 2 % percent of the specimen width. This can lead to a specimen size dependent rising fracture toughness resistance curve, with larger specimens producing higher fracture toughness results.

    1.1.2 The KIsi test procedure is described in Appendix X1 and is an optional part of this test method. The KIsi test procedure is based on a fixed amount of crack extension of 0.5 mm, and as a result, KIsi is less sensitive to specimen size than KIc. This less size-sensitive fracture toughness, KIsi, is called size-insensitive throughout this test method. Appendix X1 contains an optional procedure for reinterpreting the force-displacement test record recorded as part of this test method to calculate the additional fracture toughness value, KIsi.

    Note 1: Plane-strain fracture toughness tests of materials thinner than 1.6 mm (0.063 in.) that are sufficiently brittle (see 7.1) can be made using other types of specimens (1).3 There is no standard test method for such thin materials.

    1.2 This test method is divided into two parts. The first part gives general recommendations and requirements for testing and includes specific requirements for the KIc test procedure. The second part consists of Annexes that give specific information on displacement gage and loading fixture design, special requirements for individual specimen configurations, and detailed procedures for fatigue precracking. Additional annexes are provided that give specific procedures for beryllium and rapid-force testing, and the KIsi test procedure, which provides an optional additional analysis procedure for the test data collected as part of the KIc test procedure.

    1.3 General information and requirements common to all specimen configurations:



    Referenced Documents




     Stress-Intensity Factor


     Plane-Strain Fracture Toughness


     Crack Plane Orientation


    Summary of Test Method


    Significance and Use





    5.1.1 – 5.1.5

     Practical Applications


    Apparatus (see also 1.4)


     Tension Machine


     Fatigue Machine


     Loading Fixtures


     Displacement Gage, Measurement


    Specimen Size, Configurations, and Preparation (see also 1.5)


     Specimen Size Estimates


     Standard and Alternative Specimen Configurations


     Fatigue Crack Starter Notches


     Fatigue Precracking (see also 1.6)


     Crack Extension Beyond Starter Notch

    General Procedure


     Specimen Measurements






      Crack Size


      Crack Plane Angle


     Specimen Testing


      Loading Rate


      Test Record


    Calculation and Interpretation of Results


     Test Record Analysis


    Pmax/PQ Validity Requirement


     Specimen Size Validity Requirements




    Precision and Bias


    1.4 Specific requirements related to test apparatus:

    Double-Cantilever Displacement Gage

    Annex A1

    Testing Fixtures

    Annex A2

    Bend Specimen Loading Fixture

    Annex A2.1

    Compact Specimen Loading Clevis

    Annex A2.2

    1.5 Specific requirements related to individual specimen configurations:

    Bend Specimen SE(B)

    Annex A3

    Compact Specimen C(T)

    Annex A4

    Disk-Shaped Compact Specimen DC(T)

    Annex A5

    Arc-Shaped Tension Specimen A(T)

    Annex A6

    Arc-Shaped Bend Specimen A(B)

    Annex A7

    1.6 Specific requirements related to special test procedures:

    Fatigue Precracking KIc and KIsi Specimens

    Annex A8

    Hot-Pressed Beryllium Testing

    Annex A9

    Rapid-Force Testing

    Annex A10

    Determination of KIsi

    Appendix X1

    1.7 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

    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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

    1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

    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

    B645 Practice for Linear-Elastic Plane-Strain Fracture Toughness Testing of Aluminum Alloys

    B909 Guide for Plane Strain Fracture Toughness Testing of Non-Stress Relieved Aluminum Products

    E4 Practices for Force Verification of Testing Machines

    E8/E8M Test Methods for Tension Testing of Metallic Materials

    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)

    E456 Terminology Relating to Quality and Statistics

    E647 Test Method for Measurement of Fatigue Crack Growth Rates

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

    E1820 Test Method for Measurement of Fracture Toughness

    E1823 Terminology Relating to Fatigue and Fracture Testing

    E1921 Test Method for Determination of Reference Temperature, To, for Ferritic Steels in the Transition Range

    E1942 Guide for Evaluating Data Acquisition Systems Used in Cyclic Fatigue and Fracture Mechanics Testing

    E3076 Practice for Determination of the Slope in the Linear Region of a Test Record

    ICS Code

    ICS Number Code 77.040.10 (Mechanical testing of metals)

    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/E0399-20A

    Citation Format

    ASTM E399-20a, Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials, ASTM International, West Conshohocken, PA, 2020, www.astm.org

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