GB/T 21143-2025 Metallic materials - Unified method of test for determination of quasistatic fracture toughness English, Anglais, Englisch, Inglés, えいご
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ICS 13.220.10
CCS H 57
National Standard of the People's Republic of China
GB/T 21143-2025
Metallic materials - Unified method of test for determination of quasistatic fracture toughness
金属材料 准静态断裂韧度的统一试验方法
Issue date: 2025-10-31 Implementation date: 2026-05-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
4 Symbols and Descriptions
5 General Requirements
6 Determination of Fracture Toughness Under Stable and Unstable Crack
Bibliography
1 Scope
This document describes test methods for determining the fracture toughness and resistance curves of homogeneous metallic materials in terms of K, δ, and J under quasi-static loading conditions. The specimens contain notches, with pre-cracks introduced by fatigue, and tests are conducted under conditions of slowly increasing displacement. Fracture toughness is determined from the state of independent specimens at or after events such as ductile crack extension, instability of ductile crack extension, or unstable crack propagation. When crack extension manifests as stable growth under ductile tearing conditions, a resistance curve representing the relationship between fracture toughness and the amount of crack extension can be determined. For some ferritic materials, unstable crack propagation due to cleavage may occur during testing, or the initiation and growth of ductile cracks may be interrupted by cleavage propagation. Crack constraint conditions are not addressed within the scope of this document. GB/T 28896 supplements specific test requirements and data processing procedures for welded materials.
Note: Statistical variation in test results is related to fracture type. For example, fracture toughness values obtained from cleavage fracture of ferritic steels can fluctuate. For situations requiring high reliability, Reference [4] provides treatment methods for quantitatively characterizing the fluctuation of fracture toughness values in the ductile-to-brittle transition region. This document does not provide further elaboration on the number of tests or the application and interpretation of test results under such circumstances.*
2 Normative References
The content of the following documents, through normative references in the text, constitutes indispensable provisions of this document. For dated references, only the edition corresponding to that date is applicable to this document; for undated references, the latest edition (including all amendments) is applicable.
GB/T 8170 Rules of rounding off for numerical values & expression and judgement of limiting values
GB/T 12160 Metallic materials — Calibration of extensometer systems used in uniaxial testing (GB/T 12160-2019, ISO 9513:2012, IDT)
GB/T 16825.1 Metallic materials — Calibration and verification of static uniaxial testing machines — Part 1: Tension/compression testing machines — Calibration and verification of the force-measuring system (GB/T 16825.1-2022, ISO 7500-1:2018, IDT)
GB/T 20832 Metallic materials — Designation of test specimen axes in relation to product texture (GB/T 20832-2007, ISO 3785:2006, IDT)
GB/T 28896 Metallic materials — Method of test for the determination of quasistatic fracture toughness of welded joints (GB/T 28896-2023, ISO 15653:2018, MOD)
JJG 762 Verification Regulation of Extensometers
3 Terms and Definitions
The following terms and definitions apply to this document.
3.1
stress intensity factor
K
A parameter characterizing the magnitude of the elastic stress field in a region near the crack tip of a homogeneous, linear-elastic body.
Note: The stress intensity factor is a function of applied force, specimen dimensions, geometry, and crack length.
3.2
crack-tip opening displacement
CTOD
δ
The displacement by which the two crack surfaces separate at the tip of the pre-existing fatigue crack, relative to the original undeformed crack plane, calculated using a rotation formula.
3.3
J-integral
J
A line or surface integral taken from one crack surface to the other around the crack front of a quasi-crack, used to characterize the stress-strain field in the region ahead of the crack tip.
3.4
J value
The experimental equivalent of the J-integral, a specific value determined by this test method (J₀, Jᵢ, etc.), representing the characteristic fracture toughness under elastic-plastic conditions.
3.5
stable crack extension
Under displacement-controlled test conditions, the amount of crack extension that stops or will stop when the displacement is held constant.
3.6
unstable crack extension
Unstable crack propagation, which may or may not be preceded by stable crack extension (3.5).
3.7
pop-in
A sudden discontinuity on the force-displacement record, typically manifested as a sudden increase in displacement accompanied by a drop in force followed by a recovery.
Note 1: The values of displacement and force may continue to increase after the pop-in event and may exceed the values before the pop-in.*
Note 2: When testing according to this document, unstable crack extension (3.6) in the plane of the pre-crack may cause pop-in. This needs to be distinguished from other phenomena such as: 1) delamination and tearing perpendicular to the crack plane; 2) slipping of support rollers in three-point bending tests or pin slip in the loading train of compact tension specimens; 3) improper installation of displacement extensometers; 4) crushing of ice on crack surfaces during low-temperature testing; 5) electronic interference in the force and displacement measurement and recording equipment, etc.*
3.8
crack extension resistance curve
R-curve
A curve showing the variation of δ or J with the amount of stable crack extension.
3.9
stretch zone
The plastically deformed region formed by blunting of the crack tip.
3.10
section
A longitudinal section of the specimen that is perpendicular to the crack plane and includes the crack.
4 Symbols and Descriptions
The symbols and descriptions listed in Table 1 apply to this document.
5 General Requirements
5.1 General
The fracture toughness of metallic materials can be characterized either as characteristic (single-point) values (see Chapter ...) or as continuous curves over a limited range of crack extension (see Chapter 7). The procedures and parameters used to determine fracture toughness vary depending on the degree of plasticity exhibited by the specimen during the test. The test procedure and parameters for determining material fracture toughness are selected based on a progressive understanding of the specimen's plasticity level during the testing process. However, under any given conditions, any of the fatigue pre-cracked specimen configurations specified in this method can be used to measure any of the fracture toughness parameters. The tests involve slowly increasing displacement on the specimen,
