ASTM E399 is one of the most widely used fracture toughness tests across various industries. Known as the “Standard Test Method for Linear Elastic Fracture Toughness (K_Ic) of Metallic Materials,” it provides a precise method for measuring a material’s crack growth resistance. This article describes the standard, its test methods, and its applications.
What is ASTM E399?
Definition and main purpose
ASTM E399 – Standard Test Method for Linear Elastic Fracture Toughness (K_Ic) of Metallic Materials under Plane Stress. This specification applies to relatively brittle materials under plane stress.
What is K_Ic?
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A measure of a material’s ability to resist crack growth.
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Expressed in MPa√m.
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Intrinsic properties of the material (independent of the sample geometry)
Sampling requirements in ASTM E399
Types of acceptable samples:
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TC samples (Compressed Tension)
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SENB (Single Slotted Elbow) Example
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Example of DCB (double cantilever beam)
Sample size:
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Fish (b) must satisfy the level distortion condition.
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The initial crack length (A) is typically 0.45 to 0.55 times the specimen width (W).
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Minimum sample size: B ≥ 2.5(K_Ic/σ_y)²
Test method according to ASTM E399
1. Sample preparation
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Precise sample processing according to standard dimensions
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Crack formation is initiated mechanically or electrochemically.
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Pre-crack formation under cyclic loading
2. Installation of equipment
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Use high-precision tensile/flexural testing machines.
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Installation of an extensometer to measure the crack opening modulus (CMOD)
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Adjust the loading rate (usually 0.5–3 MPa√m/min).
3. Take the test
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Application of a constant and controlled load
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Recording load-displacement curves
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Stop the test after reducing the maximum load by 10%.
4. Analyze the results.
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Determine the critical load (P_Q) using the curve
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Calculate K_Q using the standard equation.
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Checking the results for compliance with standards
Criteria for verifying the results
To verify the K_Ic result, the following conditions must be met:
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Ratio P_max/P_Q ≤ 1.10
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Sample size ≥ 2.5(K_Q/σ_y)²
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The gap length should be between 0.45 W and 0.55 W after the test.
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Split angle ≤ 10°
Industrial Applications of ASTM E399
1. Aerospace industry
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Hardness determination of titanium and aluminum alloys
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Design of safe structures taking crack growth into account
2. Oil and gas industry
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Material selection for high-voltage devices
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Pipe life prediction
3. Power plant
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Assessment of steel hardness for steam boilers
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Monitoring material destruction by creep
4. Automotive industry
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Improvement of the body alloy
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Design of security systems
Advantages of using ASTM E399
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High accuracy : standard and repeatable method
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Reliability : the effective result of technical design
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Versatility : Can be used with various metal materials.
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Precise prognosis : The service life of the structure under load can be estimated.
Standard restrictions
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Only suitable for materials with relatively brittle behavior.
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Large samples are required for testing high-hardness materials .
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The testing costs are relatively high.
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Special equipment and trained operators are required.
Key points of the test
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High-quality sample processing is crucial.
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Pre-cuts should be made carefully.
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It is necessary to control the environmental conditions (temperature and humidity).
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Device calibration should be performed regularly.
Relevant rules
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ASTM E1820 : Nonlinear fracture toughness test
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ASTM E1921 : Test methods for testing ferritic steels at low temperatures
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ISO 12135 : similar international standard
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BS 7448 : British Standard for fracture toughness tests
Interpretation of test results
ASTM E399 test results help engineers:
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Calculate the minimum thickness required to prevent brittle fracture.
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Determine the maximum allowable crack size in the structure.
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Selection of materials for specific applications.
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Calculate the remaining service life of the cracked component.
Latest standard version
The latest revision of ASTM E399 was published in 2022 and includes the following significant changes:
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Update review criteria
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Added additional information on proactive methods.
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The most comprehensive guide to data analysis
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A new look at modern materials
Instructions for use for ACGL Accudraw glass cylinders from Primary Fluid Systems INC
Finally
ASTM E399 is an important tool for evaluating the safety and reliability of steel structures in various industries. Compliance with this standard enables engineers to create more precise designs and avoid catastrophic failures. A clear understanding and correct application of this standard is critical to ensuring product quality and structural integrity.
Accudraw Application Worksheet by Primary Fluid Systems INC
Frequently Asked Questions
1. What is the difference between ASTM E399 and ASTM E1820?
ASTM E399 applies to materials with linear elastic behavior, while ASTM E1820 applies to materials with nonlinear plastic behavior.
2. Why is it important to create pre-cracks in the sample?
The pre-cracking process simulates a more realistic physical defect state, making the results more reliable.
3. Does this standard also apply to non-metallic materials?
No, ASTM E399 is for metals. There are other standards for non-metallic materials, such as ASTM D5045 for plastics.
4. What is the minimum sample size required for testing?
To draw valid conclusions, at least three samples are usually required.
5. When should ASTM E399 be used?
When the ability of a material to resist crack growth under plane stress conditions needs to be evaluated, especially for brittle or semi-brittle materials.