ASTM E399 Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness of Metallic Materials

Get Certified ASTM E399 Testing for Reliable Fracture Toughness Evaluation 

ASTM E399 testing is a standardized method for measuring the fracture toughness of metallic materials under plane-strain, predominantly linear-elastic conditions. Skilled personnel prepare fatigue precracked specimens, and fracture testing is performed under controlled fracture testing conditions with appropriate loading and displacement measurement equipment. The test assesses whether the fracture response measured meets the necessary validity criteria for reporting Kᵢc. To achieve reliable results, specimen dimensions, crack-preparation procedures, loading rate, measurement accuracy, and correct interpretation of the test record are important.

The scope of ASTM E399 includes:

• Material: Material for which plane-strain fracture conditions are predominantly linear-elastic. 
• Objective: Determine the resistance of a metallic material to fracture in the presence of a sharp fatigue precrack and high tensile constraint. 
• Property measurement: Primarily plane-strain fracture toughness Kᵢc, with an optional determination of Kᵢsi under the procedure provided in Appendix X1. 
• Method: Fatigue-precracked specimens are loaded with a controlled crack-displacement force, and the load, displacement, specimen dimensions, and crack characteristics are measured. 
• Result: A valid Kᵢc can be used to describe fracture resistance under the extreme constraint conditions imposed by the test and, if applicable, to aid fracture-control evaluations. 
• Limitations of the test: The method does not apply to materials with significant plastic deformation during fracture.
• Environmental conditions: Kᵢc represents fracture resistance under the environment, test temperature, and loading conditions used during the laboratory test; differences between laboratory and service conditions should be considered. 
• Applications: Materials research and development, service evaluation, fracture-control studies, acceptance specifications, and manufacturing quality control if the validity and product-size conditions are met.

What are the uses of ASTM E399 testing? 

ASTM E399 testing is employed when engineers and materials laboratories require a standardized measure of the resistance of metals to fracture under linear-elastic, plane-strain conditions. The data obtained can be used to describe the effects of material composition, heat treatment, fabrication processes, and other metallurgical parameters on fracture behavior. This standard-

• Determines the fracture toughness of severely tensile constrained metallic materials. 
• Supports research into the effects of composition, heat treatment, welding, forming, and other processing variables. 
• Supplies fracture toughness data for service evaluations if the stresses present and maximum acceptable flaw tolerances are known. 
• Supports fracture-control studies for metallic components and structures. 
• May be used for acceptance or manufacturing quality control when a technically justified minimum Kᵢc value is specified. 
• Provides an optional Kᵢsi analysis that can offer a less specimen-size-sensitive fracture toughness value under the conditions defined by the standard.

Which Materials Can Be Tested Under ASTM E399? 

ASTM E399 applies to metallic materials that can be analyzed under essentially plane-strain, linear-elastic conditions. The material should be able to yield a specimen of suitable shape and size for a proper fracture toughness measurement.

Why is ASTM E399 important? 

ASTM E399 offers a controlled technique to measure the fracture resistance of metals under high constraint conditions. The Kᵢc property can be used to relate material fracture resistance to the relationship between applied stress and crack size when the service conditions reasonably resemble the high-constraint conditions represented by the test.

ASTM E399 Testing Process and Data Collection 

In ASTM E399, a metallic specimen is precracked in a fatigue crack, and then the force to displace the crack is increased. Technicians record the dimensions and characteristics of the crack in the specimen before testing and record the force-displacement response throughout the fracture loading. The resulting test record is then analyzed for the appropriate fracture-toughness parameters. Analysts then evaluate the required load relationships and specimen-size criteria to establish whether a valid Kᵢc value has been obtained. Where selected, the same test record can also be evaluated using the optional Kᵢsi procedure.

Common Challenges and Troubleshooting 

The accuracy of ASTM E399 results relies on accurate specimen machining, fatigue precracking, crack measurement, stable loading, and correct measurement of displacement. Residual stresses can bias Kᵢc and KQ determinations, particularly in material taken from heat-treated stock, weldments, complex wrought products, rapidly solidified castings, additively manufactured products, or products with intentionally induced residual stresses. Technicians should also monitor crack-front condition and specimen configuration because irregular fatigue-precrack growth or specimen-dependent behavior can indicate problems affecting the validity of the result.

Link to ASTM E399