ASTM E1820 Standard Test Method for Measurement of Fracture Toughness

Scope:

ASTM E1820 method is used to measure fracture toughness. Fracture toughness describes the resistance of metals to the propagation of flaws under applied stress, and it assumes that the longer the crack, the lower is the stress needed to cause a fracture. The ability of a crack to cause fracture depends on the fracture toughness of the material. Fracture toughness can be used for material comparison, selection, and quality assurance. It can also be used to rank materials within a similar yield strength range. Fracture toughness can be used to assess structural flaw tolerance. To make a proper flaw tolerance assessment, differences between laboratory tests and field conditions are kept in mind. 

Test Procedure:

In ASTM E1820 test method, a pre-cracked specimen is loaded to induce (1) unstable crack extension, referred to as fracture instability, (2) and stable crack extension, referred to as stable tearing. Unstable crack extension results in a single point-value of fracture toughness determined at the point of instability, and stable crack extension results in a continuous fracture toughness versus crack-extension relationship (R-curve) from which significant point-values may be determined. 

Video 01: Method to measure fracture toughness

Specimen size:

In ASTM E1820, all specimens should contain notches that are sharpened with fatigue cracks. They should be single-edge bend, compact, and disk-shaped compact. The dimension of the specimen varies with the test method applied. 

Data:

To substantiate the validity of a KIc determination in ASTM E1820 testing, first, a conditional result, K_Q, is calculated which involves construction on the test record.

A provisional toughness K_Q is given as:

Fracture Toughness of Metals: 

Conclusion:

ASTM E1820 method is used to measure fracture toughness. Fracture toughness describes the resistance of metals to the propagation of flaws under applied stress, and it assumes that the longer the crack, the lower is the stress needed to cause a fracture.