ASTM E2472 Test to Determine Resistance of Metals to Stable Crack Extension

Scope:

ASTM E2472 test method is used to determine CTOA and COD of fatigue pre-cracked specimens that exhibit low constraint and that are tested under slowly increasing displacement. The test specimens tested are compact, and middle-crack-tension specimens.

This test method can be used:

• For research and development. 
• To determine how the changes in characteristics of metals can affect their resistance to stable cracks. Characteristics such as material thickness, material composition, thermo-mechanical processing, welding, and thermal stress relief are assessed.
• To establish specifications of acceptance and manufacturing quality control of base materials.
• To establish inspection and flaw assessment criteria in conjunction with fracture mechanics analyses. 
• To predict structural response and force-carrying capacity of cracked structural components.

Test Procedure:

In the ASTM E2472 method, tests are performed by applying slowly increasing displacements to the test specimen and measuring the forces, displacements, crack extension, and angles realized during the test. The forces, displacements, and angles are then used in conjunction with certain pre-test and post-test specimen measurements to determine the material’s resistance to stable crack extension. 

Four procedures that can be used for measuring crack extension are surface visual, unloading compliance, electrical potential, and multiple specimens. 

Two techniques that can be used for measuring CTOA are optical microscopy and digital image correlation.  

Three techniques that can be used for measuring COD are clip gauge, optical microscopy, and digital image correlation. 

Specimen size:

In ASTM E2472, to calculate the critical CTOA and COD resistance curve, the specimens must have a minimum width of 150 mm. The fatigue crack size from the notch front should be equal to or exceed the envelope. The fatigue crack extension, ∆a, should be equal to or greater than 0.5N, but not less than 2 mm in size.

Data:

For ASTM E2472, the crack-tip-opening angle (CTOA), ψ_c , and the crack opening displacement (COD), δ₅, resistance curves are presented. 

Conclusion:

ASTM E2472 test method is used to determine CTOA and COD of fatigue pre-cracked specimens that exhibit low constraint and that are tested under slowly increasing displacement.