ASTM E1921 Determination of Reference Temperature for Ferritic Steels

Scope:

ASTM E1921 test method defines a standard for the choice of the specimen based on proportional dimensions and is unique to homogeneous materials. It deals with cleavage cracking and temperature changes. It determines the fracture toughness and tolerance of ferritic steels. This method deals with screening criterion, theoretical reasoning, and shape-location master curve determination of the specimen. Measures are taken for the smooth application of specimens and for enhancing their reliability and assessment.

Procedure:

In ASTM E1921, the specimens such as notched and fatigue pre-cracked bends or compact specimens are tested at a specific temperature. An autographic recorder detects the force and displacement changes, and the fracture toughness is measured. A partial unloading compliance method measures the crack growth, and an appropriate temperature for the test is selected. Welding or spot welding each thermocouple wire to the specimen helps record the test temperature. The estimated crack size slope is compared against the defined pre-crack size, and modulus adjustments are made. All the data is recorded under displacement control, and reference temperature is obtained.

Specimen size:

For ASTM E1921, the specimen size should be as per the requirements. For initial crack size a_o about 0.5W ± 0.05W, specimen width shall be 2B.

Data:

The following equation can be used in ASTM E1921 testing to calculate the value of reference temperature T_o that is adjusted for the detected uncertainty:

T_omar ꞊ T_o + σ (Z_y)

Where: T_omar = Margin adjusted T_o value

σ = standard deviation of T_o
Zy = Z-score at a specified confidence level (y)

Conclusion:

ASTM E1921 test method defines a standard for the choice of the specimen based on proportional dimensions and is unique to homogeneous materials.