Determination of Reference Temperature for Ferritic Steels ASTM E1921

Determination of Reference Temperature for Ferritic Steels ASTM E1921

The ASTM E1912 test method determines the characteristics of toughness and cleavage cracking at ferritic steels' elastic or elastic-plastic state by measuring the reference temperature. The fatigue precracked single-edge notched bars, and disk-shaped compact tension specimens with yield strength ranging from 275 to 825 MPa are used for the test after relieving the stress.

    Scope:

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

    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 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

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

    Data:

    The following equation can be used to calculate the value of reference temperature To that is adjusted for the detected uncertainty:

    Tomar ꞊ To + σ (Zy)

    Where: Tomar ꞊ = Margin adjusted To value

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

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