Measurement of Initiation Toughness in Surface Cracks ASTM E2899

Measurement of Initiation Toughness in Surface Cracks ASTM E2899

ASTM E2899 test method deals with the measurement of toughness in fatigue sharpened, semi-elliptical surface cracks under tension and bending. This method is used to detect the initiation of crack extension in detail under specific conditions and applies to homogeneous metallic materials that are stress-free. SI units are considered to be standard.

    Scope:

    ASTM E2899 test method defines a standard for test and analysis of surface cracks that aids in research and helps explain test specimens in three regimes: an elastic-plastic regime, a linear-elastic regime, and a field-collapse regime. It provides details about the design, crack-front behavior, and toughness of the material, making it applicable for use. Electric potential, crack mouth opening displacement, acoustic emissions are detected in this method. 

    Procedure:

    Fracture toughness is calculated as a function of toughness and constraint value. The testing apparatus comprises notches and fatigue sharpening surface cracks with the specimens that show the tearing upon applying tension or bending force. The characteristics of the specimen are carefully measured, and testing is initiated under displacement control. Mechanical alignment is used to deal with non-uniformity. A bend testing fixture is installed, and the tension is applied to the specimen. The region of crack is observed and compared with material properties.

    Specimen size

    The specimen size should be as per requirements, with the weight and length measurements taken as follows:

     W ≥ 5 × 2 c and L ≥ 2W.

    Here, c= surface crack length

    Data:

    A toughness-constraint locus is created by comparing Kφ or Jφ to the values obtained in the variable constraints of specimens.
    Calculate Kφ with the specimen dimensions, crack dimensions, initiation force (Pi) or moment (Mi), and the initiation angle (φi) using the appropriate equations.

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