STP1189

    Environmentally Controlled Fracture of an Overstrained A723 Steel Thick-Wall Cylinder

    Published: Jan 1993


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    Abstract

    A through-wall, 1.7-m-long crack grew suddenly from an outer diameter (OD) notch in a 285-mm-OD A723 steel overstrained tube that was undergoing plating operations with no externally applied loads. A description is given of the fracture mechanics tests and analyses and the fractography that were performed to characterize the cracking. Key material, residual stress, and environment information are: 1200 MPa yield strength; 150 MPa √m fracture toughness; composition typical of air-melt A723 steel; tensile residual stress at the OD of about 600 MPa; and electro-polishing bath of sulfuric and phosphoric acids at 54°C.

    The bolt-loaded test for threshold stress intensity factor for environmentally controlled cracking described by Wei and Novak was used here with two significant modifications. Some tests included only a notch with radius matching that of the tube, and a new expression for K in terms of crack-mouth displacement was developed and used. Scanning electron microscopy (SEM) fractography and energy dispersive X-ray spectra were used to identify cracking mechanisms.

    Results of the investigation include: (a) a measured threshold of hydrogen stress cracking for the material/environment below 20 MPa √m, (b) da/dt versus K behavior typical of classic environmental control, (c) an improved K/v expression for the bolt-loaded specimen and associated criteria for determining plane strain test conditions in relation to the Irwin plastic zone.

    Keywords:

    environmental cracking, test methods, hydrogen stress cracking, thick-wall cylinder, K, analysis, scanning electron microscopy, residual stress, fracture mechanics, fatigue (materials)


    Author Information:

    Underwood, JH
    Materials engineer, mechanical engineer, chemical engineer, physical science technician, and metallurgist, Army Armament RD&E Center, Benet Laboratories, Watervliet, NY

    Olmstead, VJ
    Materials engineer, mechanical engineer, chemical engineer, physical science technician, and metallurgist, Army Armament RD&E Center, Benet Laboratories, Watervliet, NY

    Askew, JC
    Materials engineer, mechanical engineer, chemical engineer, physical science technician, and metallurgist, Army Armament RD&E Center, Benet Laboratories, Watervliet, NY

    Kapusta, AA
    Materials engineer, mechanical engineer, chemical engineer, physical science technician, and metallurgist, Army Armament RD&E Center, Benet Laboratories, Watervliet, NY

    Young, GA
    Materials engineer, mechanical engineer, chemical engineer, physical science technician, and metallurgist, Army Armament RD&E Center, Benet Laboratories, Watervliet, NY


    Paper ID: STP24282S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP24282S


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