STP436

    Special Fractographic Techniques for Failure Analysis

    Published: Jan 1968


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    Abstract

    In order to assist the investigator of service failures, work was performed using electron fractographic methods to resolve three separate problems that have not been solvable using the more conventional macro- or light microscopic techniques. Three independent problems were examined, and solutions were achieved. These were: (1) determination of fracture direction in thin sheet metal components, (2) differentiating between hydrogen embrittlement and stress corrosion in high-strength steels, and (3) determination of applied cyclic stress as a function of fatigue striation spacing.

    The results of the investigation indicated that: 1. Fracture direction in thin sheet-metal components can be determined by replicating the acute angle shear lip. The direction of open dimples with respect to the fracture edge indicated the fracture direction in the plane of fracture. 2. There is reasonable evidence that stress corrosion and hydrogen embrittlement fractures in high-strength steel can be separated by the following: (a) Hydrogen embrittlement fractures initiated subsurface, while stress corrosion fractures initiated at the free surface. (b) The corrosion attack in hydrogen embrittlement fractures, if present, was random while in stress corrosion the oxidation products were more concentrated at the nucleus. (c) Stress corrosion fractures had stronger indications of secondary cracking than hydrogen embrittlement failures. (d) The fracture features on the hydrogen embrittled specimens were more clearly defined than those on the stress corrosion fractures. 3. A correlation was established between cyclic stress and fatigue striation spacing for several aluminum alloys over a wide range of alternating and mean stresses in thicknesses of 0.050 and 0.500 in. The correlation was empirically derived.

    Keywords:

    electron microscope, fractography, failure analysis, fracture, replication methods, hydrogen embrittlement, stress corrosion, fatigue (materials), crack propagation rates, fracture toughness, aluminum, steel, sustained load testing, intergranular fracture, cadmium plating, high-strength materials


    Author Information:

    Whiteson, BV
    Chief, Metallurgy Development Section; group leader, Electron Microscope Laboratory; research and development engineer, Electron Microscope Laboratory; and group leader, Development Metallurgypersonal member of ASTM, Douglas Aircraft Co., Santa Monica, Calif.

    Phillips, A
    Chief, Metallurgy Development Section; group leader, Electron Microscope Laboratory; research and development engineer, Electron Microscope Laboratory; and group leader, Development Metallurgypersonal member of ASTM, Douglas Aircraft Co., Santa Monica, Calif.

    Kerlins, V
    Chief, Metallurgy Development Section; group leader, Electron Microscope Laboratory; research and development engineer, Electron Microscope Laboratory; and group leader, Development Metallurgypersonal member of ASTM, Douglas Aircraft Co., Santa Monica, Calif.

    Rawe, RA
    Chief, Metallurgy Development Section; group leader, Electron Microscope Laboratory; research and development engineer, Electron Microscope Laboratory; and group leader, Development Metallurgypersonal member of ASTM, Douglas Aircraft Co., Santa Monica, Calif.


    Paper ID: STP32005S

    Committee/Subcommittee: E08.03

    DOI: 10.1520/STP32005S


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