STP467: Fatigue Life Improvement Through Stress Coining Methods

    Speakman, ER
    Senior engineer and scientist, Douglas Aircraft Co., Long Beach, Calif.

    Pages: 17    Published: Jan 1970


    Abstract

    The use of a quick and economical new process, stress coining, results in an aircraft structure with a more balanced fatigue strength than was previously possible. Basically, the stress coining procedure, a proprietary method of the Douglas Aircraft Co., involves controlling the yielding of material inside holes and in the material surrounding holes and slots. Stress coining induces residual compressive stresses that offset load-induced tensile stresses concentrated around these load-carrying areas. The procedure can be used in highly stressed areas to increase fatigue life and resistance to stress corrosion of structural members. Salvage rework by reaming, stress coining, and installing an oversize fastener increases the remaining fatigue life to approach that of a virgin stress-coined structure. Fatigue life of test specimens for various aircraft has been improved by a factor of approximately four.

    Keywords:

    fatigue strength at N cycles, fatigue life, stress relieving, residual stress, stress corrosion, hole size, joints (junctions), tensile stress, fasteners, aircraft equipment, evaluation, tests


    Paper ID: STP26847S

    Committee/Subcommittee: E08.01

    DOI: 10.1520/STP26847S


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