STP1004

    X-ray Diffraction and Acoustic Emission Study of Fatigue Damage in Aluminum Alloys

    Published: Jan 1988


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    Abstract

    The damage that leads to crack initiation under fatigue loading generally occurs at or near the surface. The macrostresses and microstrains induced by machining and surface treatments such as shot peening play an important role in the initiation process. The initial distribution and subsequent evolution of these stresses and strains also influence the growth of fatigue damage. A detailed study, carried out using two aluminum alloys (2024 T351 and 7075 T7351) with electrolytically polished, milled, or shot peened surfaces, has been undertaken at microscopic and macroscopic levels by X-ray measurements of residual stresses at each step of damage development. Acoustic emission has been used to detect the three stages of damage growth: plastic deformation of the surface, microcrack formation, and macrocracking.

    The experiment pointed to the conclusion that the damage leading to crack initiation occurs in the following manner: (1) cyclic cold working of the surface with a rapid evolution of residual stresses, (2) stabilization of these stresses and plastic deformation of the surface layers, (3) the appearance of the first microcracks without any change in the residual stresses, and then, (4) the ascendency of one or two macrocracks with complete relaxation of the macrostresses in the close neighborhood of this macrocrack.

    Keywords:

    residual stresses, x-ray diffraction, fatigue, aluminum alloys, shot peening, acoustic emission


    Author Information:

    Bathias, C
    Professor, Université de Technologie de Compiègne (U. T. C.), U.A. CNRS 910 Centre De Recherche de Royallieu, Compiegne,

    Bonnafe, JP
    Professor, Université de Technologie de Compiègne (U. T. C.), U.A. CNRS 910 Centre De Recherche de Royallieu, Compiegne,

    Lebrun, JL
    Associate professor and graduate student, Ecole Nationale Supérieure d'Arts et Métiers (E. N. S. A. M.), U.A. CNRS, Paris,

    Maeder, G
    Associate professor and graduate student, Ecole Nationale Supérieure d'Arts et Métiers (E. N. S. A. M.), U.A. CNRS, Paris,


    Paper ID: STP17170S

    Committee/Subcommittee: E08.04

    DOI: 10.1520/STP17170S


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