STP1049

    Environmental and Microstructural Influence on Fatigue Propagation of Small Surface Cracks

    Published: Jan 1990


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    Abstract

    The propagation of small surface cracks has been studied on a high-strength aluminum alloy 7075 in peak aged (T651) and overaged (T7351) conditions. Tests were performed at a load ratio R = 0.1 and a frequency of 35 Hz in ambient air and in vacuum. Small crack growth was monitored by mean of replicas. The behavior of small cracks is compared to that of long and short through cracks and discussed on the basis of closure measurements performed on long cracks. A strong influence of environment on small crack growth has been shown which is similar to that observed for through cracks in the low rate range (<10-8 m/cycle). The lower resistance observed in air has been related to water vapor embrittlement as previously shown for long cracks. The influence of microstructure at the scale of grain size has been shown to be large on crystallographic Stage I propagation observed in vacuum on the 7075 T651, but weak on Stage II propagation observed on the 7075 T651 in air and on the 7075 T7351 in both environmental conditions.

    Keywords:

    fatigue (materials), cracking, environmental effects, aluminum alloys, fatigue crack propagation, surface cracks, microstructure


    Author Information:

    Petit, J
    Directeur de Recherche and maitre de Conference, Laboratoire de Mecanique et de Physique des Materiaux, UA 863 au CNRS, E. N. S. M. A., Poitiers,

    Zeghloul, A
    Directeur de Recherche and maitre de Conference, Laboratoire de Mecanique et de Physique des Materiaux, UA 863 au CNRS, E. N. S. M. A., Poitiers,


    Paper ID: STP24074S

    Committee/Subcommittee: G01.06

    DOI: 10.1520/STP24074S


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