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    Volume 5, Issue 3 (December 2016)

    Special Issue Paper

    High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets

    (Received 6 November 2015; accepted 8 February 2016)

    Published Online: 06 December 2016

    CODEN: MPCACD

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    Abstract

    Some parts of electrical machines are built from stacks of thin steel sheets, for which the coarse grain microstructure allows for minimizing magnetic losses. The fabrication process of these parts usually involves punching operations that generate important defects on the edges. Since these alterations may result in a degradation of the fatigue strength, this study aims at elaborating on a fatigue design strategy for such punched parts. To reach this objective, high cycle fatigue tests are performed on different specimens with either punched or polished edges. The results show a significant decrease of the fatigue strength for punched specimens. Scanning electron microscope observations of specimen facture surfaces reveal that defects on punched edges are at the origin of the fatigue cracks. The influence of temperature is also investigated. Fatigue tests are performed at ambient temperature (20°C) and at 180°C. According to the experimental results, no significant influence on the median fatigue strength is observed. Since crack initiation always occur on the edges, additional investigations are performed to characterize how edges are altered by punching operations. Residual stresses are determined on punched edges using x-ray diffraction techniques. As a consequence of punching, important tensile residual stresses exist along the loading direction. In association with the stress concentration caused by geometrical defects, residual stresses promote crack initiation and fast crack propagation. For a better understanding of crack initiation, edge geometries are scanned with a 3D optical profilometer, allowing us to identify the critical defect. It is found that the typical defect size is comparable to the grain size.


    Author Information:

    Dehmani, Helmi
    Emerson-Leroy Somer, Angoulême,

    Arts et Métiers ParisTech, I2M, CNRS, Esplanade des Arts et Métiers, Talence,

    Arts et Métiers ParisTech, LAMPA, Angers,

    Brugger, Charles
    Arts et Métiers ParisTech, I2M, CNRS, Esplanade des Arts et Métiers, Talence,

    Palin-Luc, Thierry
    Arts et Métiers ParisTech, I2M, CNRS, Esplanade des Arts et Métiers, Talence,

    Mareau, Charles
    Arts et Métiers ParisTech, LAMPA, Angers,

    Koechlin, Samuel
    Emerson-Leroy Somer, Angoulême,


    Stock #: MPC20150063

    ISSN:2165-3992

    DOI: 10.1520/MPC20150063

    Author
    Title High Cycle Fatigue Strength of Punched Thin Fe-Si Steel Sheets
    Symposium ,
    Committee E08