Importance of Residual Stresses and Surface Roughness regarding Fatigue of Titanium Forgings

    Volume 7, Issue 2 (February 2010)

    ISSN: 1546-962X

    CODEN: JAIOAD

    Published Online: 3 December 2009

    Page Count: 11


    Oberwinkler, B.
    Institute of Mechanical Engineering, Univ. of Leoben, Leoben,

    Riedler, M.
    Böhler Schmiedetechnik GmbH & Co. KG, Kapfenberg,

    Eichlseder, W.
    Institute of Mechanical Engineering, Univ. of Leoben, Leoben,

    (Received 19 May 2009; accepted 20 October 2009)

    Abstract

    This paper presents the results of a long-term research program aimed at developing qualitative and quantitative design guidelines for the use of mechanical surface treatments designed to improve the fatigue life of structural components. High cycle fatigue tests were performed on planar four-point bending specimens derived from Ti-6Al-4V pancake forgings with a mill-annealed microstructure. The high cycle fatigue behavior of specimens with different surface conditions (as-forged and machined) in both an unpeened and a shot peened state was compared. In order to assess the fatigue failure mechanisms, detailed investigations of the surface layers were carried out. The as-forged surface state exhibits a stress distribution with significant compressive stresses near the surface, resulting in equilibrium tensile stresses in the depth. When the tensile stresses were exposed by machining a bordering surface, a distinct decrease in the fatigue strength was observed. In such cases, a shot peening treatment was shown to improve the fatigue strength. Square edges lead to a decrease in the fatigue strength, which could be aggravated by shot peening.


    Paper ID: JAI102534

    DOI: 10.1520/JAI102534

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    Author
    Title Importance of Residual Stresses and Surface Roughness regarding Fatigue of Titanium Forgings
    Symposium Ninth International ASTM/ESIS Symposium on Fatigue and Fracture Mechanics (37th ASTM National Symposium on Fatigue and Fracture Mechanics), 2009-05-22
    Committee E08