Fatigue strength of Machined and Shot Peened Grey Cast Iron

• A common opinion is that cast iron, especially grey cast iron, is not as notch sensitive as steel therefore is not typically treated by shot peening to suppress crack initiation. For a heterogeneous material that also is brittle, just like grey cast iron, the shot peening parameters needed to induce beneficial surface residual stresses can be problematic to identify. Fatigue testing under uniaxial loading with an R value of -1, on mechanically polished and shot peened specimens, has been performed to determine the fatigue strength at 10(7) cycles as well as complete Wohler-curves. Two different types of specimen geometries were tested, one smooth and one notched specimen having k(t) equal to 1.05 and 1.33 respectively. With large shots and high peening intensity (heavy SP) the fatigue strength clearly decreased whereas small shots and low peening intensity (gentle SP) might have lowered the fatigue strength. A short annealing at 285 degrees after gentle SP increased the fatigue strength. The results are discussed and explained based on x-ray diffraction (XRD) measurements, i.e. residual stress and full width at half maximum profiles, as well as microstructural investigations using scanning electron microscope (SEM).

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering (hsv//eng)

Nyckelord

fatigue strength

grey cast iron

residual stresses

shot peening

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