Effect of surface rolling on fatigue behavior of a pearlitic ductile cast iron |
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Authors: | O Maluf M T Milan D Spinelli |
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Affiliation: | 1.Engineering School of S?o Carlos, Department of Materials, Aeronautics and Automotive Engineering,University of Sao Paolo,Sao Paolo,Brazil |
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Abstract: | Surface rolling is a mechanical treatment usually used in parts fabricated with steel and ductile cast iron, specifically
in stress concentration regions, to improve fatigue properties. This process hardens and introduces compressive residual stresses
to the surface of the material through the application of controlled strains, thus provoking a reduction of resulting tensile
stress at its surface under cyclic loading. This work deals with the effect of surface rolling on high cycle fatigue behavior
of a pearlitic ductile cast iron used in crankshafts by the automotive industry. Rotating bending fatigue tests were performed
in both smooth and notched specimens, the latter either with or without a surface rolling treatment. Compressive residual
stresses and heavy plastic deformation imposed on the surface grains due to cold work made difficult the nucleation and propagation
of the crack at the rolled surface of the notch. As a consequence, surface-rolled notch testpieces presented a higher endurance
limit (478 MPa) than both smooth (299 MPa) and notched (166 MPa) testpieces did. The surface rolling apparatus developed for
this work proved to be very efficient and simple, providing good control of parameters involved in the process (i.e., rolling
load, frequency, and number of revolutions). |
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Keywords: | ductile cast iron fatigue plastic deformation residual stress surface rolling |
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