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Research Papers

Improvement of the Fatigue Behavior of Stainless Steel Substrates by Low Pressure Fluidized Bed Peening (FBP)

[+] Author and Article Information
M. Barletta1

Dipartimento di Ingegneria Meccanica, Università degli Studi di Roma Tor Vergata, Via del Politecnico, 1-00133 Roma (I), Italybarletta@ing.uniroma2.it

1

Corresponding author.

J. Eng. Mater. Technol 133(2), 021018 (Mar 22, 2011) (9 pages) doi:10.1115/1.4003486 History: Received March 17, 2010; Revised November 30, 2010; Published March 22, 2011; Online March 22, 2011

This study investigates the effectiveness of fluidized bed peening (FBP) to improve the fatigue behavior of axial-symmetric stainless steel substrates. The substrates were rotated at moderate speed inside a fluidized bed of stainless steel media. Their fatigue failure was determined by rotating bending testing procedure. The number of cycles to fracture was plotted versus the maximum amplitude of alternating stress for fluidized bed peened and unpeened substrates. The effect of peening time was also looked into. FBP was found to definitely improve the number of cycles to fracture. Fatigue life was normally increased of four to five times, although improvements up to an order of magnitude were detected. Hardness measurements, profilometry, scanning electron microscopy, and X-ray diffractometry allowed interpreting the improvement of the fatigue behavior of the peened substrates. After FBP, the substrates surface was characterized by a higher hardness, a smoother and less defective morphology, as well as a beneficial compressive residual stress. Therefore, the improvement in surface and microstructural properties of the peened substrates induced a related increase in their fatigue life. Peening time was also found to influence the fatigue behavior of the substrates, although the sharpest variations in the number of cycles to fracture were observed at the beginning of the fluidized bed process. Based on the previous experimental findings, approximate analytical models, very useful for automation and process control, were proposed, thus providing to the practitioners first hints on how to best set FBP process parameters.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Fatigue test sample

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Figure 2

Fluidized bed experimental apparatus

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Figure 3

3D maps of the morphology of AISI 316 L substrate after 4 h FB treatment

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Figure 4

Roughness parameters before and after FB treatment

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Figure 5

Surface profiles before and after FB treatment

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Figure 6

Hardness depth profiles according to FB processing time

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Figure 7

Fe-γ(111) peak of AISI 316 L substrate before and after 4 h FB treatment

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Figure 8

FWHH broadening depth profiles according to FB processing time

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Figure 9

Residual stresses’ depth profiles according to FB processing time

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Figure 10

Fe-γ(111) and Fe-α(110) peaks (grazing incidence ω=1) of AISI 316 L substrate after 4 h FB treatment

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Figure 11

Number of cycles to rupture versus FB processing time with stress amplitude

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Figure 12

Stress amplitude versus number of cycles to rupture for untreated substrate and 4 h FB treated substrate

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Figure 13

Fracture cross section of the 4 h FB treated substrate

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Figure 14

Fracture cross section of the untreated substrate

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