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Research Papers

Stability of Residual Stresses Created by Shot Peening in Monotonic Loading and at the Presence of Load Reversals—Experiments and Modeling

[+] Author and Article Information
K. Dalaei1

Materials and Manufacturing Technology Department,  Chalmers University of Technology, SE-412 96 Gothenburg, Swedendalaei@inbox.com

C. Persson, B. Karlsson

Materials and Manufacturing Technology Department,  Chalmers University of Technology, SE-412 96 Gothenburg, Sweden

1

Corresponding author.

J. Eng. Mater. Technol 134(2), 021010 (Mar 27, 2012) (9 pages) doi:10.1115/1.4006133 History: Received August 08, 2011; Revised February 02, 2012; Published March 26, 2012; Online March 27, 2012

As a method for mechanical surface treatment, shot peening has been widely used to improve the fatigue strength of materials. However, the influence of residual stresses introduced by shot peening depends on their stability. The stability of residual stresses during fatigue may be studied in two stages: the first cycle and successive cyclic loading. In this study the stability and development of the residual stresses during the first cycle of strain controlled fatigue of normalized steel was investigated. The influence of total strain amplitude and the loading direction was studied. The residual stresses were obtained using the x-ray diffraction technique. It was shown that the stability and relaxation of the residual stresses depend both on the amount and the direction of the loading stresses. Finite element modeling (FEM) was used to rationalize the experimental data. Very good agreement between the experimental and FEM results were observed.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

The geometry of the fatigue specimen (in mm)

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Figure 2

(a) In-depth distributions of the longitudinal residual stresses and the FWHM of the x-ray peak recorded for peened specimens before tests [10]. (b) The distribution of the micro hardness and the corresponding calculated yield strength.

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Figure 3

(a) Compound stress-strain curves after straining in tension and compression to 0.25%, 0.4%, 0.6%, and 1% total strain. The amount of remaining plastic strain for tests at 0.25% is 0.008%. (b) The stress-strain curves after straining to 1% and 2% total strain in tension and in compression. ɛp stands for plastic strain.

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Figure 4

(a) and (b) Schemes showing straining conditions starting in tension and compression, respectively. (c) and (d) Corresponding stress-strain curves obtained for 1% total strain amplitude experiments.

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Figure 5

The axi-symmetric model after application of the compressive load in the radial direction. The Z (transverse) direction is perpendicular to the paper.

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Figure 6

Experimental and calibrated stress-strain curves for unpeened specimens tested at 0.4%, 0.6%, and 1% strain amplitudes.

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Figure 7

Experimental and modeling distribution of the residual stresses in the shot peened cylindrical specimen.

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Figure 8

(a) The relaxation of the surface residual stresses in the longitudinal and transverse directions after monotonic loading in tension and compression, and (b) the corresponding FWHM of the x-ray peak

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Figure 9

The experimental (solid symbols) as well as the modeling (open symbols) residual stresses after different quartiles of straining in (a) the longitudinal direction start in tension, (b) the longitudinal direction start in compression, (c) the transverse direction start in tension, and (d) the transverse direction start in compression

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Figure 10

(a) Schematic representation of the plastic deformation in an element taken from the very top surface of a shot peened specimen. The dotted line represents the element before plastic deformation; the dashed line shows the influence of plastic deformation. However, being constrained by the bulk of material, the surface element cannot freely deform, contracting to the final dimension shown by the solid line. (b) Corresponding stress-strain curve. The Z direction is perpendicular to the paper (corresponding to the transverse direction).

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Figure 11

The surface, core, and compound stress-strain curves in monotonic (a) tensile, and (b) compressive loading, obtained by FEM

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Figure 12

FEM simulation of one full strain cycle started in (a) tension, and (b) compression. Stress-strain curves for the compound (solid line), core (dotted line), and surface (dashed line). The same points marked in Figs. 4 and 4 are marked as 1 to 4 here.

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