Effects of Shot Peening on Fretting Fatigue Crack Initiation Behavior

Abstract

This study analyzes the effects of shot peening on the crack initiation behavior under fretting loading by using a numerical method. The residual stress relaxation and the contact stress evolution are both considered. The crack initiation life is predicted by the critical plane Smith⁻Watson⁻Topper (SWT) model. Considering that the fretting contact region has a high stress gradient along the depth direction, the process volume approach is adopted to calculate the SWT parameters. The results show that the remaining residual stress after relaxation strongly affects crack initiation life. The remaining residual stress decreases with the increase of fatigue loading, and the effect of shot peening on the improvement of crack initiation life is more obvious under smaller fatigue loading. Furthermore, under smaller fatigue loading, the crack initiation life of specimens with high shot peening intensity is longer than that of specimens with low shot peening intensity. However, the opposite phenomenon appears when the fatigue loading is large enough.

Keywords: crack initiation; fretting loading; residual stress relaxation; shot peening.

Figure 1

Residual stress versus depth for different shot-peened specimens.

Figure 2

Schematic illustration of a typical indentation load-depth (P-h) curve.

Figure 3

The flow chart of Dao’s analysis algorithms [18].

Figure 4

Yield strength versus depth for different shot-peened specimens.

Figure 5

Pin-on-plate rotating wear experiment device.

Figure 6

The section of wear scar measured by 3D surface profiler.

Figure 7

Two-dimensional fretting fatigue finite element model.

Figure 8

Schematic of radial shape process volume approach.

Figure 9

Distribution of (a) wear profile and (b) contact pressure on the contact surface in 2000 loading cycles under fatigue loading ${\sigma }_{\mathrm{B}}=450$ MPa.

Figure 10

Distribution of average residual stress (by using the process volume method) in 2000 loading cycles under fatigue loading ${\sigma }_{\mathrm{B}}=450$ MPa.

Figure 11

The accumulated damage on the contact surface after material failure under fatigue loading ${\sigma }_{\mathrm{B}}=450$ MPa.

Figure 12

The evolution of accumulated damage at the crack initiation location with increasing cycle number under fatigue loading ${\sigma }_{\mathrm{B}}=450$ MPa.

Figure 13

The accumulated damage on the contact surface after material failure under fatigue loading ${\sigma }_{\mathrm{B}}=400$ MPa.

Figure 14

The evolution of accumulated damage at the crack initiation location with increasing cycle number under fatigue loading ${\sigma }_{\mathrm{B}}=400$ MPa.

Figure 15

The accumulated damage on the contact surface after material failure under fatigue loading ${\sigma }_{\mathrm{B}}=350$ MPa.

Figure 16

The evolution of accumulated damage at the crack initiation location with increasing cycle number under fatigue loading ${\sigma }_{\mathrm{B}}=350$ MPa.

Figure 17

Distribution of average residual stress (by using the process volume method) on the contact surface for (a) 0.1 mmA and (b) 0.2 mmA shot-peened specimens under fatigue loading ${\sigma }_{\mathrm{B}}=350$ MPa.

Figure 18

Residual stress versus the material layer depth with 20,000 and 80,000 cycles for different shot-peened cases.