Residual Stress Field of a Single Edge Notch Specimen after Laser Shock Peening and Shot Peening Treatment

Abstract

Laser shock peening (LSP) is a reliable, repeatable, and successful surface technique for introducing high magnitude, deep compressive residual stresses that can significantly increase the fatigue life of metallic components. However, depending upon how the LSP treatment is applied, the induced residual stresses can result in the undesirable deformation of the part. In this work, traditional shot peening has been applied over LSP as a means to optimize the stress distribution at the surface of a part while constraining deformation. A single edge notch test specimen of AA7075 was laser peened local to the notch region and then shot peened over the entire central region. The resulting residual stress distribution has been characterized using neutron diffraction to measure the stress distribution in the bulk, and it was compared with (1) incremental center hole drilling to measure the stress distribution up to depths of ∼1 mm and (2) near-surface stresses obtained in a previous X-ray diffraction (XRD) study on nominally identical specimens subjected to the same surface treatments. For regions where the two techniques overlap, the residual stresses are in good agreement (within uncertainty). Comparing the bulk stresses obtained from neutron diffraction in this study and XRD data published elsewhere, it can be shown that shot peening applied after LSP has a profound effect on near-surface stresses; however, these effects disappear at depths of ∼0.7 mm or more.

Strengthening effect of laser shock peening on 7075-T6 aviation aluminum alloy

“…The U values of five kinds of spot array were calculated based on Figure 23 and equation (4), and as shown in Table 4.…”

“…The target material plastically deforms when the pressure of shock waves is larger than its Hugoniot elastic limit. Compared with shot peening, LSP has the advantages of deeper strengthening layer, 4 better strengthening effect and smaller target surface roughness. 5 Laser shock peening is widely used in surface treatment of aluminum alloy.…”