Laser Shock Peening for Fatigue Resistance

Originally published in Surface Performance of Titanium, J. K. Gregory, H. J. Rack, and D. Eylon (eds.), (1996), pp. 217-230.

Authored by Allan H. Clauer

ABSTRACT
Laser shock peening produces a compressive residual stress in the surface of metallic materials, which significantly increases fatigue life in applications where failure is caused by surface-initiated cracks. Laser shock peening is applied by using a high energy pulsed laser to create a high amplitude stress wave or shock wave on the surface to be treated. This stress wave propagates into the material, causing the surface layer to yield and plastically deform, and thereby, develop a residual compressive stress. Where comparisons have been made to shot peening, the magnitude of the residual stresses at the surface are similar, but the compressive stresses from laser peening extend much deeper below the surface than those from shot peening. The resulting fatigue life enhancement is often greater for laser peering than it is for shot peening. In addition to fatigue strength improvement, laser peering can also locally strain harden thin sections of parts or strain harden a surface.

INTRODUCTION
Laser peening (LSP) or laser peening generally increases the resistance of metals and alloys to fatigue and fretting fatigue. It does this by using a high energy pulsed laser to produce residual compressive stresses and strain hardening into the surface of a laser peened part. The residual compressive stresses from laser shock peening extend deeper below the surface than those from shot peening, usually resulting in a significantly greater benefit in fatigue resistance after laser peening. Laser peening can also be used to locally strain harden thin sections of parts, and, if the part is thin enough, it can be strain hardened through the section thickness.

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