How Laser Peening Works


Laser shock peening utilizes a pulsed laser to generate deep compressive residual stresses that improve metal fatigue life and damage tolerance.

What role does the laser play in the process?

A high-energy, short-duration laser pulse produces a rapidly expanding plasma burst on the part surface. The rapid rise of pressure generates a powerful compressive shockwave that propagates into the material.

What happens as the shockwave enters the work piece?

The shockwave consists of a strong primary front of compressive stress moving through the work piece. When the magnitude of this primary shockwave exceeds the material's dynamic yield strength (termed the Hugoniot Elastic Limit or HEL), it plastically deforms the microstructure and creates added dislocations in the material.

As the shockwave propagates through the target, it gradually loses energy to deformation and dislocation. The peak stress of the shockwave attenuates until the wave magnitude falls below the HEL, producing cold work over a gradient of depth in the material. The resultant plastic deformation and increase in dislocations produce compressive residual stresses that increase the material strength, and enhance resistance to cracking and failure.

How does plastic deformation generate residual stress?

The stresses produced by the shockwave permanently stretch the internal structure of the work piece in the target area. The surrounding material responds elastically to this deformation, leaving the processed region in a state of compressive residual stress. After a pattern of laser spots has been applied - usually with some percentage of spot overlap - the resultant gradient of plastic deformation defines the residual stress profile in the processed region.

Why are residual stresses beneficial?

When determining fatigue strength or damage tolerance of a component, the net stress state is a summation of all existing stress states including applied and residual stresses. As a general rule, most fatigue-prone components fail when they experience high tensile stress or repeated tensile loading concentrated on the part surface. Tensile stresses exacerbate microscopic flaws in the material, pulling tiny cracks apart until they grow into large fissures. When a component is enhanced with compressive residual stresses, it can withstand greater tensile forces before cracking and failure occurs. Stronger compressive residual stresses provide a greater buffer against tensile strain, and deeper compressive stresses inhibit crack initiation and propagation below the surface.

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