Surface enhancement is the introduction of a surface layer of compressive residual stress to minimize sensitivity to fatigue or stress corrosion failure mechanisms, resulting in improved performance and increased life of components. Surface enhancement methods include:
- Shot Peening
- Controlled Coverage Shot Peening
- Laser Shock Peening (LSP)
- Deep Rolling
- Low Plasticity Burnishing (LPB)
- Controlled Plasticity Burnishing
With the exception of simple overload, failures initiate from the surface of a part by some combination of fatigue, stress corrosion cracking, or corrosion fatigue. Failures are often exacerbated by a crack initiating damage mechanism such as fretting, corrosion pitting, intergranular corrosion, or foreign object damage (FOD). The surface of a component is inherently weaker than the interior because the free surface lacks the constraint imposed by fully surrounding material. Therefore, as is generally observed, fatigue cracks will initiate at the surface. Internal fatigue crack initiation requires high internal residual tensile stress and/or a discontinuity such as an inclusion, void, or other internal flaw to act as a "surface" for initiation.Stress corrosion cracking (SCC) under static load, and its dynamic cousin corrosion fatigue, which combines cyclic crack growth with stress corrosion cracking, also necessarily originate at the surface. Only at the surface do the combination of susceptible material, a corrosive environment, and tension exceeding the threshold stress level for SCC occur.