FOD is a term frequently used in the aircraft industry to describe damage occurring on components as a result of non-regular operating conditions. For instance, aircraft operating on a runway have the potential to ingest rocks and debris into the engine intake systems. Upon ingestion, the debris may damage the engine blades leading to dents, nicks, and partial fractures. These FOD induced defects can lead to poor performance, but more concerning, is unanticipated failure via fatigue cracking from stress concentrations. Processing via laser peening induces such deep residual stresses that FOD concerns can be reduced to negligible concern.
Certain alloys commonly in use, especially 5xxx series aluminum, can develop sensitization, making them more vulnerable to stress corrosion and cracking. High temperatures can promote an electrochemical reaction in which alloy particles – e.g. magnesium or iron – migrate to the boundaries between grains of aluminum or stainless steel. This promotes separation of individual grains of metal, causing intergranular corrosion and cracking. Exposure to saltwater can further promote corrosion of sensitized metals. Laser peening does not treat sensitization itself, but it can impart compressive residual stresses in order to mitigate the resulting corrosion and cracking, even after some metals have experienced sensitization.