Friction hydro pillar processing
Friction hydro-pillar processing (FHPP) is a solid-state joining technology which can be used for filling of surface and sub-surface cracks in thick metals. For example, FHPP was attempted for the first time to repair cracks in space shuttle external components of high-strength aluminum alloys.
Source: Wikipedia — Friction hydro pillar processing (CC BY-SA 4.0)