Definition
An increase in the strength and hardness of a metal caused by working it (bending, rolling, hammering, or drawing) at a temperature below its recrystallization point. The deformation distorts the metal's internal grain structure, making further deformation more difficult and the metal harder, stronger, and less ductile. Also called work hardening or cold working.
Plain English
When you bend or work a piece of metal cold, it gets harder and stronger in that area, but also more brittle. Bend it enough times and it will eventually crack.
Context Anchor
Seen in aircraft maintenance and repair discussions, especially when sheet metal, brackets, tubing, or other metal parts are bent, formed, straightened, or inspected for cracking.
Derivation
From 'strain' (deformation under load) and 'hardening' (becoming harder). The name describes exactly what happens: straining the metal hardens it.
Why Pilots Care
Mechanics must account for this when forming aircraft skins to avoid creating brittle areas that could crack in flight.
Analogy
Think of bending a paperclip back and forth. The bend point gets stiffer with each flex until it snaps. The metal didn't get weaker overall, it got harder and more brittle right where it was worked.
Intuition Check
Do not read strain here as emotional pressure. In this term, strain means a physical change in the shape of the metal. Hardening does not always mean the part is safer; a harder worked metal part can also become less flexible and more likely to crack.
Example Sentence 1
The mechanic rejected the bent aluminum bracket because attempting to straighten it would cause strain hardening and create a likely failure point.
Example Sentence 2
Strain hardening during the repair process increased the yield strength of the material but reduced its ductility.