Definition
The deformation, or change in shape or size, of a material caused by an applied stress. Strain is measured as the amount of change relative to the material's original dimension and has no units of its own.
Plain English
How much a material stretches, squashes, twists, or bends when a force is pushing or pulling on it.
Context Anchor
Seen in aircraft structures, materials, inspection, and repair discussions, especially when describing how parts react to loads.
Derivation
From Old French 'estreindre' and Latin 'stringere', meaning to draw tight or bind. The original sense of being pulled or stretched carries directly into the engineering meaning.
Why Pilots Care
Repeated or excessive strain on aircraft structures can lead to permanent deformation, cracks, or failure. Recognizing the difference between stress (the force) and strain (the resulting deformation) helps in understanding inspection findings and structural limits.
Analogy
A rubber band shows strain when it gets longer as you pull it. Aircraft parts are much stiffer, but the idea is the same: the force causes a measurable change in shape or size.
Grounding Statement
Picture a metal bracket being pulled just enough that it becomes slightly longer; that length change is strain.
Intuition Check
Strain does not mean stress or effort here. Stress is the force inside the material; strain is the shape change that force produces.
Example Sentence 1
When the wing flexes under load, the metal skin experiences strain proportional to the stress applied.
Example Sentence 2
Repeated high loads can cause permanent strain in fuselage skin panels.