Definition
Forces acting in opposite directions along parallel lines, tending to slide one part of a material past an adjacent part. A shear load attempts to cut a fastener or structural member rather than stretch or compress it.
Plain English
Two forces pushing in opposite directions, side by side, that try to slice something apart — like the action of a pair of scissors.
Context Anchor
Seen in aircraft maintenance, especially when cutting aluminum sheet for panels, patches, or small repair parts.
Derivation
From Old English 'sceran,' meaning to cut or divide. The word still carries that cutting action — shear forces don't pull or squeeze, they slice.
Why Pilots Care
Bolts, rivets, and pins in an aircraft are often loaded in shear. Using a hardware item rated for tension where shear strength is required can lead to structural failure.
Analogy
Think of a pair of scissors closing on a piece of paper. The two blades move in opposite directions along parallel paths, and the paper is cut between them. That sliding, opposing action is shear.
Intuition Check
Do not confuse shears with wind shear or shear force. Here, shears are cutting tools used on material.
Example Sentence 1
The clevis bolt is loaded in shear, so it must be installed with the threaded portion clear of the bearing surface.
Example Sentence 2
When fabricating a new access panel, shears let the mechanic make smooth curves without distorting the metal.