Definition 1 of 2
Definition
A foreign particle or non-metallic substance trapped inside a metal during its manufacture. Common inclusions include slag, oxides, sulfides, and other impurities that become embedded in the metal as it solidifies. Inclusions create weak spots that can act as starting points for cracks, corrosion, or fatigue failure.
Plain English
A bit of unwanted material stuck inside a piece of metal. It got there when the metal was made and was never removed. These trapped specks make the metal weaker at that spot.
Context Anchor
Seen in aircraft maintenance, inspection, welding, casting, bonding, and repair discussions when judging whether a part is sound or defective.
Derivation
From the Latin includere, meaning 'to shut in' or 'enclose.' The word describes something that has been closed inside the metal — trapped during forming and never released.
Why Pilots Care
Inclusions act as stress risers and can initiate fatigue cracks in critical components such as engine cases, landing-gear forgings, or propeller blades.
Grounding Statement
Picture a small air bubble or speck trapped inside hardened glue; the trapped spot is the inclusion.
Intuition Check
Do not read inclusion as simply “something included” in a normal or useful way. In this maintenance sense, it usually means something unwanted trapped inside a material.
Example Sentence 1
The cracked turbine blade was traced to an inclusion that had been present in the metal since the part was forged.
Example Sentence 2
Laboratory analysis traced the propeller failure to a subsurface inclusion that had grown into a fatigue crack.