Definition
A crack in a structural component caused by repeated or sustained loads that exceed the material's ability to flex without damage. Stress cracks typically begin at a point of high stress concentration -- such as a fastener hole, a sharp corner, or an existing surface flaw -- and grow progressively each time the load is applied.
Plain English
A small split or fracture in metal or other material that forms because the part has been bent, pulled, or vibrated more than it can take. Once it starts, it tends to get longer over time as the part keeps being used.
Context Anchor
Seen during preflight inspections, maintenance inspections, and logbook write-ups, especially around metal skins, engine parts, propellers, windshields, fairings, and areas near fasteners.
Derivation
Stress comes from the Latin strictus, meaning 'drawn tight' -- the same root as 'strict.' In engineering, stress is the internal force inside a material when something pulls, pushes, or twists it. A stress crack is literally a crack caused by that internal force exceeding what the material can handle.
Why Pilots Care
Undetected stress cracks can grow until a structural part fails, creating a serious safety risk in flight.
Analogy
Like a paperclip that eventually snaps after being bent back and forth many times.
Grounding Statement
Picture a thin piece of metal being bent back and forth many times until a tiny split starts at one edge; that split is the kind of failure described by stress crack.
Intuition Check
A stress crack is not just any scratch or surface mark. It is a real split in the material caused by force, vibration, bending, heat change, or repeated use.
Example Sentence 1
During preflight, the pilot found a small stress crack near a rivet on the engine cowling and grounded the aircraft until a mechanic could inspect it.
Example Sentence 2
Continued vibration from an unbalanced propeller can create stress cracks in the hub over time.