If a material fractures below its yield point, the failure stems from___________________?
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Answer: B. fatigue
Explanation
Fatigue failure occurs when mechanical components experience repeated cyclic stress loading over time. Microscopic cracks initiate and propagate gradually until sudden structural fracture occurs. Crucially, maximum cyclic stress levels remain well below the static yield point of the material. Fatigue represents the most common cause of unexpected mechanical failure in operational machinery. S-N curves plot stress amplitude versus cycles to failure for specific engineering materials. Surface finish, residual stresses, and operational environment heavily influence material fatigue limits.
Rotating shafts, aircraft wings, and vehicular suspension links are prone to fatigue cracking over long service lives. Engineers apply safety factors and surface treatments like shot peening to enhance component fatigue resistance. Periodic nondestructive testing detects microscopic fatigue cracks before catastrophic structural failure happens. Straining past yield points causes permanent plastic deformation rather than sudden low-stress fatigue fracture. Creep involves slow plastic deformation under constant high temperature loads over extended periods. Sudden impact loading typically exceeds yield limits, whereas fatigue accumulates slowly through millions of cycles.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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