Identify the technique that does NOT serve as a valid method for raising the fatigue limit_______________?
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Answer: C. surface decarburisation
Explanation
Surface decarburisation depletes carbon from the outer metal layer, reducing hardness and strength. Lower surface carbon creates weak microstructural zones that readily initiate fatigue cracks. Since it degrades fatigue resistance, decarburisation is definitely not a method for raising fatigue limits. Fatigue limit is the maximum stress level a material can endure for infinite load cycles. Surface treatments aim to introduce compressive residual stresses or harden exterior metal layers. Decarburisation occurs unintentionally during high temperature forging or heat treatment in reactive atmospheres.
Automotive crankshafts and springs undergo rigorous surface inspection to detect harmful decarburisation layers. Machining or grinding away decarburised outer layers is standard practice to restore fatigue strength. Preventing surface carbon loss ensures structural components survive high cycle fatigue service. Cold working increases dislocation density and raises the fatigue limit of engineering alloys. Shot peening introduces beneficial compressive residual stresses that successfully enhance fatigue strength. Under-stressing progressively improves fatigue resistance through strain hardening training mechanisms.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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