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Questions and Answers
What are the three stages involved in fatigue failure?
What are the three stages involved in fatigue failure?
- Crack formation, crack closure, final fracture
- Crack growth, plastic deformation, final failure
- Crack formation, crack growth, final fracture (correct)
- Crack initiation, elastic deformation, final rupture
What does the Endurance limit represent in fatigue design?
What does the Endurance limit represent in fatigue design?
- Threshold stress below which a component won't fail due to fatigue (correct)
- Stress range that causes immediate fracture
- Minimum stress required to initiate crack growth
- Maximum stress a component can withstand before failure
How does high cycle fatigue differ from low cycle fatigue?
How does high cycle fatigue differ from low cycle fatigue?
- Low cycle fatigue consists of cycles with both elastic and plastic deformation (correct)
- High cycle fatigue consists of cycles with no deformation
- High cycle fatigue involves fewer cycles with plastic deformation
- Low cycle fatigue involves more cycles and elastic deformation
What is the purpose of adjusting S-N curves published in engineering codes?
What is the purpose of adjusting S-N curves published in engineering codes?
Which method is used to simplify complex stress spectra into constant amplitude cycles?
Which method is used to simplify complex stress spectra into constant amplitude cycles?
How does mean stress affect fatigue life in testing?
How does mean stress affect fatigue life in testing?
What does Miner's rule calculate in relation to fatigue failure assessment?
What does Miner's rule calculate in relation to fatigue failure assessment?
What approach is used to determine fatigue life in structures with existing cracks?
What approach is used to determine fatigue life in structures with existing cracks?
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Study Notes
- Fatigue failure is a common cause of mechanical engineering failures worldwide, occurring in components subjected to time-varying loads.
- Fatigue failure is a three-stage process involving crack formation, crack growth, and final fracture.
- To predict fatigue failure, fatigue tests are conducted by subjecting components to stress cycles and plotting the results on an S-N curve.
- Endurance limit is an important parameter in fatigue design, representing the stress range below which a component will not fail due to fatigue.
- Differentiate between high cycle fatigue (more than 10,000 cycles) and low cycle fatigue (fewer cycles with elastic and plastic deformation).
- S-N curves published in engineering codes are adjusted downwards to reduce the probability of failure.
- Mean stress in fatigue testing can affect fatigue life, with tensile mean stress typically resulting in a shorter fatigue life.
- Goodman diagram is used to adjust the endurance limit for mean stress effects to determine if a component will have an infinite life.
- Rainflow counting method simplifies complex stress spectra into constant amplitude cycles, and Miner's rule calculates cumulative damage to assess fatigue failure.
- Linear Elastic Fracture Mechanics approach is used to determine fatigue life in structures with existing cracks by calculating critical crack size and growth time.
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