Materials scienceLesson 4 of 4 in the course Machine design

Material Fatigue: Crack Growth, Life Prediction, and Prevention

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces material fatigue and explains the sequence from initial damage to final fracture. Understanding these stages helps explain why components can fail after repeated use, even when each individual load is below the material’s yield strength.

Fatigue is the initiation and propagation of cracks caused by repeated or fluctuating loading. A component may fail under repeated stresses much lower than the stress needed to cause immediate yielding in a single application. Fatigue damage is irreversible: resting a component does not restore the material.

All flashcards

What is fatigue in materials?
Fatigue is the progressive initiation and growth of cracks caused by repeated or fluctuating loads. It can lead to failure even when individual stresses are below the material’s yield strength.
What are the main stages of fatigue failure?
Crack initiation, slow Stage I growth, faster Stage II growth, and ultimate failure when the remaining section cannot carry the load.
What happens during Stage I crack growth?
The crack grows relatively slowly along crystallographic planes, commonly in directions associated with high shear stress.
What are persistent slip bands?
They are localized regions of repeated slip in a metal. Their surface intrusions and extrusions can act as tiny stress concentrators where cracks initiate.
Why can fatigue failure seem sudden?
Initiation and early crack growth can remain microscopic and difficult to detect, so a large portion of the damage may accumulate unseen before final fracture.

Quiz questions

  1. In conventional Miner's rule, what value is commonly used for cumulative damage at failure?Answer: A damage sum of 1
  2. Which parameters are commonly used in high-cycle fatigue testing when behavior is mostly elastic?Answer: Stress-based parameters
  3. What can happen when the stress intensity factor at a crack tip exceeds the material's fracture toughness?Answer: The crack can grow rapidly and unstably
  4. What is a common effect of a sufficiently large overload on fatigue crack growth?Answer: A brief increase in growth followed by reduced growth
  5. What is central to damage-tolerant design?Answer: Predicting flaw growth and inspecting before cracks become critical

Based on the Wikipedia article Fatigue (material), licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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