Fatigue in Materials: Causes, Failure, and Analysis

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What is Fatigue?
Fatigue is the feeling of tiredness and reduce energy levels
while working. Fatigue is caused due to prolonged activity of
the same nature, basically by doing the same thing, in a cycle
or continuously for longer period of time. Fatigue reduces
performance of an individual, making one unable to do the
work which that person can do normally without any problem.
But does Materials also experience Fatigue?
• Yes, they do. It is seen that when materials are stressed
by fluctuating loads(cyclic stress) for long period of time
they tend to fail at a much lower value of its Ultimate
strength [1].
• It is statistically seen that fatigue accounts for nearly 90%
of all engineering failures.

What causes fatigue in Materials?
• Fatigue is observed in ductile materials with clear crack
propagation. Since brittle materials will not give much
deformation and will fail catastrophically after the crack
initiation has taken place.
• In any materials there will be microscopic flaws (E.g.
Voids, slip planes, surface defects, material inclusions
etc.).
• These flaws become region of stress concentration
when the it is subjected to some external forces.
• At this point the stress will become so high that it will
start to form microscopic voids in the material.
• Fatigue typically starts from the surface of any material,
from surface flaws, sharp corners, notches, cracks etc.