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Strength of Materials: Phases of Fatigue Failure

Phases of Fatigue Failure

The appearance of a fatigue failure is very similar to what a brittle fracture would look like. It however happens in phases, and because of this fatigue failure will normally happen unexpectedly. Also, it is important to note that different conditions such as stress concentrations can cause fatigue failure to occur faster than expected. A list of the phases can be seen below.

1. The first phase is introduction of micro-cracks due to the cyclic plastic deformation. These micro-cracks cannot be seen by the human eye, but continue to form as loading is applied then removed in a cyclical manner.

2. The next phase is when the micro-cracks form into macro-cracks. These cracks will form a parallel plateau like fracture on its surface. This is commonly known as beach marks or clam shell marks.

3. Finally, as the macro-cracks continue to grow the specimen will finally not be able to support the load and a sudden fracture of the material will occur.

Refer the figure below to see how the fatigue failure will progress through a specimen.

The process of a fatigue failure

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