How to Calculate the Fatigue Strength of Steel


Fatigue strength refers to the amount of strength of a material under cyclic loading. Fatigue is a phenomenon known to occur when any material or component is constantly being loaded and unloaded. After a certain point, cracks will start to form in the material being subjected to the loading and unloading, and over time the entire structure will start to fracture. The shape of a given structure is vital in determining the fatigue strength. A rounded structure with circular holes increases the fatigue strength. Sharp corners, on the other hand, reduce fatigue strength. Steel is one material that can be affected by fatigue, and the fatigue strength of steel can be calculated with a specific method.

Things You'll Need

  • Round piece of steel
  • Apply a constant bending stress to the round sample of the piece of steel. Make sure the sample is optimized for fatigue life.

  • Rotate the round piece of steel around the bending stress axis. Continue doing this until the piece fails.

  • Repeat the same process, running at least two more tests at varying stress levels of interest.

  • Record the data in a notebook and note all the results of each test as it is done.

  • Arrange all your noted statistics in an orderly manner and figure the expected number of cycles to failure at that stress level.

Tips & Warnings

  • Note in advance that steel alloys subjected to a cyclic stress level below the EL (properly adjusted for the specifics of the application) will not fail in fatigue. EL refers to the "endurance limit" and to the cyclic stress level any material can maintain for at the very least ten million cycles.

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