SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/eng-endurance-limit-steel-aluminum

Which metal typically has a fatigue endurance limit below which fatigue failure is not expected?

Many steels and other ferrous alloys; aluminum has no true endurance limit.

Start playing free

  1. Aluminum
  2. Steel ✔
  3. Both equally

Why: For many ferrous alloys, the S-N curve flattens to an endurance limit. Aluminum's curve keeps falling, so designers use a specified fatigue life rather than assuming unlimited cycles.

Huh, didn't know that: Fatigue tests can take days: at about 10 cycles per second, 10 million cycles takes about 11.6 days.

The dad joke
Steel has an endurance limit. My kids do not.
Like this card?
Play the game

References

Answer: Steel. For many ferrous alloys, the S-N curve flattens to an endurance limit. Aluminum's curve keeps falling, so designers use a specified fatigue life rather than assuming unlimited cycles.

  1. MIT OCW 3.11 Mechanics of Materials (Roylance): Fatigue ocw.mit.edu/courses/3-11-mechanics-of-materials-fall-1999/f678e01017186c53d45845ad93c07938_MIT3_11F99_fatigue.pdf
    In some materials, notably ferrous alloys
    Checked 2026-10-11.
  2. MIT OCW 3.11 Mechanics of Materials (Roylance): Fatigue ocw.mit.edu/courses/3-11-mechanics-of-materials-fall-1999/f678e01017186c53d45845ad93c07938_MIT3_11F99_fatigue.pdf
    For some other materials such as aluminum, no endurance limit exists
    Checked 2026-10-11.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

EngineeringSteel's Young's modulus is about 200 GPa. Aluminum's is about how much?EngineeringHow can metal fatigue break a part that never sees a load above its yield strength?EngineeringHow many base units does the International System of Units (SI) have?

That's stuff everyone should know.