SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/eng-neutral-axis-zero-stress

In a homogeneous beam under simple bending, where is normal bending stress zero?

At the neutral axis, which passes through the cross-section's centroid in this case.

Start playing free

  1. At the top surface
  2. At the neutral axis through the centroid ✔
  3. At the supports only

Why: For a homogeneous beam in simple bending, normal stress varies linearly from zero at the neutral axis to its greatest magnitude at the outer surfaces. The neutral axis passes through the cross-section's centroid.

Huh, didn't know that: The stress changes sign across the neutral axis, from tension to compression.

The dad joke
The neutral axis never takes sides in an argument between tension and compression.
Like this card?
Play the game

References

Answer: At the neutral axis through the centroid. For a homogeneous beam in simple bending, normal stress varies linearly from zero at the neutral axis to its greatest magnitude at the outer surfaces. The neutral axis passes through the cross-section's centroid.

  1. MIT OCW 3.11 Mechanics of Materials (Roylance): Stresses in Beams ocw.mit.edu/courses/3-11-mechanics-of-materials-fall-1999/96d839b02e4a6c63cf8031800e89cccd_MIT3_11F99_bstress.pdf
    At the transition between the compressive and tensile regions, the stress becomes zero; this is the neutral axis of the beam.
    Checked 2026-10-10.
  2. MIT OCW 3.11 Mechanics of Materials (Roylance): Stresses in Beams ocw.mit.edu/courses/3-11-mechanics-of-materials-fall-1999/96d839b02e4a6c63cf8031800e89cccd_MIT3_11F99_bstress.pdf
    the neutral axis is coincident with the centroid of the beam cross-sectional area
    Checked 2026-10-10.

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

Test yourself in the game

EngineeringA beam rests on two supports with a load in the middle. Which side is in tension?EngineeringWhy is an I-beam shaped like an I?EngineeringA 1/8 inch thick, 1 inch tall ruler is bent on edge instead of flat. How much stiffer is it?

That's stuff everyone should know.