When a beam is under pure bending, the stress distribution across any cross-section of the beam is:

Explanation:

Stress Distribution in Pure Bending

When a beam is subjected to pure bending, the stress distribution across any cross-section of the beam is characterized by the following properties:

• Zero stress at the neutral axis because at this axis, there is no elongation or compression.

• Stress increases linearly from the neutral axis towards the outer fibers of the beam.

Analyzing the Given Options

1. "Zero at the neutral axis and increases linearly towards the outer fibers." (Correct Answer)

   • This statement accurately describes the stress distribution in a beam under pure bending.

2. "Higher at the neutral axis and decreases towards the top and bottom surfaces." (Incorrect)

   • Stress is actually zero at the neutral axis and increases linearly towards the outer fibers, not the other way around.

3. "Uniformly distributed across the entire section." (Incorrect)

   • In pure bending, the stress distribution is not uniform but varies linearly from zero at the neutral axis to a maximum at the outer fibers.

4. "Non-existent, as pure bending does not produce stress in the material." (Incorrect)

   • Pure bending does produce stress in the material, with the stress distribution being linear from the neutral axis to the outer fibers.