Bending Stress in a Beam Cross-Section

Bending stress is a type of stress that occurs in a beam when an external load is applied to it, causing it to bend. The distribution of bending stress across the cross-section of the beam is not uniform. The bending stress is maximum at the extreme fibers of the beam and zero at the neutral axis.

1. Neutral Axis:
- The neutral axis is an imaginary line that divides the cross-section of the beam into two halves - the top half and the bottom half.
- It is the line at which the average stress is zero when the beam is subjected to bending.
- The neutral axis passes through the centroid (center of gravity) of the cross-section.

2. Extreme Fibers:
- The extreme fibers are located at the outermost edges of the cross-section, farthest from the neutral axis.
- These fibers experience the maximum stress when the beam is subjected to bending.

3. Bending Stress:
- Bending stress is caused by the moment of the external load acting on the beam.
- The formula to calculate the bending stress is given by: σ = (M * y) / I, where σ is the bending stress, M is the bending moment, y is the distance from the neutral axis to the point of interest, and I is the moment of inertia of the cross-section.
- As y increases (moving away from the neutral axis towards the extreme fibers), the bending stress increases.

Explanation of the Correct Answer:

The correct answer is option A - Zero, Maximum.

- At the neutral axis, the distance y is zero since it is the line where the average stress is zero. Therefore, according to the bending stress formula, the bending stress at the neutral axis is zero.
- At the extreme fibers, the distance y is maximum since it is the farthest point from the neutral axis. Therefore, according to the bending stress formula, the bending stress at the extreme fibers is maximum.

Hence, the bending stress at the neutral axis is zero, and the bending stress at the extreme fibers is maximum.