In the theory of pure bending of beams, the "Neutral Axis" of the cross-section is the layer where
- AThe bending stress is maximum.
- BThe bending stress is zero.Correct
- CThe shear stress is maximum.
- DThe tension is equal to the curvature.
Solution
Concept
Neutral Axis in Pure Bending
Step-by-step solution
1. Recall the bending equation M/I = σ/y = E/R, where σ is the bending stress and y is the distance from the neutral axis. 2. At the neutral axis layer, y = 0, which results in bending stress σ = 0. 3. Compare with the given options and select Option (b) as the correct choice.
Explanation
At the neutral axis of a beam subjected to bending, the longitudinal fibers experience no elongation or compression, meaning there is zero strain and consequently zero bending stress.
Common mistake
A common mistake is selecting Option A by confusing the neutral axis with the outer extreme fibers where bending stress reaches its maximum. Another frequent mistake is selecting Option C by confusing the bending stress distribution with the shear stress distribution, as maximum shear stress often occurs at the neutral axis, whereas bending stress at the neutral axis is zero.
Correct answer: B) The bending stress is zero.