Cantilever with end load — location of failure under increasing load: When a vertical cantilever beam carries a load at its free end, where does failure initiate as the load is increased?

Difficulty: Easy

Correct Answer: at the fixed end

Explanation:

Introduction:Bending failure typically initiates where bending moment is maximum. For a cantilever with an end load, recognizing the bending moment distribution is key.Given Data / Assumptions:

  • Cantilever of length l; point load at the free end.
  • Linear elastic behavior up to failure.

Concept / Approach:Maximum bending moment occurs at the fixed support for a cantilever with end load. Extreme fiber stress is largest there, so yielding/crack initiation starts at the fixed end section.Step-by-Step Solution:

Shear diagram: constant along span; bending moment varies linearly from 0 at free end to Pl at fixed endMaximum σ_bending at fixed end: σ = Mc/ITherefore, failure initiates at the fixed end

Verification / Alternative check:Comparative check of stress magnitudes along the beam confirms the fixed section is critical.Why Other Options Are Wrong:

  • Free end / middle / 2l/3: bending moment is smaller away from the fixed support.
  • Uniformly along the span: bending stresses are not uniform.

Common Pitfalls:Confusing maximum deflection (free end) with maximum bending stress (fixed end).Final Answer:

at the fixed end

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