The GATE Grind

GATE 2019 ME (ME2) – Question 18

Machine Design · Fatigue strength and S-N diagram · 1 mark · Multiple choice

The endurance limit of a beam under pure bending decreases with which combination?

  1. Decreased surface roughness and decreased beam size
  2. Increased surface roughness and decreased beam size
  3. Increased surface roughness and increased beam size
  4. Decreased surface roughness and increased beam size

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Correct answer: (C) Increased surface roughness and increased beam size

Explanation

A rougher surface increases local stress concentrations and promotes fatigue-crack initiation. A larger stressed volume also lowers endurance through the size effect. Thus increasing both roughness and size reduces the endurance limit: **C**.