Which one of the following statements is NOT correct?

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UPSC ESE (Prelims) Civil Engineering 19 Feb 2023 Official Paper
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  1. For structural steel, the rupture strength is higher than the ultimate strength.
  2. Yield stress is the lowest stress at which extension of the test piece increases without further increase in load.
  3. The ultimate strength is commonly taken as the maximum stress of the material.
  4. Ultimate strength is the ratio of maximum load to the original cross sectional area.

Answer (Detailed Solution Below)

Option 1 : For structural steel, the rupture strength is higher than the ultimate strength.
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Detailed Solution

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Explanation:

Mild steel stress-strain curve:

 

A → Limit of proportionality point

B → Elastic limit point

C' → Upper yield point

C → Lower yield point

D → Strain hardening start point

E → Ultimate strength point or maximum stress point

F → Fracture point (rupture strength)

  • Rupture strength; It is the stress corresponding to the failure point F of the stress-strain curve.
  • Rupture strength is less than ultimate strength.
  • Ultimate strength is the maximum stress of the material.
  • Ultimate strength is the ratio of maximum load (ultimate load) to the original cross-sectional area.
  • Yield stress is the lowest stress at which the extension of the test piece increases without a further increase in load.

​Statement (1) is the incorrect statement about structural steel. Hence option (1) is the correct answer.

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