Modulus of elasticity (Young's modulus) for mild steel — choose the closest standard value. Give your answer in kN/mm^2 (note: 1 kN/mm^2 = 1 GPa).
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A10 kN/mm2
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B80 kN/mm2
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C100 kN/mm2
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D210 kN/mm2
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E25 kN/mm2
Answer
Correct Answer: 210 kN/mm2
Explanation
Introduction:Mild steel (low-carbon steel) is a standard structural material. This question tests recall of its elastic stiffness, commonly used in beam, column, shaft, and plate calculations in civil and mechanical engineering.Given Data / Assumptions:
- Material: mild (low-carbon) steel.
- Small-strain, linear-elastic range.
- Units: kN/mm^2 where 1 kN/mm^2 = 1 GPa.
Concept / Approach:Young's modulus E links normal stress and normal strain by Hooke's law: σ = Eε. For steels, E is nearly constant across grades and heat treatments within engineering accuracy, typically around 200 to 210 GPa (i.e., 200–210 kN/mm^2).Step-by-Step Solution:
Recognize standard value: E_steel ≈ 200–210 GPaConvert understanding of units: 1 GPa = 1 kN/mm^2Select the closest choice: 210 kN/mm^2Verification / Alternative check:Handbooks and codes often tabulate E_steel = 2.010^5 to 2.1*10^5 N/mm^2, which equals 200–210 kN/mm^2, confirming the chosen answer.Why Other Options Are Wrong:
- 10, 25, 80, 100 kN/mm^2: Far lower than accepted values for steel; such stiffnesses are more typical of polymers (very low) or some non-ferrous alloys (still higher than listed low values).
Common Pitfalls:Confusing strength (e.g., fy) with stiffness (E); mixing up units such as MPa, GPa, and N/mm^2. Remember: E for steels is relatively invariant compared to strength grades.Final Answer:
210 kN/mm^2