In a composite system subjected to a temperature rise, with its ends constrained to remain together, the component with the lower coefficient of linear expansion will experience:
Try it first: pick an option, then read the explanation.
Correct answer: A. Tensile stress
Asked in SSC JE 03/03/2017 (Evening)
Detailed Explanation
If two bars are joined at their ends and heated, they must end up with the same length. Each bar wants to expand by a different amount.
Why “Tensile stress” Is Correct
The bar with the higher α wants to expand more but is held back, so it goes into compression. The bar with the lower α is dragged longer than it would freely expand, so it goes into tension. The forces are equal and opposite.
| Situation | Stress |
|---|---|
| Bar fully restrained, temperature change ΔT | σ = EαΔT (compressive on heating, tensile on cooling) |
| Composite bar heated (ends held together) | Material with higher α → compression; lower α → tension |
| Composite bar cooled | Higher α → tension; lower α → compression |
Why the Other Options Are Wrong
- B. Compressive stress: Compression is in the component with the higher α.
- C. Tensile or compressive stress depending on the loading: With heating only, the sign is fixed by the α values.
- D. Zero stress: Different α values with joined ends always cause stress.
Key Point
Heating a composite bar: lower α → tension, higher α → compression.
Key Concepts for Students
- Cooling reverses the signs.
- Force equilibrium: σ₁A₁ = σ₂A₂.
- Compatibility: final lengths are equal.
Practice more: this is question 17 in Stress and Strain MCQs – Part 2. Try the whole set and check every answer instantly.