The hoop stress induced in a thin cylinder by winding it with wire under tension will be:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 02/03/2017 (Morning)
Detailed Explanation
To make a thin cylinder carry more pressure, it can be wound tightly with steel wire under tension. This puts a prestress into the cylinder before any internal pressure is applied.
Why “Compressive” Is Correct
The stretched wire tries to shorten and grips the cylinder like a tight band, pressing its wall inward. The wall therefore develops compressive hoop stress (and the wire is in tension). When internal pressure is later applied, the tensile hoop stress it causes first cancels this compression, so the cylinder can safely take a higher pressure.
Why the Other Options Are Wrong
- B. Tensile: The wire is in tension; the cylinder wall it squeezes is in compression.
- C. Shear: Winding produces a direct (normal) hoop stress, not shear.
- D. Zero: The tight wire does produce stress in the cylinder.
Key Point
Wire winding: wire in tension, cylinder wall in initial hoop compression.
Key Concepts for Students
- Prestressed concrete pipes and tanks use the same idea.
- Final hoop stress = initial compression + tension due to pressure.
- Gun barrels are strengthened similarly by shrink-fitting (compound cylinders).
Practice more: this is question 3 in Thin Cylindrical and Spherical Shells MCQs – Part 1. Try the whole set and check every answer instantly.