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A copper rod of square cross-section is fixed between two rigid supports and over which a steel rod of square cross-section is simply placed. If the temperature of the whole assembly is raised by T °C, the stresses in steel and copper respectively are 

A copper rod of square cross-section is fixed between two rigid supports and over which a steel rod of square cross-section is simply placed. If the temperature of the whole assembly is raised by T °C, the stresses in steel and copper respectively are  Correct Answer zero and compressive

Concept:

Thermal Stress: This kind of stresses are induced in the material when its temperature is changed but the material is unable to accommodate its change in dimensions due to constraints. As long as the material is free to move, the material can expand or contract freely without generating thermal stresses. When temperate of the material is increased, the constraints exert a compressive stress on the material. The opposite happens while cooling i.e. the stress generated on the material will be tensile.

Now for this case,

  1. The copper rod is fixed between two rigid supports, it means it is unable to expand. So, when the temperature is raised compressive stress is generated in the copper rod.
  2. On the other hand the steel is placed freely, it means it can expand freely without any constraints. So, when the temperature is raised there will be no thermal stress generation in steel rod.

 

Note: This is not a case of composite bar. 

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