Mechanical Engineering - Strength of Materials - Discussion

Actually, first clear that, stress means an internal pressure which resists the external deformation.

After that whenever anybody is cooled it undergoes shrinkage that means externally compressive force is subjected therefore to resist them internally pressure developed is nothing but tensile stress.

Stress=load/area and is independent of temperature so no stress will develop.

Due to cooling, the metal will shrink. To keep herself in original shape metal will develop internal resistive force opposite to that shrinkage which will result in tensile stress.

In thermal analasys of stress if there is no restriction of strain no stresses are produced, in the given question they said that bar is cooled the bar is not in equbrlium then stress produced is zero.

No, stress is formed within the bar when cooled unless the bar is fixed.

Here answer should be: no stress.

But, if the bar is made of steel then, it should be: tensile stress.

There is No restriction, No stresses.

The answer to this question depends upon the past temperature of the bar. The formula for thermal stress is

(σ)thermal = (Eα . dT).
dT = Final Temp - Initial Temp.

So if the initial temperature of the bar was below -5° (like -10°), then -5° will obviously be considered as a rise in the temperature and therefore it will result into a compressive stress(positive thermal strain, expansion of the bar) as the difference between the temperatures will be positive. If the initial temperature was greater than -5° (like +10°), then cooling it down to -5° will result into a negative value of temperature difference and generate a tensile stress(negative thermal strain, contraction of the bar) in the bar.

Now, as the word "cooled to -5° is written in the question, it shows that the initial temp was more than -5°. Hence the stress will be tensile. The Answer is [C]. I assume that the bar is held at the ends from expanding. If not, then the answer

Tensile stress is the correct answer but the body should be restricted to change the shape because of cooling.

No stresses are developed as there is no restriction for material flow or shrinkage, stresses are induced only when there is a restriction.