Mechanical Engineering - Strength of Materials - Discussion

If temperature decreases then thermal tensile stresses induced.

No stress will devloped, If the body is free to expand or contract it will do not developed stress.

If the bar is fixed at both ends then it will develop tensile stress.

We thick analytically then we found that there is no resistance in opposite of contraction. So there is no stress.

If it is constrained, when we cool the bar it tends to shrink which develops tensile stress inside the bar.

Similarly, when we heat the bar it tends to expand and due to constraint compressive stresses are developed.

Tensile is fixed both the end.

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

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

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

There is No restriction, No stresses.

Here answer should be: no stress.

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