# Stress Strain & Thermal Stress (Stress and Strain Part-1)

##### It is denoted by σ

For e.g. spring is placed on your hand and you press it or stretches it, compression or tensile forces generate.

##### Strain: When a body is subjected to an external force. Then there will be change in the length of the body. So the strain is defined as

When F force is being applied to a body of length “l” and width “b” .

δl is linear change and δb is lateral change.

## Thermal Stresses

Whenever there is a change in the temperature of the material it either expands or contracts.

Findings have shown that Change in length is directly proportional to change in temperature. Also, change in length is proportional to the Initial length.

#### Now we will see general cases:

Case 1. If a bar is fixed at one end only.

#### δl = α l ΔT

##### and the stress is zero, σ = 0

Case 2. If the bar is fixed at both ends and the walls are exerting the same amount of force in such a way that it would expand same amount if it was free.

Here in this case change in length is stopped by the Force applied by the walls. So change in length due to thermal expansion will be equal to change in length due to resisting force.

Case 3. If the bar is fixed at one end and the other wall is at some distance which is δ.

### Now two conditions can occur:

#### a)

In this case σ = 0, because expansion from thermal stresses is less than the gap between the walls. So if the body is not reaching another wall, there won’t be any resisting force.

#### b)

In this case thermal expansion will be greater than δ, So wall be provide resisting force & Stress will be

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