Thermal Stresses And Strain in Hindi || Thermal Stress kya hoti hai

Summary

The video covers the concept of thermal stresses and thermal strain, explaining how materials expand when heated and contract when cooled. It discusses free expansion, where no stress occurs, and compares it to situations where expansion is restricted, leading to compressive or tensile stresses. The speaker uses relatable examples, like family dynamics and railway tracks, to explain the effects of thermal changes on material stress. The video concludes by explaining how these stresses can be calculated using material properties like the coefficient of thermal expansion and Young's modulus.

Takeaways

• 🌡️ Thermal stress and strain are caused by changes in temperature that affect a material's expansion or contraction.
• 📏 A material expands when the temperature rises, and contracts when the temperature falls.
• 💡 Free expansion of materials under temperature change does not induce stress unless their expansion is restricted.
• ✋ When a material's expansion is restricted, compressive stress is induced, resisting the material's attempt to expand.
• 🛠️ Tensile stress occurs when the contraction of a material is restricted under falling temperature, preventing it from shrinking.
• 🚂 Railways leave gaps between rails to prevent thermal stress during temperature changes, avoiding damage to the tracks.
• 📐 Thermal expansion is proportional to the change in temperature and the length of the material.
• 🔧 Thermal strain is defined as the change in length (delta L) divided by the original length (L).
• 💪 The formula for thermal stress is derived by multiplying thermal strain with Young's modulus (E).
• 📊 Partial restriction of expansion allows some free expansion, reducing overall thermal stress in the material.

Q & A

What happens to a material's length when its temperature increases?

When the temperature of a material increases, the material expands, resulting in an increase in its length. This phenomenon occurs because the material's particles gain energy and move apart, causing the expansion.

What is free expansion in the context of thermal expansion?

Free expansion occurs when a material is allowed to expand without any restriction as the temperature increases. In this case, no stress is generated in the material because it can expand freely.

What happens if the expansion of a material is restricted?

If the expansion of a material is restricted, it leads to the generation of compressive stress. The material tries to expand outward, but the restriction prevents it, causing internal forces to develop that result in compressive stress.

How does compressive stress occur in materials due to thermal expansion?

Compressive stress occurs when a material is prevented from expanding freely due to a rise in temperature. The restriction causes the material to develop inward forces, leading to compressive stress.

What example is used in the transcript to explain free expansion?

The transcript uses the example of children in English families, where they are allowed to explore and grow freely without restrictions. This example is compared to the free expansion of materials, where no stress is generated.

What analogy is used to explain compressive stress in the transcript?

The analogy used for compressive stress is how parents in some cultures restrict their children's freedom as they grow, leading to frustration. This is compared to a material being restricted from expanding, which causes compressive stress.

Why do railway lines have gaps between them?

Railway lines have gaps to allow for the expansion of the metal due to temperature changes. If the expansion is restricted without gaps, the rails can push against each other, causing bending or breakage due to thermal stresses.

What happens when a material's temperature decreases after being restricted?

When a material's temperature decreases, it tends to contract. However, if the material is restricted from contracting, tensile stress develops as the material is pulled outward.

How is thermal strain related to temperature change?

Thermal strain is the change in length of a material due to a change in temperature. It depends on the material's coefficient of thermal expansion (alpha), the original length of the material, and the temperature change (ΔT).

How can thermal stress be calculated from thermal strain?

Thermal stress can be calculated by multiplying the thermal strain by Young's modulus (E) of the material. The formula is: Thermal stress = E × Thermal strain.