Young's modulus is a measure of the stiffness of a material. It is defined as the ratio of stress to strain within the elastic limit of a material. The elastic limit is the maximum stress that a material can withstand without undergoing permanent deformation.

Effect of temperature on Young's modulus:

1. Thermal Expansion:

When a material is heated, its atoms vibrate more rapidly, causing an increase in the distance between them. This results in thermal expansion of the material. As a result, the stiffness of the material decreases, and its Young's modulus decreases.

2. Change in Bond Energy:

The Young's modulus of a material is related to the bond energy between its atoms. At higher temperatures, the bond energy decreases, leading to a decrease in the Young's modulus.

3. Change in Crystal Structure:

Some materials undergo a change in crystal structure when they are heated. This change can result in a change in the Young's modulus of the material. For example, in some metals, the crystal structure changes from a face-centered cubic structure to a body-centered cubic structure at high temperatures. This change can result in a decrease in the Young's modulus.

4. Thermal Stress:

When a material is heated or cooled, its volume changes due to thermal expansion or contraction. If the material is constrained in some way, these volume changes can result in thermal stress. Thermal stress can lead to a decrease in the Young's modulus of the material.

Conclusion:

In general, the Young's modulus of most materials decreases with increasing temperature, primarily due to thermal expansion and a decrease in bond energy. However, there are some exceptions to this rule, such as certain polymers, where the Young's modulus increases with increasing temperature.