Shear modulus as a funtion of temperature

[SidVicious]

Why does the shear modulus of a metal decrease with increasing temperature, on an atomic scale?
Is it something to do with electrons gaining more energy allowing "layers" to slide around more easily??

 

[alxm]

Well, more to do with the nuclei gaining more energy. That is to say, the atoms are moving around more.
To give a simple, very generalized answer, you could simply think of it this way:
Energetically, you have to overcome an energy barrier to get the planes to start gliding. If the thing is warmer, it has more energy, so it takes less energy to cross over the barrier.
In terms of the positions of the atoms, you have to move them from the equilibrium position to the (higher energy) position where the 'gliding' starts.If the thing is warmer, the atoms are moving more and so a lot of them are already closer to the point they need to be at for 'gliding' to begin.

 

[charng]

Yes, you are correct. The shear modulus is a measure of a material's resistance to shear stress, which is the force applied parallel to the surface of the material. On an atomic scale, the atoms in a metal are arranged in a regular lattice structure. When a shear stress is applied, the atoms will move relative to each other, causing the material to deform.

At low temperatures, the atoms have less thermal energy and are more tightly bound to their positions in the lattice. This makes it more difficult for the layers of atoms to slide past each other, resulting in a higher shear modulus.

As temperature increases, the atoms gain more thermal energy and are able to vibrate and move more freely. This makes it easier for the layers of atoms to slide past each other, resulting in a decrease in shear modulus.

Additionally, at higher temperatures, the electrons in the metal gain more thermal energy and can move more easily within the lattice. This creates more disorder and reduces the cohesive forces between the atoms, further contributing to the decrease in shear modulus.

Overall, the decrease in shear modulus with increasing temperature is a result of the increase in thermal energy, which allows for greater atomic movement and reduced cohesion between atoms in the lattice.