Is There a Connection Between Young's Modulus and Crystal Structure?

[RichieTU]

Hello guys,

does anyone know if there is a specific relationship between the modulus of elasticity and crystal structure/microstructure? I know that YM is basically derived from the chemical bonding, but how about the other two? As much as I know it should be not affected by the microstructural features in general, and it has different values in different measurements depending on direction on a crystal. Anything more specific than that?

 

[Astronuc]

Young's modulus and elastic modulus refer to the same property.
https://en.wikipedia.org/wiki/Young's_modulus

Is one interested in metals/alloys, or materials in general?

 

[RichieTU]

Materials in general.

 

[Astronuc]

Here is a discussion regarding elastic properties/constants of metals and alloys.
http://www.nist.gov/data/PDFfiles/jpcrd34.pdf

For other materials, like polymers, ceramics, glasses, . . . ., there will be different dependencies.

For metals/alloys, it largely depends on the elements (atomic bond strength) involved, crystal lattice, dislocation density, grain size (in polycrystalline materials). One will find considerable variability in reported values and dependencies for E and G, for example.

Many introductory textbooks on materials science and engineering should have some discussion on the subject.

 

[RichieTU]

Actually there is no standard relationship between YM and crystal structure/microstructure anywhere. There are occasions of alloys where it is affected by some microstructural processes but in a very small degree, so there is no general conncetion whatsoever. It is almost entirely dependent on the chemical bonding.
The same thing does not apply for other properties though, like yield strength which can be affected in a high level by both crystal structure and microstructure.

 

[Haseeb Shahdin]

Youngs Modulus could be said to be pretty much inherent property, but microstructures should also effect the Young's modulus just as in case of fine and coarse grain size. The finer ones will resist movement of dislocations more then the coarse microstructures and hence will have a higher yield strength.

 

[Mapes]

microstructures should also effect the Young's modulus just as in case of fine and coarse grain size

The grain size has essentially no influence on a material's Young's modulus, which describes the resistance to small amounts of stretching of the atomic bonds. Young's modulus is not yield strength. http://www.civilengineeringhandbook.tk/structural-steel/images/7742_27_6.png an example of how the stress-strain diagram changes with cold working, for example. The grain size decreases and the dislocation density increases, but the slope of the elastic region (i.e., the Young's modulus) remains unchanged.

(Also note that this thread is almost a year old.)

 

[Kevin McHugh]

Actually there is no standard relationship between YM and crystal structure/microstructure anywhere. There are occasions of alloys where it is affected by some microstructural processes but in a very small degree, so there is no general conncetion whatsoever. It is almost entirely dependent on the chemical bonding.
The same thing does not apply for other properties though, like yield strength which can be affected in a high level by both crystal structure and microstructure.

Actually, there is a relationship between elasticity and crystallinity in elastomers. Elastomers exist in an amorphous state with the polymer chains randomly coiled. If the material is subject to a stress by elongation, the polymer chains line up to form crystalline domains. These crystalline domains form spherulites which is exothermic. When the polymers chains relax, they resume their random coil configuration (endothermic). So there is a relationship between crystallinity and elasticity, but it is limited to the behavior of the elastic material.