hardness vs compound vs Elastic modulus 1

[candychan]

Hi,I have a question on the relation of hardness and elastic modulus,I had ever got the idea from somewhere that the mechnical property of rubber is determined by the hardness,and now I am doubt about it.Do you agree the idea that same hardness with different compounds would share the same elastic modulus?

 

[orangepeel]

I believe that there are other postings here that discuss this, or the related question of correlating Shore A and Shore D hardness. In my opinion, there is a rough correlation between hardness, and elastic (initial Young's Modulus), but I would rather conduct some mechanical tests to be sure. Since rubber typically exhibits nonlinear elastic stress-strain behavior, you may need more than just a single value for elastic modulus.... depending on your application and accuracy needs.

 

[EddyIwantoro]

The same hardness will not has the same modulus for different compounds!! Fyi, the mechanical properties are FAR BEYOND than hardness and modulus.
There are secrets in rubbercompounding about how to improve the mechanical properties. Hardness and modulus are only two aspects in general.

Try ask this deep phenomenon about hardness and modulus (static and dynamic) to the rubber experts at

 

[EddyIwantoro]

The same hardness will not has the same modulus for different compounds!! Fyi, the mechanical properties are FAR BEYOND than hardness and modulus.
There are secrets in rubbercompounding about how to improve the mechanical properties. Hardness and modulus are only two aspects in general.

Try ask this deep phenomenon about hardness and modulus (static and dynamic) to the rubber experts at

http://groups.yahoo.com/group/rubbercompounding/

 

[Caliglueguy]

I understand that Hardness and modulus may not be able to relate mathematically, but intuitively believe that hardness is related to bulk modulus of a material. I would like other peoples opinions on this. Specifically, I do not believe you could have a material with a very low modulus, say 5000 psi, and a hardness of Shore D 90.

Thoughts?

 

[orangepeel]

For rubbers, what we call hardness is a measure of how deep an indenter is pressed into the rubber, given a certain force or energy... but when the indenter is removed, there is typically no permanent mark, as there would be for a metal. Hence, the hardness is a measure of elastic deformation vs load, much as the various forms of stiffness (Young's, shear, bulk modulii) are. In that sense, I believe that they are directly related. However, you also have to consider the degree of crosslinking, fillers, additives, chain branching, degree of polymerization, whether there is co-polymerization, and so on.... So I think that we can safely say there is a direct correlation, but that it is not well defined because of all the additional factors. For isotropic materials, we know that Young's Modulus and Shear modulus are related, using a Poisson's ratio, but are all rubbers isotropic? ..... in reality due to chain allignment, they are probably not, although we assume they are.

I would think that if you were to thoroughly search the work on this area, that some fairly good correlations between shore hardness and bulk modulsus, for example, within sub-groups of rubbers, that have well defined levels of crosslinking, branching, DP, low crystallinity, and so on, could be found.

try scirus.com for a search engine and good luck!

 

[Highspeed]

Try this

http://www.simritna.com/catalog/o-ring/98physics_rubber.htm

It gives you an idea of how complex it can be

 

[smanish]

I was also having the same problem and I think all the related issues like variations in crosslinking density, viscoelastic properties etc. have been dealt with in detail in a book by Alan N. Gent named " Engineering with Rubber".
The gist of the discussion is that the relation between shoreA and modulus properties is only approximate though valid in the range ShoreA 30-60