Question

(Materials Testing Results)

Q: The 30% rubber group reported Rockwell numbers for fresh 48 hour and old as 12.5,21.5, and 88.5. How do you explain these results?

Answer 1

A higher Rockwell number means hardness of that material is quite high. Here, we see a great increse in hardness after 48 hours. Well then it might be a case of age hardening. If we will make a composite of duralumin (aluminium and copper alloy with 5.5% of copper) and rubber, where rubber can work as a binding agent (due to its better binding capability) and alloy as fiber. Duralumin gets hardened as time increses. So, I can say that given rubber is coupled with duralumin and has been through heat treatment. It has been tested several time having some hours of gap which leads to increse in its hardenability. A higher Rockwell number can give you higher haredenability but on the same time it can become brittle also ( it doesn't matter whether it is rubber or anything). In age hardening case hardenability increases due to formation of precipitates (in duralumin case Al2CU precipitate is formed) which create obstacles in movement of dislocation and hence increse the strength.