Calculating 'Effective' Shore Hardness

[rfdesign1]

A piece of rubber the size of 4 stacked quarters is needed for shock/vibration protection of electronics. It has been determined for the application that a Shore 'A' hardness of 35-40 works best. Due to mass constraints, the rubber is too heavy.

Is there a method to calculate the EFFECTIVE Shore 'A' hardness of a perforated piece of rubber that has a higher Shore 'A' hardness - with the intent that it's overall mass is acceptable due to the perforations? Assume the electronics circuit is the size of a quarter and presses flat against the rubber surface. For example, if there was a very simple linear relationship, then Shore A hardness 80 material with 50% of its volume removed with holes would yield an effective Shore 'A' of 40 for this application.

Let me know if there is a better metric for the rubber compression characteristic I am trying to control.

Thank you,
Dave

 

[GrahamBennett]

A rubber with a hardness of 80 Shore A with 50% of its volume removed will still be an 80 Shore A hardness rubber Dave.

A simple formula based on 100 parts of natural rubber that will give a cured hardness in the region of 35-40 Shore A would contain the following:
5phr N660 carbon black (this is just for colouring the rubber)
50phr calcium carbonate
20phr process oil
5phr zinc oxide
1phr stearic acid
1phr TMQ
2phr sulfur
1phr TBBS

 

[Compositepro]

Shore A is an empirical test somewhat related to compression modulus. You should be looking at DMA test data, which will tell you a storage modulus and a loss modulus. The storage modulus is sort-of the stiffness of the rubber and related to Shore hardness. For damping it is the loss modulus that is important. Loss modulus is a measure of energy lost through viscous effects.

 

[rfdesign1]

Yes, looks like DMA data is what I need. Are there test facilities that can test a material for me to determine the storage vs loss modulus? How should I search for them?

 

[GrahamBennett]

Rubber Consultants in the UK has the capability to run this test for you and make the parts.