×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Calculating 'Effective' Shore Hardness

## Calculating 'Effective' Shore Hardness

(OP)
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

### RE: Calculating 'Effective' Shore Hardness

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

### RE: Calculating 'Effective' Shore Hardness

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.

### RE: Calculating 'Effective' Shore Hardness

(OP)
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?

### RE: Calculating 'Effective' Shore Hardness

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

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!