How to convert Durometer Reading to a Stiffness for modelling in Nastran
How to convert Durometer Reading to a Stiffness for modelling in Nastran
(OP)
Hello,
Hoping someone can help me out here.
First the scenario:
We have a test set-up that I have to model in Nastran. As an oversimplification of the set-up, think of a simply supported beam on both ends. The supports are made of steel blocks topped with a 1/4" thick silicon rubber so that the "beam" does not get localized damage when a force is applied at the center.
I would like to model this in Nastran, but would like to include the stiffness of the rubber material so that I can get more realistic deflections and internal loading.
My plan is to introduce a GAP element between the beam, and the support/constraint with an initial GAP of 1/8" (since the rubber will never be fully compressed during loading. However, I have to give this GAP a open stiffness of the rubber material. The closed stiffness will be something high like 10e7.
The only information I have of this rubber material is that it has a durometer hardness of 67A. Can someone tell me (hopefully with insudtry references) how I can convert this durometer reading to an equivalent stiffness that I can use in my models? It doesn't have to be highly precise, but perhaps an average stiffness will work since I know rubber stiffness changes as the amount of force is being applied.
Keep in mind that I'm doing this to reduce the conservatism in my analysis. I could forego modelling the rubber altogether and get high stresses and larger deflections if I assume a hard constraint.
Thanks in advance for your insight and advice.
Hoping someone can help me out here.
First the scenario:
We have a test set-up that I have to model in Nastran. As an oversimplification of the set-up, think of a simply supported beam on both ends. The supports are made of steel blocks topped with a 1/4" thick silicon rubber so that the "beam" does not get localized damage when a force is applied at the center.
I would like to model this in Nastran, but would like to include the stiffness of the rubber material so that I can get more realistic deflections and internal loading.
My plan is to introduce a GAP element between the beam, and the support/constraint with an initial GAP of 1/8" (since the rubber will never be fully compressed during loading. However, I have to give this GAP a open stiffness of the rubber material. The closed stiffness will be something high like 10e7.
The only information I have of this rubber material is that it has a durometer hardness of 67A. Can someone tell me (hopefully with insudtry references) how I can convert this durometer reading to an equivalent stiffness that I can use in my models? It doesn't have to be highly precise, but perhaps an average stiffness will work since I know rubber stiffness changes as the amount of force is being applied.
Keep in mind that I'm doing this to reduce the conservatism in my analysis. I could forego modelling the rubber altogether and get high stresses and larger deflections if I assume a hard constraint.
Thanks in advance for your insight and advice.






RE: How to convert Durometer Reading to a Stiffness for modelling in Nastran
Cheers
Greg Locock
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RE: How to convert Durometer Reading to a Stiffness for modelling in Nastran
My experience is that bonded rubber items produce very high shear loads when compressed if they cannot bend or otherwise distort.
Google result:
https://www.3dvision.com/blog/entry/2011/07/14/con... and
https://www.3dvision.com/blog/entry/2016/04/01/sho...
RE: How to convert Durometer Reading to a Stiffness for modelling in Nastran
Nastran stiffness is not given in units of pressures. It is in units of lbs/in or N/mm. So my follow-up question would be if I only had the durometer hardness of 67A ... I can calculate the Young's Modulus using the equations that google can give me ... but how do I convert that to a stiffness?
The rubber is essentially laying on top of a steel block ... all being held together with good ole duct tape all around.
RE: How to convert Durometer Reading to a Stiffness for modelling in Nastran
BA
RE: How to convert Durometer Reading to a Stiffness for modelling in Nastran
It is from From this page, which is pretty interesting but does not mention silicon rubber that I coul see.
http://www.moldeddimensions.com/urethanes-in-compr...
RE: How to convert Durometer Reading to a Stiffness for modelling in Nastran