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SN Curve for Silicon Rubber

SN Curve for Silicon Rubber

Hello there engineering community.

I am trying to perform a fatigue analysis on a silicon rubber off/on switch using Solidworks 2017 Simulation Premium. Most of the materials in the database do not have associated fatigue curves. The silicon rubber material doesn't have one. Does anybody know if fatigue curves (or fatigue data) exists for rubber?


RE: SN Curve for Silicon Rubber

Tough one. Yes, fatigue data for rubber "exists", but it is unlikely to help you:

1. getting fatigue data for silicone rubber may be tough (you probably already know that) as it's relatively "newer" than other rubbers, and generally weaker in tension and thus not often used as a critically stressed item...
2. even if you find it, you need to know the material is a close match for yours (durometer of rubber, type and amount of fillers and/or reinforcements, type and degree of cure, type of load, frequency of loading, prior loading history, prior temperature history... all play significant parts in the fatigue strength/life of rubber, and those are just some of the relevant items)...
3. even when it's your own data for your own material, the fatigue data will show a lot of scatter, maybe double what you might expect from data for a cast metal alloy.

You might be able to find, with enough searching on Google scholar, some data/reports that will be in the ballpark relative to your material, and give you some general ideas of how to improve on fatigue life.

Good luck.

RE: SN Curve for Silicon Rubber

And silicone is not very damage tolerant, a nick or cut will greatly weaken it.
When we had flexing rubber parts we did notched tear tests on aged samples, and then stayed under 20% of the elongation value from the tests.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: SN Curve for Silicon Rubber

adp1215... a few observations, this subject.

Consistent fabrication processes + consistent rubber formulations + consistent quality inspections [including NDI of internal quality] are very important to initial base-line component quality.

Operational environments can be a wild-card for a durability analysis. Silicone rubbers tolerate exposure to various stress/strain, weather, thermal and chemical exposure environments to widely varying degrees [fairly good to extremely poor]. Fluorosilicone rubber compounds GENERALY do better than conventional silicone rubber compounds [molded parts and as 1 or 2-part RTV adhesive sealants] in most environments.

Fiber reinforced fluorosilicone rubber parts or thick coatings have a better degree of 'toughness' and environmental resistance than non-reinforced conventional silicone rubbers... when made with high quality control.

Any entrapped voids [or lack of cohesive continuity] within parts or coatings can be a hairy proposition to deal with [predict, analyze-for]. EXAMPLE. A reinforced silicone rubber insulation coating was applied to the Space Shuttle external tank [red-color seen on most ETs]. When the ET was fueled with LOX and LHX cryogenics, the rubber coating became hard as rock as the et structure contracted [up-to (-)6-inches in Dia]. Any air-entrapped in the coating voids was liquefied. After lift-off, as dynamic air friction heated the ET rubber insulation, these liquefied gas pockets were rapidly superheated causing the entrapped air-gas to explosively pressurize, blowing-off popcorn like chunks of the coating system. When these popcorn-size chunks spalled-off they often led to large-area insulation coating failures, which was aggravated by aerodynamic shear forces and ET aluminum structure re-expansion [aerodynamic heating + reducing atmospheric pressure]. NASA learned the hard-way that these voids had to be discovered by ultrasonic NDI... then repaired/eliminated each-one-at-a-time [void-cavities were opened/re-potted]... well before launch to ensure the ET coating system survived to orbit insertion.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", forum]

RE: SN Curve for Silicon Rubber

FYI... stumble-on, during other work/questions, this subject.

The following specification MAY/MAY-NOT provide useful info...

ASTM D813-07 Standard Test Method for Rubber Deterioration - Crack Growth

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", forum]

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