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urethane suspension bushings

urethane suspension bushings

urethane suspension bushings

(OP)
My Google-fu has come up short-

For an automotive suspension design, in a mostly street application:
What would be an acceptable loading for urethane bushings, such as these:
Link

Since it's not a bonded setup, it would strictly be compression against the projected area of the inner sleeve.
What kind of static psi loading would be reasonable?
(a pair of bushings will transmit spring loads to each hub.)

Or am I totally screwing up here?
The total vehicle is 2400 lbs, with about 1400 on this end.
(rear, driven, not supposed to steer)

Regards
Jay

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: urethane suspension bushings

OEM bushes are double bonded and sized (precompressed) for a good reason. However that doesn't answer your question. Yield strength for PU is say 7000 psi at 23 deg C, so guessing you've got 350 psi static load it should be ok, but I'd worry about creep.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: urethane suspension bushings

(OP)
Hi, Greg - thanks for the quick response.
Well, that's - interesting.
I get a projected area of ~ .84 in^2 (that's bolt diameter, not sleeve - assuming the outer edges of the sleeve aren't doing much)
Which would give a load at yield of ~5900 lbs per bushing, * two bushings.
Not a huge safety, with total load (3G bump at max cornering) calculated at ~ 4000 lbs.
- Why did you suggest 350 lbs? Massive safety factor?

Bushing failure will make things go wobbly, but should give lots of warning before anything can come apart.

I can fab this pretty easily - but it looks really hard to use a ball joint there.
If necessary, I could go with some other kind of bushings or bearings there.

Regards
Jay

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: urethane suspension bushings

I guessed 2 sq in of contact area on the pin and 700lbf static, didn't consider dynamic loads.

Failure will be noisy but not life threatening, SOP during testing is to remove all the rubber from all the suspension bushes and check that the thing is still drivable, and I've driven a few and they are.

If you can find a nice OEM part from a strut it'll last longer, you may need a double metal and push it into the welded tube.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: urethane suspension bushings

Kastalon quoted me a value of 4000psi for Shore 83A urethane rubber bonded to a substrate. They assume ~60degree stress distribution through the thickness. They have a very good technical manual which you could download from their website.

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