Enginerd (Mech) help

Do you store your car on blocks for fear of the suspension sagging?

The unfortunate answer is that it depends on the spring and how it is used. The best answer would come from the manufacturer of the product. A cheaper spring that is pushed close to the yield point can certainly lose strength quickly. A better spring that is pushed only to a fraction of the yield point will show negligible losses. I'm guessing a lot of the gun related superstitions came from a time when metallurgy wasn't what it was today.

Flexing any metal will basically chew into it's fatigue life. Fatigue life is relatively predictable and it can be designed into a product. Bridges are designed to last a very long time, the trunk spring on a '78 gremlin not so much. In theory a piece of steel can be designed to have an infinite fatigue life but it is not always practical.

I would think that operating a spring should affect the strength of the spring more than having a load over a long period of time. But things like changes in temperature could affect a loaded spring causing strain cycles without motion.

Cyclic loading of the spring will eventually weaken it. Depending upon the material chosen and the load it is subjected to the spring may never fail. Of course, failure will be based upon material properties and the operating environment as well.

Theoretically pausing during the cycle should not weaken the spring as long as it is not pushed beyond its elastic limit. Again, that is subject to the stipulations of loading, material properties, and operating environment.

Westy said:

Do you store your car on blocks for fear of the suspension sagging?

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My girlfriend's father showed me a picture of a house he drove by who's owner had put their car up on blocks to prevent sagging. Too bad they put the blocks under the wheels....

MikeD said:

OK, please, someone with the actual education, assist me!

-Cycling a spring over and over will eventually weaken it, right? (And/or what will weaken a spring, if it's only certain things that will cause it?)

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Yes its called fatigue. When we write strength margins for components we base them on a 10^x number of cycles during its lifetime. 100,000, 1,000,000 etc. Once that is known there is a percent knockdown for the ultimate strength allowable of the material. And easy example is 100,000 pounds/square inch ultimate stress would be knocked down by 50% to 50,000 at 1 million cycles. So that would mean if you want it to survive 1 million cycles you should not load it over 50% of its ultimate stress.

With this method you're assuming its already weaker from the start in order to prevent it failing prematurely do to higher repeated loads.

MikeD said:

-Will pausing somewhere in this cycle with the spring compressed, for an indefinite amount of time, continually weaken the spring as it sits static? Or, conversely, will only repeated cycling weaken the spring?

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There is creep that occurs in all structures and permanent strain. Creep will make the displacement change over time. When we preload fasteners we assume a 5% loss of preload due to relaxation/creep in materials.

Permanent strain/deformation (or residual strain) will depend on how far past the material's elastic range you have gone during compression/tension loading. If you stay well below the elastic limit of the material you have nothing to worry about. *Keep in mind most materials are still considered in their elastic range even after a 2% deformation has occurred.

Okay, a lot the stuff above I have no idea what you guys are talking about, but I do have a question. I was told when I store my skis for the winter I should back the bindings all the way down. Thus releasing all of the tension on the spring. The reason I was told was that if they stayed tensioned year after year the din setting number will not be an accurate measurement of the binding's tension. BS or not?

mogulskr said:

Okay, a lot the stuff above I have no idea what you guys are talking about, but I do have a question. I was told when I store my skis for the winter I should back the bindings all the way down. Thus releasing all of the tension on the spring. The reason I was told was that if they stayed tensioned year after year the din setting number will not be an accurate measurement of the binding's tension. BS or not?

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I don't know anything about ski bindings (15 year snowboarder here).

Ithnu said:

I don't know anything about ski bindings (15 year snowboarder here).

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Basically you tension a spring in the front and rear to hold your boot in the binding. The more tension the harder to release. So if the spring is under constant tension, over time would the spring not be as tense at the same setting year over year?

mogulskr said:

okay, a lot the stuff above i have no idea what you guys are talking about, but i do have a question. I was told when i store my skis for the winter i should back the bindings all the way down. Thus releasing all of the tension on the spring. The reason i was told was that if they stayed tensioned year after year the din setting number will not be an accurate measurement of the binding's tension. Bs or not?

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bs.

345

mogulskr said:

Okay, a lot the stuff above I have no idea what you guys are talking about, but I do have a question. I was told when I store my skis for the winter I should back the bindings all the way down. Thus releasing all of the tension on the spring. The reason I was told was that if they stayed tensioned year after year the din setting number will not be an accurate measurement of the binding's tension. BS or not?

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If its in tension and you pull it past the elastic limit there will be permanent deformation. If you leave it at this high tension point it will creep a bit and give you a bit more permanent deformation so your tension settings may not be as accurate. However you're not cycling the spring so I'd imagine the affect is minimal but it is still present. How much? It would vary on every set of bindings I'd imagine.

When you put your boot in does it compress the spring before it goes into tension? If so a high tension setting would cycle the spring above its elastic limit pretty often and would be keeping the spring above this limit every time your boot is in there. I think this would have more effect in terms of fatigue than the additional creep present by leaving it in tension over the summer.

Ithnu said:

If its in tension and you pull it past the elastic limit there will be permanent deformation. If you leave it at this high tension point it will creep a bit and give you a bit more permanent deformation so your tension settings may not be as accurate. However you're not cycling the spring so I'd imagine the affect is minimal but it is still present. How much? It would vary on every set of bindings I'd imagine.

When you put your boot in does it compress the spring before it goes into tension? If so a high tension setting would cycle the spring above its elastic limit pretty often and would be keeping the spring above this limit every time your boot is in there. I think this would have more effect in terms of fatigue than the additional creep present by leaving it in tension over the summer.

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Translation: I have no idea.

mogulskr said:

Basically you tension a spring in the front and rear to hold your boot in the binding. The more tension the harder to release. So if the spring is under constant tension, over time would the spring not be as tense at the same setting year over year?

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Basically you could experience some creep......but I doubt it would be noticeable from one season to another. Maybe if you left them for like 10 years.....like say my skis for instance......

Only a poorly designed spring will markedly weaken or deform if left in a loaded condition which it was designed to endure. If you've got a museum-piece gun or camera which you will retire to a museum when you finish with it, unload the springs. On a long enough time line everything will be affected.
Your bindings, not so much. Have them checked every decade, but I doubt they will lose tension as fast as the ligaments in your knees. The lighter release may be a welcome change.

mogulskr said:

Okay, a lot the stuff above I have no idea what you guys are talking about, but I do have a question. I was told when I store my skis for the winter I should back the bindings all the way down. Thus releasing all of the tension on the spring. The reason I was told was that if they stayed tensioned year after year the din setting number will not be an accurate measurement of the binding's tension. BS or not?

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bs. i have never heard of such a thing in all the years i've skied. keeping your boots buckled in the off season yes, but nothing about screwing with the bindings.

Taking the tension off of a spring is never a bad thing. If your bindings are at 8 all summer long for no reason, it's doing more harm that good....albeit an infinitesimal amount of harm. But backing the tension off at the end of the season and then putting them back up to 8 when the season comes again.....there is certainly no harm in that. A relaxed spring will last longer than one that is under load. It's the definition of "longer" that is up for debate.

maddog17 said:

<snip> keeping your boots buckled in the off season yes,

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No.....

A properly and ideally designed spring will settle to a specific point during its normal use, and be capable of infinite life within these parameters. Most springs are not designed this way though.