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Leaf Spring Tech: Spring Stress

Discussion in 'The Garage' started by Triaged, Jun 5, 2003.

  1. Triaged

    Triaged 1/2 ton status

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    I just added a column for stress in a excel spreadsheat I made last summer.

    http://home.earthlink.net/~triaged/LeafSprings.xls

    You can use this to find out how much lift you will get from a set of springs (a bit more work than just putting the #'s in), Find the spring rate of those cool 57" f-150 springs (no one has got me the measurements yet /forums/images/graemlins/rolleyes.gif), you could even figure out where to put the bump stop to keep the springs from yielding when compressed.

    Have fun with it.
    If you have any sugestions I would like to hear them
    I would love to have some more info to put in the file...
    If you have the time (and a set of calipers/micrometer) I would love some more springs in the list.
     
  2. Triaged

    Triaged 1/2 ton status

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    What? No body liked my tech?
    I know I need more springs in there (as the only ones that are in there are the ones on my truck and in my backyard).
    I would think about putting in coil springs but they are much easier to find info on and for the most part can't yield (they go into coil bind before they yield).

    Do you guys want to see some real data on shackle angle influance on spring rate??
     
  3. Executioner

    Executioner 1/2 ton status

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    Cool,
    Just don't have the time now to try it out.
    Thanks for doing the 86209's
     
  4. Triaged

    Triaged 1/2 ton status

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    On alot of those springs I worked backwards. I could find info on # of leaves, free arch, and spring rate but not leaf thickness. They use the same equations to find the spring rate that they list so I just used that to find the thickness.
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    What measurement do you need on the 57's? Free arch on mine was 9" and loaded arch was about 1.5". The weight bias on my truck is damn close to 50/50 and it weighed 5700 lbs when I made those measurements.

    That's roughly 2800 lbs over the rear compressing 2 springs 7.5". My handy dandy calculator tells me the spring rate is roughly 186 lbs/inch./forums/images/graemlins/smile.gif

    If you want leaf thickness I can get you that tomorrow.

    rene
     
  6. Triaged

    Triaged 1/2 ton status

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    The most important is leaf thickness. It has to be very accurate because in the equation it gets cubed.

    If you have no pads in between the leaves I could do with a measurement (to about .005") of the whole pack thickness and the # of leaves. Also don't forget that you have to subtract the un-sprung weight from the truck to to find the spring rate.
     
  7. Triaged

    Triaged 1/2 ton status

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    Oh...almost forgot free arch is measured from the line between the spring eyes to the bottom of the leaf. Is that where you measured? It won't matter unless you are trying to figure out how much lift you will get or in compairing it to any of the ones I have already done.
     
  8. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I measured the arch the same way for loaded and free arch, but I do have about 700 lbs of unsprung weight so those 57's are considerably softer than 186 lbs/inch.

    I don't have calipers of any sort where my truck is...sorry. I do have slip pads on each spring so measuring the whole pack won't be accurate either.

    I'll see what I can come up with for you.

    Rene
     
  9. fr8train

    fr8train 1/2 ton status

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    Great article Dan!
     
  10. Triaged

    Triaged 1/2 ton status

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    So do your springs sit flat at ride height? If you get me the leaf thickness it would be easy to tell you where to put the bump stop...
     
  11. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    There is a slightly positive arch to them at ride height. I'll try and measure the thickness of the pack at the perch today.

    Rene
     
  12. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    [ QUOTE ]
    What? No body liked my tech?


    [/ QUOTE ]


    Dan,

    Maybe some people got lost (like me) in the last few columns


    Deflection (Huh?...Is this how much longer the eye-to-eye measurement gets when it flexes/flattens out?)

    Loaded Arch (I'm guessing this is what's left of "free arch" once you put the weight of the truck on it?)

    Stress KSI (Some kind of rating on when the spring is going to be over-stressed and can break?)



    I suspect that it's not the chart, it's the need for more understanding about HOW these values might be useful and how to apply them in some way to our vehicles.

    I think most of us know that a longer, flatter spring typically flexes better.....but what can we infer about spring who's free arch and loaded arch are dramatically different....and what will that Stress KSI column help me to know???

    Stuff like that is probably the "background info" that will help this chart to propel you to greatness!!! /forums/images/graemlins/grin.gif
     
  13. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    OK, main leaf is 9/32", and all the others are 1/4". That is as accurate as I could get. I don't have calipers anywhere near where my truck is at...

    Rene
     
  14. Triaged

    Triaged 1/2 ton status

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    Deflection:
    When you put the load in the column befor the spring will compress that much. This is used to find loaded arch from free arch.

    Loaded arch:
    How much arch there is to the spring with the weight from the load column on it.

    Stress:
    I really should have said more on this. 1 ksi is 1000 psi. You just end up with easier #'s to deal with. The yield strength of the spring steel is about 90 ksi (or 90,000 psi).

    There are a few good uses for the chart.

    1) Figure out where to put the bump stop.
    You want to set the bump stop so that the spring won't yield when you flex it out. Because of all of the other factors not included in the chart (like spring wrap...) you should aim for a # less than about 60 ksi for the stress (or a factor of saftey of 1.5). You then change the # in the load column untill the stress is about 60 ksi. Then look at the loaded arch. This is where you would want your bump stop to be. Flex out the truck untill the spring is arched to the correct ammount (remember this is the distance from a line from eye-to-eye to the bottom of the spring) and put your bump stop there.

    2)Find the ammount of lift you will get with some springs that were not made for your application (i.e. rear springs in front...).
    Find out what your SPRUNG WEIGHT is at the corner in question. Measure and input all the spring data. Measure the current loaded arch (with stock springs or whatever referance you want to use). Subtract this # from the loaded arch in the spreadsheet. That is how much lift you will get (if you end up with a negative # your truck will be lowered by that ammount).

    Does that help?
    Clear as mud?
     
  15. zcarczar

    zcarczar 1/2 ton status

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    Im resurecting this one from the dead, but Dan the link is dead and I want to use the calculator.
     

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