Did anybody ever measured a typical string's Young's module ?

Discussion in 'Badminton Stringing Techniques & Tools' started by gy79bc, Mar 26, 2012.

  1. gy79bc

    gy79bc Regular Member

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    I have no electrical pulling machine, but it would be
    possible to measure it by using:

    T = Y*delta

    T is tension, delta is the strain = difference in length after pull/original (zero tension length)

    Y is Young's module, should be constant for a particular string.

    With electrical pulling machine, we can measure it
    by:

    1. Marking the string length say 80 mm, clamp the
    testing string piece 30mm far away from the marking,

    pull other end starts from 18,20,22,24,26,28,30,32,34,36 LB with each tension setting, measure the length between markings.


    We assuming the string maintens elastical across the
    pulling tension, the Y should be 18/delta_0 = 20/delta_1 = 22/delta_i ... Should be equal if perfect elastic string. delta_i = L_i - L_0

    Once we get the Y of particular string, we can mark the string outside frame before pull, then measure the marking change after pull to get the tension. Initial marking should ensure marking is visible and measurable after the pull.
     
  2. kwun

    kwun Administrator

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    yes, we should do it!

    it will take a fair amount of prep work though.

    first we need to get the right setup.

    the setup should be independent of any external factors, ie, we cannot do it on the racket frame because we don't want any friction from the grommets. we need an rig to do that.

    then we need to isolate any stretching (which is non-linear plastic deformation and Young's modulus doesn't work with that present). to do that we need to completely pre-stretch the piece of string. i'd say do something equivalent of putting constant pull tension on it for at least an hour.

    then we can start measuring.

    the typical electronic machine that we have, the WISE may not be precise enough as it pulls in steps. it is not easy to ask it to do 30lbs and stop there. it jiggles a lot and each time it adds 0.2lbs to it.

    i was thinking doing it by hand. maybe connect a crank to the digital scale and crank it by hand to achieve the constant tension.

    and then we need to do that for many different strings as well. if we get 10 data points for each string, then we can plot stress/strain and then derive Young's Modulus.

    feels like taking Craft and Design classes back in high school again. :)
     
  3. silentheart

    silentheart Regular Member

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    Make sure you use 10 equal length string cut from the same set for each one of the tension. Do you also want to test different model and different manufactures too?
     
  4. gy79bc

    gy79bc Regular Member

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    simple setup

    To Keep things easy and less work. Lets just do this:
    For each (gauge, material composition, surface coating) variation of string,
    we select two or three brands, for each brands we may select a brand new and
    two year old stock.
    If after initial two trials, we found string age is not an issue, then we can
    skip age variation.
    Tension setup: we can use 15LB, 25LB, 35LB just three pull with same test
    string, standard length. Use three pull results to calculate Young value,
    if we concluded after some trials, no need to do 3 pull, then we can just pull
    25 LB.
    If we can get most popular string tested, that would be great. We can mark
    a string before tension it, and observe the how well it holds the tension. In
    turn, we can also verify the manufacturer's claim.
     
  5. Mark A

    Mark A Regular Member

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    The principle is simple, but getting sufficiently accurate readings is a bloody nightmare. We did some Young's modulus for A-Level phyics, and the setup was ridiculously complicated (involving a spirit-level and a vernier scale). However, those with a WISE could cheat it with nothing more than a tape measure.

    Whoever tries this should have the WISE and string clamp as far away from each other as possible. As kwun mentions, the WISE "jiggle" will be a fly in the ointment, but IME the wobbling stops after 15-20 seconds, so readings could be taken there.

    I'm not sure to what the YM will point - repulsion, stiffness, tension holding, or some combination thereof. If BG80 comes out on top, we'll at least know why...
     
  6. kwun

    kwun Administrator

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    will you be able to get me some strings?

    i can get Ashaway and (most likely ;) ) Li-Ning strings but would need help on others ones.

    i have this experiment as well as a different one in mind and it will take some amount of strings. the other experiment deals with string stretch over time.

    i also have CH/SP/JP NBG98 which would be interesting to do a comparative testing as there are claims that CH/SP are inferior. adding US would be interesting too.
     

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