How to calculate energy density of mainspring?

  1. Jan 24, 2013 #1

    How do I calculate the energy density of either a main-spring (like in a clock) or a motor-spring?
    Can someone show me values put into the correct formula for something like steel?

    I did find some material properties like this:

    The motor-spring I am interested in is a type like this:

    Secondly, I would like to experiment with various materials (composites especially). If I make a plank of this material, how can I measure its properties to be able to put it into the correct formula for energy density of such a spring (if made into a spring)? I would have to take into account the breaking-point of the material of course (i.e. I bend the plank and at some point it either snaps or buckles).

    I did study mech. engineering for a coupple of years but it is 20 years ago and I am rusty ;-)
    I have googled and read a lot but am still stuck. Most stuff only relates to compression-springs but I need to work out spring constant of basically a beam (?) and not sure of to work out the breaking point (of the clockspring) when I know that a certain material will snap when it is deflected a certain amount.

    Thanks a lot.

  2. jcsd
  3. Jan 24, 2013 #2
    A concrete example I would very much like to see is something like this:

    Take an acrylic ruler. it is 30 cm long, 3 cm wide and 2mm thick. It weighs 20grams (just estimated for this example).
    Acrylic has Youngs Modulus of 3.2 GPa and ultimate Tensile Strength of 70 Mpa (according to the page I posted ealier).

    If I took this material and used 500cm of it and turned it into a mainspring (or motor-spring), then:

    a) What is the energy density of the spring?

    b) If I didn't have Youngs Modulus and Ultimate Tensile Strength, how could I work these out (and any other values that I might need)?

    Thanks and regards
  4. Jan 31, 2013 #3

    Sorry I have cross-posted this in the coursework forum, many reads but no answers :-(
    Is no one able to help me with this?
    When I google, I only find articles related to compression springs. Why is it so difficult to find stuff on main-springs?

    Can someone recommend a good book on the subject? Not interrested at all in compression-springs, only main-springs and tensator springs and the like.

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