Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Life of a spring

  1. Feb 5, 2007 #1
    hi,

    Our counterparts have designed a spring for a valve application.
    the entire component depends on the tension of the spring
    We need to calculate the tension life of a spring(i.e the duration for which the tension in a spring remains a constant)
    Please provide me a solution

    Thanks
     
  2. jcsd
  3. Feb 5, 2007 #2

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I don't know if there's specific studies on springs, but there are more likely to be creep tests for different materials under different fixed stresses. I would imagine the decay of the spring restoring force to be strongly correlated to the creep-related stress relaxation of the parent material.
     
  4. Feb 5, 2007 #3

    Astronuc

    User Avatar

    Staff: Mentor

    Normally a spring would be used well within its 'elastic range', i.e. such that the peak local stress was well below is yield strength. Creep would only be an issue if it was in a heated environment with the operating temperature above about 0.35 of melting temp.

    Fatigue may be the limiting case, and that depends on the fracture toughness and fatigue resistance of the material, as well as the largest allowable imperfection in the material.

    See if you can find a Langer-O'Donnell curve (fatigue cycles to failure for a given stress level). Sometimes is called O'Donnell and Langer model (or curve). However, those are names in the nuclear industry.

    Alternatively, look for S-N curve, or search google for "S-N","fatigue", e.g.
    http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/S-NFatigue.htm
     
  5. Feb 5, 2007 #4

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Oops. I misuderstood the OP (particularly the bit in parentheses) to mean the spring was under constant tension during its entire life (i.e., no cycling loads).
     
  6. Feb 5, 2007 #5

    Astronuc

    User Avatar

    Staff: Mentor

    Well it's not really clear. The actual operation needs to be discussed in more detail. Depending on the valve, it might be under constant tension with very infrequent change. If it is a control valve, then there is a good chance that there is some type of variation in load - even if it's high frequency, low amplitude. I believe Richard Hertzberg (Lehigh Univ) has looked at this phenomenon.

    Deformation and Fracture Mechanics of Engineering Materials

    I met him when during a presentation to our local ASM chapter. Nice guy.

    http://www.lehigh.edu/~inmatsci/faculty/hertzberg/Hertzberg.htm
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Life of a spring
  1. Creep and Fatigue Life (Replies: 3)

Loading...