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Temperature Effects of Young's Modulus for Copper

  1. Dec 10, 2014 #1
    Hello-

    I am running a simulation of a simple brazed copper assembly; brazed at 1050°C. I believe the Young's Modulus will drastically change after brazing at this temperature since the annealed state is "dead soft". My analyst colleague is using an annealed value for E of 15E-6 psi, which isn’t much less than cold-drawn. My deflection values are nowhere near the actual measurements I am empirically seeing, and I’m thinking E must be much less. I have located some graphs that do show E decreasing with temperature, but none close to 1050°C. Qualitatively speaking, I can vigorously swing a length of copper annealed at this temperature and see it bend like a noodle, so the E has to be lower. I am comparing to a behavior of something like lead??

    Since my simulation model really only requires E in terms of the material properties for deflection, I can’t think what else is causing such a discrepancy?? Other boundary conditions are quite simple.

    Anyone have knowledge of material properties for REALLY annealed copper at 1050°C??

    Thank you in advance.

    Chris
     
  2. jcsd
  3. Dec 10, 2014 #2

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    Brazed with what?
     
  4. Dec 10, 2014 #3
    35/65 Au/Cu
     
  5. Dec 10, 2014 #4

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    I can see the Au softening your assembly quite a bit; can't cite numbers or specific sources, just agonies lab technicians had when I was in grad school with assembling apparatus containing Cu and Au for another group. And, actually at NBS.

    "Noodle?" Annealed Cu is not "soft," or ductile, but easily deformed, hence its use in gaskets (one use and they're done).
     
  6. Dec 10, 2014 #5
    Cu melts at 1083°C and we hydrogen braze at 1030°C. So if I run a 1/8-in rod at this tempertaure, a 4-year old could easily bend it, looking like a mini Schwarzenegger. So maybe not a real noodle, but defintely much softer than typical annealed wire or gaskets, which are heated at temperatures much less. Hence, brazed copper is often referred as "dead soft". I would compare the easy of bending to that of lead at the same shape. At this soft, would you agree that E must dcrease??

    Thx
     
  7. Dec 10, 2014 #6

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    We're working at the limits of my knowledge here. The ultimate strengths listed in what references I've got are around 2/3 that of "hard drawn" Cu, though I do not see how one gets a tensile failure without work hardening the stuff; same references include no yield points, leaving Young's modulus as more a guessing game than anything given the state of the art at the time the listed measurements were made. Conceivably more recent, more sensitive equipment has been used at lower stress and strain values, but I'm unaware of such. Functionally, it has to be regarded as something on a par with lead or tin, but subject to rapid work hardening.

    The details on Au-Cu problems have almost all escaped me (other peoples' problems) with the exception of the observation/rediscovery of how easily Au diffuses in Cu in the solid phase at only very moderate temperatures, 200 - 300 C°. Whether that aggravates your problem remains to be seen.
     
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