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

Obtaining yield stress knowing only Poisson's ratio and UTS?

  1. Oct 14, 2013 #1
    Greetings all,

    I have been trying to find a method of calculating the yield stress for a material when only given;

    -The loading type (Two bars soldered together in tension)
    -The dimensions of the shaft and solder (ie thickness of solder, length, cross sectional area)
    -The Ultimate Tensile Strength of the solder
    -Poisson's ratio of the solder
    -The yield and ultimate tensile strength (UTS) of the shafts


    The UTS of the solder is much smaller than that of the shafts so I assume that that is where it is failing first. I feel like not enough parameters are provided to produce a solution, due to not being provided the strain hardening index, the stress co-efficient or Young's modulus.

    An assumption I have been thinking of using is that since the solder is very thin (0.07 cm) and is made of Silver, the UTS of the solder can be approximately equal to the yield strength. But that seems too simple for what I have been given to work with.

    Am I missing something? Any advice is appreciated.
  2. jcsd
  3. Oct 15, 2013 #2


    User Avatar
    Science Advisor
    Homework Helper

    JebronLames9: I currently do not think tensile yield strength (Sty) can be obtained from tensile ultimate strength (Stu) and Poisson's ratio (nu). And I would say, Sty of solder is not approximately equal to Stu.

    If you have typical tin-silver-copper solder (lead-free), I guess (?) the solder average properties are approximately Stu = 42 MPa, Sty = 28 MPa, and E = 35 GPa. How does this compare to the Stu value you currently have for your solder?

    Above, I assumed typical soldering. Are you referring to soldering? Or instead brazing? In brazing, the joint is created at a temperature exceeding 450 C.

    Are you sure your joint is subjected to tensile stress, instead of shear stress? In other words, are you sure you have only a butt joint, between the two bar ends, and not a lap joint?
    Last edited: Oct 15, 2013
  4. Oct 15, 2013 #3


    User Avatar
    Science Advisor
    Homework Helper

    What nvn said, plus the fact the 0.7 mm of solder between the two parts seems a very poor joint. The solder layer seems much too thick.

    In a properly soldered joint, you have a thin layer of solder pulled into the joint by capillary action, and it forms an alloy with the materials that are being joined. Often soldered or brazed joints are actually stronger than the materials being joined.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook