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Homework Help: How do I calculate the length of a rod?

  1. May 26, 2012 #1
    1. The problem statement, all variables and given/known data

    I need to calculate the breaking point of a Steel rod.

    2. Relevant equations

    I know the density: 8.03
    Cross section: 1m^2
    Tensile Strength: 500*10^6
    Volume: 62266500.6
    The whole length is: 406700

    3. The attempt at a solution
    Please provide me with explanations and equations which i could use. Thank You.
  2. jcsd
  3. May 26, 2012 #2
    You must attempt a solution before we will help. Furthermore, your problem is vague. How is the rod situated?
  4. May 26, 2012 #3
    I don't have an attempt at a solution because i don't really know what to do at all. There is no information given except for what i wrote above, that's why i have a big problem with solving this..
  5. May 28, 2012 #4
    Material Science right?

    You seem to be asking two questions the length of the rod and the breaking point of the steel correct?

    If you are wondering about the breaking point of the steel it is a trick question the tensile strength is the maximum stress that may be sustained by a structure in tension (it is the top point in the stress/strain curve). If this stress is applied and maintained fracture will result.

    so the tensile strength is the breaking point of steel.

    As for the length of the rod, you have the whole length written up there as 406700. Units would help with all your data.

    I have a few formulas that would work for this problem but with your given information it looks like a 100% trick problem.

    It would be placed in a tensile testing machine, (most if not all of the time vertical) with two crossheads to attach the specimen.
    Last edited: May 28, 2012
  6. May 29, 2012 #5
    I have attached a pic i found of stress strain curve of mild steel,
    Here, the breaking point's stress is given less that maximum stress ...

    EDIT: Forgot to add pic ...

    http://pages.uoregon.edu/struct/courseware/461/461_lectures/461_lecture24/461_lecture24_pic1.gif [Broken]
    Last edited by a moderator: May 6, 2017
  7. May 29, 2012 #6
    If you were to give me that value of stress and I were to look at the chart I would still be at the left side of the curve. How did you get to the right side of the curve?

    The tensile strength is the breaking point, unless the problem has a chart along with it with time through the experiment with the corresponding stress on the specimen. This is the answer they are looking for.

    As an engineer if your design reaches the tensile strength is a broken plastic deformed mess.

    You understand that the slope reaches a max (tensile strength) and then begins to slope down, because the steel has already fractured. Metals are a ductile material though they do not crack into two like a brittle ceramic dinning room plate would. It bends first and the fracture grows, until the fracture is complete and it is in two pieces.
    Last edited: May 29, 2012
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