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B Units involving metres

  1. Apr 16, 2016 #1
    Hi. Stress is measured on Pascals. It's force divided by area. Area of course is m x m. So when stress is given it's in units of MN / m2 or MN m-2.

    Okay. I'm looking at something called the Hall Petch equation. There a constant in it labelled k.

    In an example, k is given as 0.45 MN m-3/2

    Does this make any sense or is there an error with the description of k?

    I mean, what is m-3/2? Thanks.

    P.S. Possible that there is an error in the text. And that k is MN m1/2. However, if it is, I still don't know what m is as a unit. In other words I know m2 is - square meters.
    Last edited: Apr 16, 2016
  2. jcsd
  3. Apr 16, 2016 #2


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    The Hall-Petch equation asserts a relation of the form [tex]
    (\mathrm{stress}) = \frac{(\mathrm{coefficient})}{(\mathrm{length})^x}[/tex] or [tex]
    (\mathrm{coefficient}) = (\mathrm{stress})(\mathrm{length})^x.[/tex] It follows that in SI units the coefficient is measured in units of [itex]\mathrm{Pa}\,\mathrm{m}^x[/itex] or [itex]\mathrm{N}\,\mathrm{m}^{x-2}[/itex]. [itex]x[/itex] need not be an integer.
  4. Apr 16, 2016 #3


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    In fracture mechanics, the stress intensity factor for different types of flaws is expressed in units of MPa-m1/2.

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