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Math Help - Strain Gauge Mechanics

  1. #1
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    Oct 2008
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    Strain Gauge Mechanics

    I have some strain gauge calculations to complete to produce a mohr-coloumn circle for rock mechanics, but I seem to be missing a trick with completing the initial calculations.

    To be honest, the application probably doesn't matter as the bit I'm stuck on is more a rearrangement of equations.

    Q is the radius of the circle which is what I am trying to find, along with E1 and E2 to produce the circle.

    The example I have runs through as follows:

    Q.Cos 2θ = -363
    Q.Sin 2θ = -90.64
    Q2 = Q2.Sin2 2θ+ Q2Cos2 2θ = 131769+8215.61
    Q = 374.15


    The 2's in green are to represent squared symbols as I can't produce an elevated 2 in the message composition box.

    I have calculated Q.Cos 2θ and Q.Sin 2θ for my problem, but can't figure out how to get Q2.Sin2 2θ+ Q2Cos2 2θ as eveything is squared apart from 2θ. Am I missing something obvious?!

    All help would be greatly appreciated.
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  2. #2
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    Joined
    Oct 2008
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    I found a way of solving the above using the following, but I still don't get how the example sorts things through.

    tan2θ = 0.249
    2θ = tan-1 0.249 = 13.98
    θ = 7

    Q.cos13.98 = -363
    Q.0.970 = -363
    Q= -374.2
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