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Homework Help: Length of a plate after roll forging?

  1. Nov 16, 2014 #1

    I'm new here. so I hope I posted this question in the right section. For this problem, I have to compute a couple of parameters:

    An Aluminum plate (7075-O) (length 10 [m], thickness 10 [mm], width 40 [cm]) is
    reduced in thickness from 10 to 9,5 [mm]. The radius of the rolls is 25 [cm], number of
    revolutions = 10 [rev/min]
    Calculate with formulas Kalpakjian 6.3, the following parameters:
    a) True strain
    b) Average flow stress
    c) Average flow stress in plain strain
    d) Appearing roll forces
    e) Power needed for this plate thickness reduction
    f) Length of the plate after the rolling process

    I have already computed a, b, d and e. My first question is what do they mean with plain strain (question c)?
    My answer to B is 240MPA, after I found out that the UTS of Aluminium (7075-O) is 228MPA. But what is exactly the difference between question b and c?

    Second question is about f). I might be very simple, but I don't see how to calculate the length of the plate after the rolling process.

    Hope you guys could give me something to start with.

    Thanks in advance
  2. jcsd
  3. Nov 16, 2014 #2


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    Homework Helper

    Are you sure it's not 'plane' strain?
  4. Nov 16, 2014 #3
    I think they mean plane strain indeed, probably a typo
  5. Nov 16, 2014 #4
    Plain strain refers to a 2 dimensional state of strain (as opposed to three dimensional). This is the common way to describe rolling problems, saying that there is no strain in the roll axial direction, so that strain is only along the sheet and perpendicular to the sheet.
  6. Nov 17, 2014 #5
    I'm curious about this question: when the sheet is squeezed by the rolls both the 40 cm and 10 meter sizes would expand by the same percentage right?

    so the final length should be the 10 meters plus the added percentage minus the percentage added to the width right?
  7. Nov 17, 2014 #6
    dragoneyes001, no, the 40 cm dimension hardly changes at all. This is the significance of plane strain; there is no strain (no elongation) in the direction of the roll axis.
  8. Nov 17, 2014 #7
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