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7.13: Questions

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    Quick questions

    You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

    1. What is the ratio of the minimum shear stress required to operate a Frank-Read source for work-hardened copper (ρ = 1014 m-2) and annealed copper (ρ = 1010 m-2)?
      a 1
      b 10
      c 100
      d 1000
    Answer

    C

    Which of the following about cross-slip is true?

    a Cross-slip is favored by a high stacking-fault energy
    b Cross-slip is favored by a low stacking-fault energy
    c Edge dislocation can bypass obstacles via cross-slip
    d None of the above
    Answer

    A

    Which type of intersection is most important to work hardening?

    a edge-screw intersection
    b edge-edge intersection
    c screw-screw intersection
    d none of the above
    Answer

    C

    Which of the following is not a pinning site in forest hardening?

    a Lomer lock
    b jogs
    c kinks
    d precipitates
    Answer

    C

    Which of the following about poly-crystals is/are true?

    a Poly-crystals do not exhibit any easy glide
    b Poly-crystals tend to have higher yield stresses than single-crystals
    c Poly-crystals with smaller grain sizes have higher yield stresses
    d All of the above
    Answer

    D

    Deeper questions

    The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

    1. Explain why the intersection of two screw dislocations is important to work hardening.
    Answer

    The intersection of two screw dislocations produces jogs of edge orientation in both screw dislocations which can only move by climb. Because dislocation climb is a thermally activated process, the movement of the jogged screw dislocation will be temperature-dependent. At temperatures where climb cannot occur, the motion of screw dislocations will be impeded by jogs (i.e. the jogs are sessile) and so the crystal becomes work hardened.

    This page titled 7.13: Questions was last modified on Thu, 26 Nov 2020 20:29:34 GMT and is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Dissemination of IT for the Promotion of Materials Science (DoITPoMS) via source content that was edited to the style and standards of the LibreTexts platform.

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