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Plasticity of Rock Salt and the Taylor and Becker-Orowan Theories of Crystalline Plasticity



IN Prof. Taylor's theory of crystalline plasticity1 the process of slip is conceived as the result of the propagation through the lattice of a definite type of deviations from the ideal structure, so-called dislocations2. The path of a single dislocation in general is limited by the faults or flaws in the crystal and it is assumed that the number N of propagated dislocations increases during the course of the process. Every dislocation is the centre of a field of stress; the various dislocations influence each other's motions and it is shown that centres will escape from each other only if the applied exterior stress exceeds a certain value, increasing with N. Hence the stress necessary for further deformation increases with the deformation already attained (shear hardening). It is suggested by Taylor that the dislocations might arise as a consequence of thermal agitation, but no explicit explanation is given of the progressive increase of N.

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  1. 1

    G. I. Taylor, Proc. Roy. Soc., A, 145, 362, 388, 405; 1934.

  2. 2

    Compare also M. Polanyi, Z. Physik, 89, 660; 1934.

  3. 3

    R. Becker, Physik. Z., 26, 919; 1925. E. Orowan, Z. Physik, 89, 605, 614, 634; 1934.

  4. 4

    This will be set forth in more detail in Chapter V (section 11) of a “Report on Viscosity and Plasticity” published by the Royal Academy of Sciences at Amsterdam in its Verhandelingen (section I, 15, No. 3; 1935).

  5. 5

    A. Smekal, Z. Physik, 93, 166; 1935.

  6. 6

    W. Ewald and M. Polanyi, Z. Physik, 28, 29; 1924. M. Polanyi, ibid., 89, 660; 1934.

  7. 7

    See, for example, K. Wendenburg, ibid., 88, 727; 1934.

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