Sakae Takeuchi1, Hidezi Suzuki1
The two assumptions under which a thermodynamical theory of plastic deformation has been develoted by us in the preceding report, were discussed from a view point of the dislocation model.
i) Slip in a crystal occurs through a movement of dislocation in the slip plane, in which the potential field can be represented approximately by a sinus function with a period of one at mic distance in the simple cubic lattice only, but additionally a field with a period of a quarter of one atomic distance must be added to it in the face centred lattice.
Provided that the dislocation passes through positions of the minimum potential in such a field whea it moves, lattice in the neighbourhood of dislocation centre must transform to the different type of lattice at every. quarter of one atomic distance four times, while the dislocation moves one atmic distance, in the following way; face centred lattice→body centred→face centred→body centred→face centred. In the narrow region arround the dislocation centre such a transformed lattice corresponds to a heavily deformed state which is far over the elastic limit.
ii) From the above consideration a mechanical energy E=f.l dissipated for gliding one atomic distance l is equal to the free energy 4 ΔG for the fourhold transformations. Consequently the following, equation is satisfactory
which is the firit assumption in the previous report.
iii) The second assumption in the previous report, crystals having no actual transformation raise the lattice transformation under so high a stress that its magnitude is greater than the critical shear stress, can be immediately satisfied in the restricted region arround the dislocation centre from the above model.
iv) The line dislocation in our modified model is not always perpendicular to its moving direction, but it is at the angle of 60° in the slip plane of face centred lattiec.
v) W hen such dislocation moves, there exists the posibility that vacant holes at the lattice points are left behind it. Existence of these holes gives a resistance against movement of a following dislocation, and results in hardening the crystal.
(Received 1948/09/25 Published 1949/04/20)
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