Theory of workhardening 1934-1984
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EARLY THEORIES
A. The Introduction of the Dislocation Concept into Materials Science W H E N , in 1934, Orowan, 1-5 Polanyi, 6 and Taylor7 almost simultaneously introduced the dislocation concept into solid state theory, they immediately applied it to the plastic properties of metals. Specifically, G. I. Taylor7 derived a "static" theory of workhardening on the basis of dislocation stress interactions, and E. Orowan 1-5 contributed a characteristically wide range of ideas pertaining to the "dynamic" concept of crystal plasticity. In fact, Orowan developed a rather comprehensive system of geometrical considerations and equations built on Richard Becker's basic thought8'9 that the plastic properties of crystalline materials could be understood through a strongly stress-dependent flow rate. This suggestion had found support through some preliminary measurements by Becker and Boas 8'1~but was at variance with the prevailing "static" concept according to which in crystalline materials there exists a direct correlation between stress and strain, in contrast to amorphous materials exhibiting viscous flow, i.e., a direct correlation between stress and flow rate, but not between stress and strain. Orowan's 1934/5 series of papers 1-5 was triggered by his insight that the previously unexplained elementary glide processes appearing in Becker's theory could be variously DORIS KUHLMANN-WILSDORF is University Professor of Applied Science, University of Virginia, Charlottesville, VA 22901. This paper is based on a presentation made at the symposium "50th Anniversary of the Introduction of Dislocations" held at the fall meeting of the TMS-AIME in Detroit, Michigan in October 1984 under the TMSAIME Mechanical Metallurgy and Physical Metallurgy Committees. METALLURGICAL TRANSACTIONS A
identified with the generation of dislocations and also with increments in their motion. Orowan did not invent the dislocation concept, however, but gave full credit to Polanyi, citing Reference 6 and saying that the "effect of 'dislocations' to enhance plasticity has been recognized by Polanyi already for years." In turn, Polanyi6 acknowledged his indebtedness to earlier concepts which prefigured dislocations, including those due to Prandtl,l~ Dehlinger, 12and his own with Masing.13 None of these, but only G.I. Taylor, realized that in mathematics dislocations already had a long history, and that the geometry and stresses of dislocations of various types had already been extensively treated by mathematicians. In his workhardening theory7 he employed the solutions for the stresses of straight edge dislocations, which he found in Love's book. 14 Thus Taylor incidentally also introduced the word "dislocations", whereas the German word "Versetzungen" appears to have been coined by M. Polanyi. Alas, only very few scientists continued to be interested in creep and workhardening and almost no additions were made to dislocation theory as such for a number of years, even while the dislocation concept was used in discussions of metal plasticity. Prominent con
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