Biographical Memoirs Volume 70 (1996) / Chapter Skim
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Egon Orowan
Egon Orowan
Pages 260-319
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References preceded by the letter R refer to numbered papers deposited in the archives of The Royal Society.
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She en c! Egon Orowan met again, en c!
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After initially studying mechanical engineering, then electrical engineering, he transferred to physics uncler the influence of Professor R Becker.
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Griffith shower! that this could be explained by the concentration of the applied Preferences without the prefix R are to publications of Egon Orowan, numbered according to the bibliography at the end of this Memoir.
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eciges hac! tensile strengths up to ten times those usually measurecI, showing conclusively that the usual tensile strength is controller!
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that plastic flow increases the fracture stress when glide planes and fracture planes intersect, but decreases the fracture stress when these planes coincide, as for basal glicle en c! fracture in zinc.
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a reversing rolling mill. Once a week, to soothe nerves en c!
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a trace of plasticity left at the temperature of liquid air: Becker's theory demanclec! complete brittleness at very low temperatures.
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at the important conclusion that the phenomena of crystal plasticity cannot be explained by ther
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It sets out to show that the "static" theory of creep, in which steacly-state creep results from a balance between the rate of work hardening en c! the rate of recovery by softening, must be replaced by a "dynamical" theory baser!
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Six At (3) Here 36/~'c is the rate of work hardening, -36/3t the rate of recovery.
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at low temperatures.) Assuming the rate of work hardening to be constant, Orowan further moclifiec!
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The clisIocation acts as a "stress concentrator" in the sense that the shear stresses it exerts on the glide plane are of opposite sign in front of it en c! behinc!
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Schematic picture of a local gliding; section in the glide direction perpendicular to the glide plane. The lattice was linear and orthogonal before loading; the dislocation zones are circled.
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EGON OROWAN 275 clisiocations were important enough to warrant a publication, en c! I wrote to Polanyi, with whom I cliscussec!
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with showing by quantitative arguments that the "clynamical" theory represents the reality of plastic deformation much better than cloes the "static" theory with the superposition of recovery. It begins with the analogy between the static theory en c!
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to that favourec! by the applied stress.
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the clomain boundaries would act as nuclei of mechanical or electrical breakdown. Orowan pointer!
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en c! a systematic secondary structure (of Tower energy than the perfect crystal)
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alternating stress is too low to cause plastic deformation in the matrix. The stress amplitude in such a region falls below that in the matrix by an amount which is proportional to the plastic strain amplitucle in the soft region.
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that at small stress amplitucles the Bauschinger effect wouic! be important, small reverse strains occur quasi-elastically, without causing work hardening.
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"the constancy of the activation energy means that secondary creep is a flow by strain hardening recovery and thermal softening". This approach, amplified in (27)
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It led to a paper The Calculation of Roll Pressure in Hot and Cold Flat Rolling (27) which occupied 28 large pages of small print, and led to ten pages of printer!
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there is no plastic deformation. The investigation involves!
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formulae for roll pressure en c! power consumption for hot rolling where the flow stress is low (anc!
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observed that, if the cleavage strength of the steel was less than about three times the yield stress, then notch brittleness was only to be expected. The mariners noted that the casualties were mostly in the North Atlantic, and therefore the ships should take care to take more southerly courses in warmer waters.
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The ideas that Orowan developed while working on the notch brittleness contract were mostly included in the review article (39) on fracture that he wrote for Reports on Progress in Physics several years later.
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Orowan was especially clever at bringing to bear on problems very simple ideas of stress analysis. For example, in the work on notch brittleness he appreciated the connection between the stress enhancement in a tensile specimen containing a deep notch and the problem of indentation by a circular punch; it was a matter of changing the sign of the stresses in the punch problem and so turning compression into tension.
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He brought into glaciology for the first time the notion that creep, as studied in metals by Andrade many years before, was the basic mechanism of glacier flow. He then, characteristically, suggested the approximation of perfect plasticity with a constant yield stress and introduced three very simple models.
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Vaughan Lewis later persuaded Orowan to join him in a tour of Swiss glaciers with Professor Hollingworth, the geologist of University College, London (on a grant from the Royal Society)
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have no practical importance for applications in engineering." On notch brittleness, to which he en c! his collaborators macle such important contributions, he says "it is a much cliscussec!
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why there is a size effect in notch brittleness on the scale of centimetres. A square roe!
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Steel Research Association in which a single Luclers bane! was causer!
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With All Argon, we had lunch in Walker, where we met to try to help Egon with his arrangements to go to London to celebrate the events of 1934 at a meeting of the British Institute of Metals and the Royal Society, where he was to appear on a platform with Mott and Cottrell and others. It seemed to me that Egon wasn't very keen to go, but he did allow himself to be persuaded by All and myself in a fairly short space of time, and I had the impression that he allowed himself to be persuaded simply because he wanted to talk to both of us about the Cottrell explanation of the strain aging of steel which he considered to be wrong.
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The seconc! paper considers the interaction between internal stresses and the stress required to unlock a clisiocation from an atmosphere, en c!
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The MIT archives contain a letter from E.P. Wigner inviting him to Princeton, one from F
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with a view to a permanent appointment. Chadwick wrote to Orowan cluring this trial period, outlining what hac!
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traditionally a strong materials division, Orowan brought a fresh new mechanistic point of view to the teaching and research of mechanical behavior of materials. During the period beginning in 1950 and extending to his formal retirement in 196S, Orowan continued to oc
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out was greatly appreciated. While always cordial in his interactions with his research students or collaborators, Orowan maintainer!
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was the brittle fracture of ship steel. With his first cloctoral student Davic!
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, stimulates! by his inclustrial consulting arrangement with the Pittsburgh Plate Glass Company, in connection with their new float-glass process for the procluction of plate glass.
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, creep by cliffusional flow and by grain boundary sliding, and finally, mechanistic reasons for the non-existence of a mechanical equation of state for plastic deformation. A small section discussing the possible mechanism of plasticity in both simple atomic en c!
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He then cliscussecI, again in very simple terms, by resorting only to orcler-of-magnitucle estimates, important phenomena such as the lattice resistance to clisIocation motion, precipitation strengthening, work hardening, the yield phenomenon in low carbon steel, en c! the nucleation controller!
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solution alloys such as alpha brass en c! monel metal to explore the rate mechanism in crystal plasticity.
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to replace simple elastic or Newtonian viscous behavior. In a popular article in Scientific American (64)
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to the Royal Society in 1978 for publication in the Proceedings. The fate of this paper en c!
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so on. Identifying these cycles as surges Orowan fincis many parallels to these in moclern Western societies where however the role of economics becomes of central importance.
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many consulting arrangements with industry. Two of these, with Pittsburgh Plate Glass Company en c!
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, en c! the Vincent Bendix gold medal of the American Society of Engineering Education (1971~.
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David Martin, is Dean of the School of Education at Gallaudet University, D.C. Susan's memories of Egon's private life are very clear....
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'." There was another "very dark spot" in Orowan's "plasticitycareer", which throws an interesting light both on his thinking and on that of the Royal Society. He submitted a paper "Mechanics of continental drift" (and probably a companion paper)
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· · ~ There are many stories illustrating Egon Orowan's approach to life. Sir Alan Cottrell recalls (R20)
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Susan Martin, The American Institute of Physics Niels Bohr Library, Professor Lazlo Bartha, Sir Alan Cottrell FRS, Mr.
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Bemerkung zu den Arbeiten von F Zwicky uber die Struktur der Realkristalle. Zeits.
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Fracture and Notch Brittleness in Ductile Materials, in Brittle Fracture in Mild Steel Plates, British Iron and Steel Research Association Part 5, 69-78.
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The British Iron and Steel Research Association Report No.
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Condition of High Velocity Ductile Fracture.~7.
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