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Eighty Years of Dislocation Theory and Work Hardening

Kamyar M Davoudi's picture

On February 7, 1934, two consecutive papers by Sir Geoffrey Ingram Taylor were received and so the dislocation theory was born and the first attempt at describing work hardening was made. Before that date, it was known that there was a big gap between the ideal and the experimentally observed shear strength. While according to the calculations, the shear strength had to be of the order of one tenth (or with finer models one thirtieth) of the shear modulus, the measured shear strength was several orders of magnitude smaller. This large discrepancy brought about Geoffrey I.Taylor, Egon Orowan and Michael Polyani to independently postulate the existence of dislocations. Papers by Orowan and Polyani were published consecutively in one volume of Zeitschrift für Physik.

The mathematical concept of dislocations, however, had been originally developed by Vito Volterra three decades before, in 1907. 


Since 1934, great achievements have been gained in the field.. Two decades later, in the 1950s, dislocations were directly observed for the first time with the help of electron microscopes. John D. Eshelby, Nevill F. Mott (Nobel laureate), Frank R. N. Nabarro, Sir F. Charles Frank, Thornton Read, Jacques Friedel, Sir Alan H. Cottrell, William Shockley (Nobel laureate), John P. Hirth, Jens Lothe, Johannes and Julia R. Weertman, Toshio Mura, and Kocks were among those who made important contributions to dislocation theory and work hardening models. Several books have also been written on this subject. Since  1979 until today, , sixteen volumes of the series Dislocations in Solids have been devoted to all aspects of the dislocation theory. 

Experiments, and now simulation techniques have helped us develop an ever growing knowledge of dislocations. . While most individual processes,  have been well studied,  the collective motion of dislocation is still being investigated. Plastic deformation, work hardening of crystalline materials and even size effect, which has attracted much attention these days, are mainly attributed to the collective motion of dislocations.

In 1953, Alan Cottrell in one of his books stated "[work hardening] was the first problem to be attempted by dislocation theory and may be the last to be solved." In 2002, volume 11 of Dislocations in Solids, Cottrell, on a brief view of work hardening wrote, "it is sometimes said that the turbulent flow of fluids is the most difficult remaining problem in classical physics. Not so. Work hardening is worse." Despite all the effort devoted to this area, as Ladislas P. Kubin recently mentioned there is currently no generally accepted theory explaining all aspects of it. With new techniques being developed everyday, our knowledge on the subject is certain to continue growing through the years.

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