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UID:71e9e97d9ad61a4f3eaaaea61de98722
CATEGORIES:Mathematical Physics Seminar
CREATED:20211021T140112
SUMMARY:Dislocation Theory: The mysterious disconnect between engineering phenomenology and nonequilibrium statistical physics
LOCATION:Zoom
DESCRIPTION:J.S. Langer\nUniversity of California, Santa Barbara\nDislocation Theory: T
 he mysterious disconnect between engineering phenomenology and nonequilibri
 um statistical physics\nIt has been known for about a century that the defo
 rmability of crystalline solids is determined by the motions of extended li
 ne defects known as dislocations. Unfortunately, in the 1950’s, prominent m
 aterials theorists incorrectly asserted that the second law of thermodynami
 cs was not relevant to dislocations. As a result, with no foundation in sta
 tistical mechanics, dislocation theory has consisted primarily of non-predi
 ctive phenomenology, and physicists have mostly lost interest in it.\nIn th
 is talk, I describe a thermodynamic dislocation theory first published in 2
 010. It is based on the second law via an effective-temperature analysis. I
 t also assumes that the controlling time scale is given by the thermally ac
 tivated rate at which entangled dislocations break away from each other. Th
 is theory has been found to agree extremely well with a wide range of exper
 imental observations including strain hardening, grain-size effects, shear 
 banding, and – most recently – fracture toughness. Many fundamentally and t
 echnologically important phenomena remain to be explored from this physics-
 based point of view.\nThe thermodynamic dislocation theory may be illustrat
 ive of a wider range of driven systems in which the internal degrees of fre
 edom fall out of thermal equilibrium with each other but behave in ways tha
 t are consistent with fundamental statistical principles.\n
X-ALT-DESC;FMTTYPE=text/html:<p style="text-align: center;">J.S. Langer</p><p style="text-align: center;
 ">University of California, Santa Barbara</p><p style="text-align: center;"
 >Dislocation Theory: The mysterious disconnect between engineering phenomen
 ology and nonequilibrium statistical physics</p><p style="text-indent: 33.5
 pt;">It has been known for about a century that the deformability of crysta
 lline solids is determined by the motions of extended line defects known as
  dislocations. Unfortunately, in the 1950’s, prominent materials theorists 
 incorrectly asserted that the second law of thermodynamics was not relevant
  to dislocations. As a result, with no foundation in statistical mechanics,
  dislocation theory has consisted primarily of non-predictive phenomenology
 , and physicists have mostly lost interest in it.</p><p style="text-indent:
  33.5pt;">In this talk, I describe a thermodynamic dislocation theory first
  published in 2010. It is based on the second law via an effective-temperat
 ure analysis. It also assumes that the controlling time scale is given by t
 he thermally activated rate at which entangled dislocations break away from
  each other. This theory has been found to agree extremely well with a wide
  range of experimental observations including strain hardening, grain-size 
 effects, shear banding, and – most recently – fracture toughness. Many fund
 amentally and technologically important phenomena remain to be explored fro
 m this physics-based point of view.</p><p style="text-indent: 33.5pt;">The 
 thermodynamic dislocation theory may be illustrative of a wider range of dr
 iven systems in which the internal degrees of freedom fall out of thermal e
 quilibrium with each other but behave in ways that are consistent with fund
 amental statistical principles.</p>
CONTACT:James Langer - University of California, Santa Barbara
DTSTAMP:20260921T114237
DTSTART;TZID=America/New_York:20211117T104500
DTEND;TZID=America/New_York:20211117T114500
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