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SUMMARY:MEchanics GAthering -MEGA- Seminar: Beyond classical thermodynamic
 s: dislocation-mediated plasticity
DTSTART:20190321T161500
DTEND:20190321T173000
DTSTAMP:20260412T113026Z
UID:14398eb5a5e5d7b433704808f395af05a9d0ea13d9b328256ff9a1e8
CATEGORIES:Conferences - Seminars
DESCRIPTION:Victor Berdichevsky\, College of Engineering\, Wayne State Uni
 versity\nAbstract At the dawn of dislocation theory there was a hope that
  plasticity can be understood in terms of dislocation interactions similar
 ly to what is done by statistical mechanics of colliding particles in gas 
 dynamics. There was a fascinating challenge to learn how to deal with inte
 ractions of lines instead of points\, but that seemed to be a pure technic
 al issue. It turned out\, however\, that the major difficulty lies in a di
 fferent place. One of the aims of this talk is to explain what the difficu
 lty is and to make an attempt to treat it. It will be argued that the core
  problem is the drastic difference in geometries of dislocation phase spac
 e and phase space of classical statistical mechanics. Due to that thermody
 namics of plasticity is quite different from classical thermodynamics of s
 olids. Briefly\, the major differences are as follows. First of all\, seve
 ral additional thermodynamic parameters come into play – dislocation po
 larization tensor\, stress resistance tensor\, entropy and temperature of 
 microstructure. In a sense\, polarization is similar to density in gas dyn
 amics while stress resistance bears some properties of pressure. In contra
 st to gases where molecules keep moving when mass density is constant\, in
  crystals the dislocation ensemble becomes frozen as soon as polarization 
 tensor is fixed. Polarization tensor is the collective kinematic character
 istic of dislocation ensembles on which external stresses work. Fixing pol
 arization tensor makes the work zero. In order to deform a crystal\, the a
 pplied stress must exceed the resistance stress. The resistance stress ten
 sor and polarization tensor are linked to entropy and temperature of micro
 structure by some constitutive equations. Entropy and temperature of micro
 structure have simple physical meaning: temperature of microstructure is a
 ssociated with average energy drop in slip avalanches\, while rate of micr
 ostructure entropy is linked to the number of slip avalanches per unit tim
 e. An unusual peculiarity of dislocation-mediated plasticity is the decay 
 of microstructure entropy in monotonic loading.
LOCATION:MED 2 2423 https://plan.epfl.ch/?room=MED22423
STATUS:CONFIRMED
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