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SUMMARY:Why Fracture?– NanoNomology
DTSTART:20131112T131500
DTEND:20131112T141500
DTSTAMP:20260510T235101Z
UID:557c9f20b2523b1ba85edd4a5cf08fbca30b28cbfc5a1841ff631897
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. William Gerberich\, University of Minnesota\, USA\nBio :
  The research careers of Professor Gerberich and his students have spanned
  9 orders of magnitude time (s) and 9 orders of magnitude scale (nm). As a
  graduate student at Berkeley\, he was tagged as someone to help investiga
 te a construction mishap at about the 50th story level of the World Trade 
 Center as it was being built. Who could have known that 40 years later a f
 ormer student of his from the National Institute of Standards and Technolo
 gy (NIST) would be called to investigate the same steel after 9/11.  Stil
 l at Berkeley and shortly afterwards at the University of Minnesota\, he a
 nd his graduate students made the first measurements of the fracture resis
 tance of transformation induced plasticity (TRIP) steels. For thin sheet t
 his produced 1.5 GPa yield strength steels with a fracture toughness of 30
 0 MPa-m1/2\, properties ultimately attracting the interest of Belgian rese
 archers. With less-expensive alloys\, high-end automobile companies incorp
 orated TRIP steel as a side-impact safety feature some 30 years later. In 
 the 70s and 80s\, understanding of high toughness and resistance to hydrog
 en embrittlement culminated with discretized dislocation studies matched t
 o transmission microscopy\n(TEM) observations in the 90s.\nFor studies at 
 the nm scale\, both nanosphere and nanopillar studies of single crystal si
 licon were studied in the early 00s using AFM\, SEM and TEM microscopies. 
 These were among the first in situ experiments showing that theoretical st
 rengths could be achieved in compression even after plastic deformation of
  small sized objects in the vicinity of 100nm.Subsequently for silicon\, 
  it was demonstrated with others that the brittle to ductile transition co
 uld be lowered to room temperature by decreasing size alone.\nTo summarize
  why fracture develops in high strength materials\, and how one might avoi
 d it\, the research is unfinished as a combination of dislocation nucleati
 on\, dislocation shielding and impurity modified thermally-activated proce
 sses clearly hold the keys to future advances.\nAbstract : In any science 
 “nomology” seeks the principles governing phenomena. To apply that to 
 fracture with origins at the scale of interatomic spacings requires a nano
 bot with a portable nanoscope and a picohammer. With no science fiction av
 ailable\, studies at the nm scale of nanosphere and nanopillar single crys
 tal silicon were conducted in the early 00s using AFM\, SEM and TEM micros
 copies.  We were fortunate to produce in situ experiments showing that th
 eoretical strengths could be achieved in compression even after plastic de
 formation of small sized objects in the vicinity of 40-100nm. Subsequently
  for silicon\, it was demonstrated with others that the brittle to ductile
  transition could be lowered to room temperature by decreasing size alone.
  Taking it to the next level really requires such length scales coupled to
  the appropriate temporal and temperature scales to develop sufficient “
 nomology”. What is meant by sufficient are those measures also accessibl
 e to computational materials science for producing mutually validating res
 ults.\nTo summarize why fracture develops in high strength materials and h
 ow one might avoid it:  -- not possible as such research is zeroth order.
   A combination of dislocation nucleation\, dislocation shielding and imp
 urity modified thermally-activated processes holds the keys to future adva
 nces.
LOCATION:GC B3 31 http://plan.epfl.ch/?room=GCB331
STATUS:CONFIRMED
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