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SUMMARY: Microstructure matters: why smaller is often (but not always) str
 onger
DTSTART:20130930T131500
DTSTAMP:20260508T120348Z
UID:0eafb5697c7a77cad3196356579bb5d8cb19810d941957da412518d1
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Erica Lilleodden\, Helmholtz-Zentrum Geesthacht\, Germany\
 nBio: Erica Lilleodden is a Materials Scientist at Helmholtz-Zentrum Geest
 hacht in Germany. Her research efforts are focused on mechanisms of deform
 ation and fracture in structural materials\, with particular interest in t
 he effects of microstructural and geometric length-scales. She received he
 r Ph.D in 2002 from Stanford University\, working with W.D. Nix on size ef
 fects in plasticity of metallic thin films.  She then spent nearly 3 year
 s at Lawrence Berkeley Laboratory and University of California Berkeley as
  a Post Doctoral Fellow and Lecturer\, where she used micro-Laue diffracti
 on and in situ TEM techniques to study heterogeneities in plastic deformat
 ion.   She moved to Germany in 2004 as a Humboldt Fellow at the Forschun
 gszentrum Karslruhe investigating the deformation of nanoporous gold and d
 eveloping small-scale mechanical testing methods. In 2006 she moved to the
  Institute of Materials Research at GKSS (now called Helmholtz-Zentrum Gee
 sthacht)\, where she is Head of the Department of Experimental Materials M
 echanics (since February 2010).\nSize effects in plasticity have received 
 much attention in recent years\, due to increased resolution in experiment
 al capabilities\, and the development of materials at small geometric and 
 microstructural length scales. In particular\, the hardness of many materi
 als have been shown to decrease with increasing depth of indentation\, the
  so-called indentation size effect (ISE). In order to circumvent the coupl
 ed effects of extrinsic strain gradients\, as are encountered in nanoinden
 tation\, microcompression testing has become a widely used method to under
 stand the effect of geometric length scale on deformation behavior. In the
 se experiments\, a columnar structure is fabricated\, typically using Focu
 sed Ion Beam (FIB) machining from a thin film or bulk specimen\, with diam
 eters on the order of tens of microns down to 100 nanometers. The columns 
 are then compressed using a nanoindenter outfitted with a flat punch inden
 ter. As in the indentation experiments\, results for many materials show a
  general trend of increasing strength with decreasing deformation volume. 
 However\, the result is not ubiquitous. It is demonstrated here that the c
 ritical parameter which dictates the presence of a size effect is not the 
 sample size or deformation volume alone\, but rather the relative deformat
 ion length-scale relative to the representative microstructural length-sca
 le. This observation holds for both microcompression and conventional nano
 indentation experiments\, and can be used to model size effects in terms o
 f classical laws. The talk will focus on single crystalline\, high purity 
 Mg and the Mg alloy AZ31 of two orientations associated with dislocation p
 lasticity (i.e.\, no twinning)\, where the active slip systems for the two
  orientations have significantly different Peierls barriers. In this way\,
  the influence of intrinsic lattice strength and alloying content can be d
 ifferentiated. Additional results from other “microstructurally rich” 
 materials will also be drawn upon to support a picture of size effects in 
 plasticity as dependent on the interplay between microstructural and geome
 tric length-scales.
LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201
STATUS:CONFIRMED
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