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SUMMARY:Microstructure matters: why smaller is often (but not always) stro
 nger - Dr Erica Lilleodden\, GKSS Hamburg
DTSTART:20080229T140000Z
DTEND:20080229T150000Z
UID:TALK10209@talks.cam.ac.uk
CONTACT:Julie Bazin
DESCRIPTION:Size effects in plasticity have received much attention in rec
 ent years\, due to increased resolution in experimental capabilities\, and
  the development of materials at small geometric and microstructural lengt
 h scales. In particular\, the hardness of many materials have been shown t
 o decrease with increasing depth of indentation\, the so-called indentatio
 n size effect (ISE). In order to circumvent the coupled effects of extrins
 ic strain gradients\, as are encountered in nanoindentation\, microcompres
 sion testing is perhaps the most straight forward method to understand the
  effect of geometric length scale on deformation behavior. In these experi
 ments\, a columnar structure is fabricated\, typically using Focused Ion B
 eam (FIB) machining from a thin film or bulk specimen\, with diameters on 
 the order of tens of microns down to 100 nanometers. The columns are then 
 compressed using a nanoindenter outfitted with a flat punch indenter. As i
 n the indentation experiments\, results for many materials show a general 
 trend of increasing strength with decreasing deformation volume. However\,
  the result is not ubiquitous. In this talk\, results from both indentatio
 n and microcompression experiments in microstructurally varied materials (
 e.g.\, single crystalline\, fine-grained\, nano-porous metals) will be pre
 sented. The extent to which a material exhibits a size effect in strength 
 will be discussed in terms of microstructure (in relation to the mean free
  path for dislocation motion) and the effect of finite size on self organi
 zed critical behavior. 
LOCATION:Oatley Seminar Room\, Department of Engineering
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