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SUMMARY:Reinforced elastomeric materials at large strains - Prof. Pedro Po
 nte Castaneda\, Mechanical Engineering and Applied Mechanics\, University 
 of Pennsylvania\, Philadelphia
DTSTART:20090904T130000Z
DTEND:20090904T140000Z
UID:TALK18368@talks.cam.ac.uk
CONTACT:Ms Helen Gardner
DESCRIPTION:In this talk I will present applications of the "variational l
 inear comparison" nonlinear homogenization technique to generate estimates
  for the effective behavior\, microstructure evolution and loss of ellipti
 city in reinforced elastomers at finite strains. Three special cases will 
 be considered for illustrative purposes: short-fiber composite elastomers\
 , long-fiber reinforced rubbers and thermoplastic elastomers (TPEs). In pa
 rticular\, for the short-fiber composites\, we investigate the rotation of
  the rigid particles in the context of finite elasticity\, and make compar
 isons with Jeffery's solution for rigid particles in a Newtonian fluid. Fo
 r the long-fiber composites\, we make comparisons with Rosen's estimates f
 or the possible development of instabilities (using a two-dimensional lami
 nate model). For the TPEs\, which are block copolymer systems with a hard 
 glassy phase serving to provide reinforcement in a softer rubbery matrix p
 hase\, we explore the effect of structure at two different length scales: 
 a lamellar structure at the nanometer scale and a granular structure at th
 e micrometer scale. In all these material systems\, it is found that even 
 when the constituent phases are strongly elliptic\, their overall behavior
  may lose ellipticity at sufficiently large deformations\, corresponding t
 o the possible development of shear band-type instabilities. The source of
  these "macroscopic" instabilities has been identified with the evolution 
 of the microstructure\, which\, under appropriate loading conditions\, can
  induce "geometric softening" leading to the overall loss of ellipticity.
LOCATION:Oatley Seminar Room\, Department of Engineering
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