Effective Behavior, Microstructure Evolution,
and Macroscopic Stability
in Polymeric Composites
Mr. Oscar Lopez-Pamies, Ph.D. Candidate
Advisor: Professor Pedro Ponte Castañeda
Department of Mechanical Engineering and Applied Mechanics
University of Pennsylvania
Abstract
Polymeric composites are currently used in numerous commercial
and military applications, and have shown great promise
for utilization in new technologies. There is then a practical,
as well as theoretical, need to understand the connection
between the underlying microstructure of polymeric composites
and their mechanical and physical properties, and how the
latter may be enhanced with changes in the former. In this
connection, we have developed an analytical, nonlinear homogenization
framework for determining the overall response of polymeric
composites subjected to finite deformations that not only
captures the macroscopic response of these composites, but
is powerful enough as to predict their failure. The framework
accounts for the evolution of the underlying microstructure,
which results from the finite changes in geometry induced
by the applied loading. This point is key as the evolution
of the microstructure can have a significant geometric softening
(or hardening) effect on the overall response of the material,
which, in turn, may lead to the possible development of
macroscopic instabilities. The main concept behind these
nonlinear homogenization methods is the construction of
suitable variational principles utilizing the idea of a
“linear comparison composite,” which allows
one to convert available linear homogenization estimates
into analytical estimates for the large-deformation overall
response of the nonlinear polymeric composites. Following
the presentation of the general theory, we show applications
for reinforced and porous rubbers, as well as for thermoplastic
elastomers. The connection between the evolution of the
relevant microstructural variables (i.e., porosity, particle
rotation) and the macroscopic failure in these materials
will be put into evidence for all three cases.
Tuesday, April 11th
303 Towne Bldg.
12:00 – 1:00 p.m.
