Abstracts - Conference Planning and Management - Iowa State ...

Determination of Nano-scale Mehanical Properties near Hybrid Fiber Interfaces in
Polymer Systems
Charles Wood
Northwestern University
2145 Sheridan Rd, Mechanical Engineering, Evanston, 60208, US
Phone: 352-262-2841, Email: cwood@u.northwestern.edu
L. Catherine Brinson
Northwestern University, Evanston, IL
Abstract:
Hybrid composites involve a designed incorporation of nanoparticles into a traditional composite to
improve matrix properties in areas prone to failure, e.g. interlaminar areas. Hybrid fibers, where carbon
nanotubes are incorporated directly attached to traditional aligned fibers, provides a unique approach to
strengthen specific areas of weakness by controlling the placement of nanoparticles in the matrix.
Incorporation of designed nanoparticle phases in hybrid composites demands understanding polymer
property changes near interfaces, due to the enormous surface area of nanoparticles exposed to polymer
in the matrix. Near attractive interfaces, mobility of the polymer chains is restricted due to geometric
and chemical interactions. The regime of altered polymer properties, the ‘interphase’, extends in a
graded fashion deep into the matrix due to the macromolecular nature of polymers. While previous
studies have shown clear effects on thermomechanical properties of polymers near interfaces in thin
films, direct mechanical investigation of the interphase has been limited. Nanoindentation provides a
unique technique to probe structures at small length scales to obtain properties such as hardness and
elastic modulus associated with surface interactions. In these hybrid composite systems, coupled use of
finite element (FE) models with experimental data is critical to assess the complex structures associated
with the nanotube coated fibers; where surfaces of interest can be located underneath free surfaces
and/or complicated by neighboring surfaces. In this study, nanoindentation techniques are employed to
directly measure interphase properties in an epoxy(Epon 828/NMA)/hybrid fiber system. Two types of
hybrid fibers were studied, carbon and glass parent fibers, with carbon nanotubes (CNTs) grown
radially on the surface of the parent fiber. Nanoindentation was employed to probe discrete areas to
quantify interphase gradients due to the incorporation of CNT growth. The nanoindentation
experiments are accompanied by numerical analysis and fiber pull-out studies to assess the strength
enhancements, and their resulting dimensions, due to the incorporation of CNTs.
Society of Engineering Science ▪ 47 th Annual Technical Meeting 312