Composite Materials Research Progress

116
W.H. Zhong, R.G. Maguire, S.S. Sangari et al.
results, there is still a critical lack of comprehensive mathematical modeling that is needed to
be used to make effective predictions for processing-structure-property relationship or when
evaluating the multi-functionalities. An example is the wide array of electrical conductivity
percolation threshold values for certain nano-fillers (e.g. CNT or CNF), when combined with
the goal of improved strength and modulus. Modeling can increase the speed of selection and
reduce the scale of actual testing, a huge advantage for bringing new products quickly to
market. Mathematical modeling also provides practical benefits to industry in developing
modeling capabilities for designing new materials. With the added dimensions of the
nanocomposites options, conventional testing and down-selection for choices between the
various and numerous materials can quickly become unfeasible.
Nanostructures have unique physical and chemical properties different from bulk
materials of the same chemical composition. The mechanical, electrical, thermal and
magnetic properties of composites consisting of an insulating matrix and dispersed
nanoparticles have been extensively studied over the past few decades. The significant
progress in the understanding of nanocomposite systems within recent years has shown that
multifunctional nanocomposites offer both great potential and great challenges, marking it as
a highly active field of research. The research is continuing at an increasing pace, as the
requirements for stronger and lighter materials are needed by a variety of industries.
However, much research effort is continuing toward the development of new processing
techniques that control the purity and dispersions of nanoparticles in the polymers.
2. Hybridization
As composites develop and improve, and their applications grow, there will be inevitably, the
realization that there are limitations and compromises in changing from metals to “nonmetals”.
In many cases, the logical thought process is to consider how the best of both
materials can be in included in hybrids. One of the major subsets of this segment of materials
is based on the concept of going with one of the composites most valuable characteristics, that
is, lamination of individual plies. In some cases the concept that comes most readily to mind
is the replacement of one or more composite plies with metal foil or sheet and these are
generally referred to as Fiber Metal laminates or FMLs.
FMLs were first developed at Delft University in the Netherlands in the early 1980s, and
marketed by Aluminum Company of America (Alcoa), combining sheets of aluminum in an
alternating pattern with plies of traditional composite. As a result of this hybridization FMLs
can theoretically combine the best of both the metal and the composite materials. The first
FML was ARALL® (ARamid-ALuminum Laminate), a combination of aluminum and
aramid/epoxy. This fiber-aluminum adhesive-bonded laminate is a super-hybrid composite
material, which has many attractive properties such as good damage tolerance property, very
high fatigue crack growth resistance, and high static strength along the fiber direction. The
characteristics of ARALL® also include low density and resistance to the effects of
temperature, humidity and acidity/alkalinity, etc.
But greater applications became apparent if the aramid fiber composites were replaced by
the ubiquitous glass fibers composites. In the 1980s, Delft developed a glass/epoxy FML
called GLARE (GLAss-REinforced) composed of thin layers of aluminum sheet or foil
interspersed with layers of fiberglass composite prepreg. The pre-preg layers may be aligned