|Components of Composite Materials
• Matrix phase:
bulk materials such as:
fibers and particulates such as:
|• Interface: area
A composite material is basically a combination of two or more
materials, each of which retains it own distinctive properties.
Multiphase metals are composite materials on a micro scale, but
generally the term composite is applied to materials that are
created by mechanically bonding two or more different materials
together. The resulting material has characteristics that are
not characteristic of the components in isolation. The concept
of composite materials is ancient. An example is adding straw
to mud for building stronger mud walls. Most commonly, composite
materials have a bulk phase, which is continuous, called the matrix;
and a dispersed, non-continuous, phase called the reinforcement.
Some other examples of basic composites include concrete (cement
mixed with sand and aggregate), reinforced concrete (steel rebar
in concrete), and fiberglass (glass strands in a resin matrix).
about the mid 1960’s, a new group of composite materials,
called advanced engineered composite materials (aka advanced composites),
began to emerge. Advanced composites utilize a combination of
resins and fibers, customarily carbon/graphite, kevlar, or fiberglass
with an epoxy resin. The fibers provide the high stiffness, while
the surrounding polymer resin matrix holds the structure together.
The fundamental design concept of composites is that the bulk
phase accepts the load over a large surface area, and transfers
it to the reinforcement material, which can carry a greater load.
The significance here lies in that there are numerous matrix materials
and as many fiber types, which can be combined in countless ways
to produce just the desired properties. These materials were first
developed for use in the aerospace industry because for certain
application they have a higher stiffness to weight or strength-to-weight
ratio than metals. This means metal parts can be replaced with
lighter weight parts manufactured from advanced composites. Generally,
carbon-epoxy composites are two thirds the weight of aluminum,
and two and a half times as stiff. Composites are resistant to
fatigue damage and harsh environments, and are repairable.
Composites meeting the criteria of having mechanical bonding
can also be produced on a micro scale. For example, when tungsten
carbide powder is mixed with cobalt powder, and then pressed and
sintered together, the tungsten carbide retains its identity.
The resulting material has a soft cobalt matrix with tough tungsten
carbide particles inside. This material is used to produce carbide
drill bits and is called a metal-matrix composite. A metal matrix
composite is a type of metal that is reinforced with another material
to improve strength, wear or some other characteristics.