Building Materials, Third Edition

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tips encounter tough matrix materials. An exception to ductile matrix material is ceramic
matrix materials, which are inherently brittle. Composites using ceramic matrices, such as
reinforced concrete, are used in compressive load applications.

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—™  play an important role in determining the properties of composites. An interface
is a surface formed by the common boundary of the reinforced fiber when they are in contact.
It constitutes the bond in between and is mainly responsible for transferring the load from
matrix to the fiber. Shocks, impact, loadings or repeated cyclic stresses can cause the laminate
to separate at the interface between two layers, a condition known as delamination. Individual
fibers can separate from the matrix e.g. fiber pull-out. Consider 1 cm^3 of an unidirectional
composite made from 25
m diameter, continuous fibers embedded in a matrix. If the fibers are
arranged in a square array and are on average 50
m apart, the volume fraction of fibers is
approximately 20%. The total fiber matrix interface area is approximately 314 cm^2 compared to
the 6 cm^2 external surface area. The typical fiber volume fraction in composites is two to three
times the above amount, and the interfacial area increases proportionally. The large interfacial
area significantly affects the properties of composites, in particular the crucial properties of
toughness and ductility.

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1. Fiber reinforced plastics

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Wood (cellulose fibers in a lignin and hemicellulose matrix), Carbon fiber reinforced

plastic or CRP, and Glass-fiber reinforced plastic or GRP (informally, “fiberglass”).

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Short fiber thermoplastics, long fiber thermoplastics or long fiber reinforced thermoplastics,

glass mat thermoplastics, and continuous fiber reinforced thermoplastics.

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2. Reinforced carbon-carbon (carbon fiber in a graphite matrix)


3. Metal matrix composites or MMCs
   White cast iron, Hardmetal (carbon in metal matrix), and Metal-intermetallic laminate.


4. Ceramic matrix composites
   Bone (hydroxyapatite reinforced with collagen fibers), Cermet (ceramic and metal), and
   concrete.


5. Organic matrix/ceramic aggregate composites
   Asphalt concrete, dental composite, syntactic foam, and mother of pearl.


6. Engineered wood
   Plywood, wood plastic composite (recycled wood fiber in polyethylene matrix), and
   Pykrete (sawdust in ice matrix).


7. Plastic-impregnated or laminated paper or textiles
   Arborite, and Formica (plastic).

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Many composites occur naturally for e.g., wood that essentially consists of cellulose fibers in
matrix of lignin, and bones, which are composites of soft protein collagen and hard minerals