Biomedical Engineering Reference
In-Depth Information
Table 2.2
Examples of materials that are brittle, of average brittleness, resistant, or ductile
Average
brittleness
Type of material Brittle
Rupture resistant Ductile
Mineral
∇
,
⊕
Graphite,
diamond, glass,
quartz, topaz
Calcite, fluorine
gypsum, mica,
apatite, feldspar
Ta l c
Metal
Gray iron, crude
steel
Bronze, carbon
steel
Iron, nickel,
cobalt, titanium,
tantalum,
martensitic steel
Lead, gold,
aluminum, silver,
copper, tin
Semiconductor
∇
GaAs, InP
Silicon
Ceramic
∇
Alumina, MgO
Carbide, boride,
silicide
,
⊕
Polymer
∇
Thermohardening
polymer
Reinforced
polymer matrix
carbon Fiber
composite
Thermoplastic
polymer
,
Biological
material
∇
Bone, tooth,
spicule
Fingernail,
cartilage, wood
Soft organic
matter
,
⊕
,
Mixed-
composite
materials
∇
,
⊕
,
Concrete
Metal matrix
composite,
ceramic, carbon
and carbon-
fiber, metal and
ceramic
Polymer-metal
: metallic bond;
∇
⊕
: covalent bond;
: ionic bond;
: van der Waals bonds
Mixed-composite materials have different mechanical properties than their com-
ponents. For example, composite materials made from carbon or ceramic fibers
and either resin, metallic, or ceramic matrices have increasingly higher mechanical
properties, respectively. This property enables these materials to be used under high-
temperature and high-pressure stresses (e.g., the conditions required for aerospace
materials).
2.3.4 Mechanical Properties of Organic Materials and Glass Transition (
T
g
)
Chain flexibility is a function of temperature. Therefore, the rigidity and tensile
strength of a polymer are also closely linked with temperature. When an amor-
phous polymer is cooled to below a certain temperature, it becomes hard and
brittle like glass. This temperature (which differs for each polymer) is called the
glass transition temperature and is abbreviated as
T
g
. This thermal transition is
a material-specific physical characteristic. Hard plastics such as polystyrene and
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