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4
2 Metals – Use and
Properties
The properties of metallic materials –
metals and metal alloys – cover a
very broad spectrum. The distinction
between function and structure also
applies to materials; examples of
structural and construction materials
include materials for machine and
plant building, precision engineering
and civil engineering, while functional
materials are used in areas such as
electrical engineering, electronics
and media technology.
With construction materials the
emphasis is on mechanical properties
such as strength, rigidity
(elasticity) and ductility (plasticity) at
working temperature. These
characteristics are the main influence
in testing-machine design
(maximum required test load for load
frames and load cells) and equipment
(high-resolution extensometers
for Young’s Modulus determination).
As an illustration, steel under
mechanical loading displays very
high stiffness right from the beginning
of the test – unlike rubber, for
example. This results in large load
increases for very small deformations,
often less than a hairsbreadth.
These deformations are elastic and
decrease again with load reduction.
Only when the load is further
increased is a plastic (i.e. permanent)
deformation superimposed on
the elastic deformation.
Specimens of very brittle materials
(such as cast iron) or soft steels at
low temperatures fracture without
warning on reaching cohesive
strength (i.e. with no prior necking).
Fig. 1: Load-extension curve of sheet-steel tensile specimen (upper) and enlarged view of
the area until just after 0.2 % proof stress (lower)
By contrast, local stiffness in tough
materials decreases sharply after the
elastic limit has been exceeded and
can even reach values of zero or
less (increase in deformation without
load increase or even with load
reduction).
The load-extension curve of a steelsheet
tensile specimen (gage length
L0 = 80 mm) illustrates very well the
change in stiffness as deformation
increases.
Table: Comparison of Specific Material Properties
Material properties Metals Concrete Plastic mat.
(without extreme values) (non-reinforc.)
• Tensile and compression
strength [MPa] 100 ... 2000 200 ... 500 20 ... 160
• Young’s Modulus [GPa] 70 ... 210 15 ... 40 0,06 ... 6
• Density (specific weigth) [g/cm³] 2,7 ... 7,8 2,1 ... 2,4 1 ... 2
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