MATERIALS ENGINEERING CONCEPTS - Materials for Civil and Construction Engineers - page 9

T ABLE 1.1 Typical Modulus and Poisson's Ratio Values (Room Temperature)

10 6 Material Modulus GPa 1 psi : 2 Poisson's Ratio

Aluminum 69-75 (10-11) 0.33

Brick 10-17 (1.5-2.5) 0.23-0.40

Cast iron 75-169 (11-23) 0.17

Concrete 14-40 (2-6) 0.11-0.21

Copper 110 (16) 0.35

Epoxy 3-140 (0.4-20)

Glass 62-70 (9-10) 0.25

Limestone 58 (8.4)

Rubber (soft) 0.001-0.014 (0.00015-0.002) 0.49

Steel 207 (30) 0.27

Tungsten 407 (59) 0.28

Wood 6-15 (0.9-2.2)

stretch, creating an elastic response; then the atoms actually slip relative to
each other. When the load is removed, the atomic slip does not recover; only
the atomic stretch is recovered (Callister 2003).
Several models are used to represent the behavior of materials that exhibit
both elastic and plastic responses. Figure 1.6(b) shows a linear elastic-per-
fectly plastic response in which the material exhibits a linear elastic response
upon loading, followed by a completely plastic response. If such material is
unloaded after it has plasticly deformed, it will rebound in a linear elastic
manner and will follow a straight line parallel to the elastic portion, while
some permanent deformation will remain. If the material is loaded again, it
will have a linear elastic response followed by plastic response at the same
level of stress at which the material was unloaded (Popov 1968).

Strain Strain Strain

Elastic strain
(elastic recovery)

Plastic
strain

(a) (b) (c)

FIGURE 1.6 Stress-strain behavior of plastic materials: (a) example of loading
and unloading, (b) elastic-perfectly plastic, and (c) elastoplastic with strain hardening.