8
1 Summary of Elasticity Theory: Basic Concepts
1.7 Elongation of Steel Specimens
Primary mechanical characteristics of most construction materials are defined in
experiments for uniaxial compression of cylindrical or prismatic specimens. The
appearance of such a specimen before (dashed lines) and after (solid lines) the test
is given in Fig. 1.2.
Figure 1.3 shows an exemplary dependency diagram for the resultant value (P )
of forces elongating the specimen of structural steel, and elongation ((l) of the
specimen. This diagram is automatically plotted using the diagrammatic device
during elongation experiments almost in all existing pull test machines.
In such tests, we can see a homogeneous strain of the specimen everywhere at
a sufficient distance from its ends. Figure 1.3 shows, in a dashed line, that part
of the diagram corresponds to the homogeneous strain of the specimen due to the
formation of local narrowing (neck) shown in Fig. 1.2.
Relative longitudinal strain in the direction of the elongating force is the value
ε 1 =
l
l
,
whereas l is the working length of the specimen (Fig. 1.2). Transverse relative
deformation (ε 2 ) is the value of relative elongation in the direction perpendicular
to the specimen axis. Normal stress is the force attributable to the unit of area F of
normal section of a non-strained rod, e. g.
σ 1 =
P
F
.
(1.2)
Fig. 1.2 Specimen for elongation test
Fig. 1.3 Dependency of
specimen elongation on
elongating force