Lab 3:
Plastic Deformation
Mechanics of Deformable Solids
Spring 2011
Tension Test
In this Lab, students will be given opportunity to conduct tension tests of metallic materials
and to analyze the data. Tension test is widely used to provide basic design information on
the strength of materials. In the standardized tension test, a specimen is subjected to a
continuously increasing uniaxial extension while simultaneously measuring the tensile
force applied to the specimen. The ASTM standard (ASTM E804) of “standard test
methods for tension testing of metallic materials” can be downloaded from ANGEL. A
typical relationship between engineering stress and engineering strain obtained from a
tensile test is shown in Figure 1.
Figure 1. Stressstrain curve of a tensile test
The point at which the stressstrain relationship changes from linear to nonlinear is
known as the
yield point
. The stress at the yield point is called
yield strength
of the
material. The usual definition of the yield strength is the
offset yield strength
determined
by the stress corresponding to the intersection of the stressstrain curve and a line parallel
to the elastic part of the curve offset by a specified strain that is 0.2%. As the applied
stress increases beyond the yield point, the material begins to deform plastically and
changes its shape permanently. During the plastic deformation, the crosssectional area of
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 Spring '11
 SoonsungHong
 Deformation, Tensile strength, σ, angel, true plastic strain, εe

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