Timothy A. Philpot - Mechanics of materials _ an integrated learning system-John Wiley (2017)

CHAPTER3
Mechanical Properties
of Materials
3.1 The Tension Test
To design a structural or mechanical component properly, the engineer must understand the
characteristics of the component and work within the limitations of the material used in it.
Materials such as steel, aluminum, plastic, and wood each respond uniquely to applied
loads and stresses. To determine the strength and characteristics of materials such as these
requires laboratory testing. One of the simplest and most effective laboratory tests for obtaining
engineering design information about a material is called the tension test.
The tension test is very simple. A specimen of the material, usually a round rod or a
flat bar, is pulled with a controlled tension force. As the force is increased, the elongation
of the specimen is measured and recorded. The relationship between the applied load and
the resulting deformation can be observed from a plot of the data. This load–deformation
plot has limited direct usefulness, however, because it applies only to the specific specimen
(meaning the specific diameter or cross-sectional dimensions) used in the test procedure.
A more useful diagram than the load–deformation plot is a plot showing the relationship
between stress and strain, called the stress–strain diagram. The stress–strain diagram
is more useful because it applies to the material in general rather than to the particular
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