Introduction to Tensile Testing

Topics: Tensile strength, Materials science, Solid mechanics Pages: 29 (6605 words) Published: March 14, 2013

Introduction to Tensile Testing
TENSILE TESTS are performed for several
reasons. The results of tensile tests are used in
selecting materials for engineering applications.
Tensile properties frequently are included in material specifications to ensure quality. Tensile properties often are measured during development of new materials and processes, so that different materials and processes can be compared. Finally, tensile properties often are used to predict the behavior of a material under forms of loading other than uniaxial tension.

The strength of a material often is the primary
concern. The strength of interest may be measured in terms of either the stress necessary to cause appreciable plastic deformation or the
maximum stress that the material can withstand.
These measures of strength are used, with appropriate caution (in the form of safety factors), in engineering design. Also of interest is the material’s ductility, which is a measure of how much it can be deformed before it fractures.

Rarely is ductility incorporated directly in design; rather, it is included in material specifications to ensure quality and toughness. Low ductility in a tensile test often is accompanied by low resistance to fracture under other forms of

loading. Elastic properties also may be of interest, but special techniques must be used to measure these properties during tensile testing, and more accurate measurements can be made by
ultrasonic techniques.

Fig. 1

This chapter provides a brief overview of
some of the more important topics associated
with tensile testing. These include:

Tensile specimens and test machines
Stress-strain curves, including discussions of
elastic versus plastic deformation, yield
points, and ductility
● True stress and strain
● Test methodology and data analysis
It should be noted that subsequent chapters contain more detailed information on these topics. Most notably, the following chapters should be
referred to:

Chapter 2, “Mechanical Behavior of Materials Under Tensile Loads” ● Chapter 3, “Uniaxial Tensile Testing”
● Chapter 4, “Tensile Testing Equipment and
Strain Sensors”

Tensile Specimens and
Testing Machines
Tensile Specimens. Consider the typical tensile specimen shown in Fig. 1. It has enlarged ends or shoulders for gripping. The important
part of the specimen is the gage section. The
cross-sectional area of the gage section is reduced relative to that of the remainder of the specimen so that deformation and failure will be

Typical tensile specimen, showing a reduced gage section and enlarged shoulders. To avoid end effects from the shoulders, the length of the transition region should be at least as great as the diameter, and the total length of the reduced section should be at least four times the diameter.

2 / Tensile Testing, Second Edition

localized in this region. The gage length is the
region over which measurements are made and
is centered within the reduced section. The distances between the ends of the gage section and the shoulders should be great enough so that the
larger ends do not constrain deformation within
the gage section, and the gage length should be
great relative to its diameter. Otherwise, the
stress state will be more complex than simple
tension. Detailed descriptions of standard specimen shapes are given in Chapter 3 and in subsequent chapters on tensile testing of specific materials.
There are various ways of gripping the specimen, some of which are illustrated in Fig. 2. The end may be screwed into a threaded grip, or
it may be pinned; butt ends may be used, or the
grip section may be held between wedges. There
are still other methods (see, for example, Fig. 24
in Chapter 3). The most important concern in
the selection of a gripping method is to ensure
that the specimen can be held at the maximum
load without slippage or failure in the grip section. Bending should be minimized. Testing Machines....
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