Agilent Technologies 34901A User Manual page 376

Chapter 8 Tutorial
Measurement Fundamentals
Strain Gage Measurements
Although the instrument does not directly support strain measurements,
you can measure a strain gage using a 4-wire resistance measurement
with scaling. However, BenchLink Data Logger software has built-in
strain gage measurement capability.
When a force is applied to a body, the body deforms. The deformation
per unit length is called strain (
compressive (-). Practical strain values are usually quite small
(typically less than 0.005 inch/inch for most metals) and are often
expressed in micro-strains (
measurements as shown below.
Normal Strain (
of the deformation along the
axis of the applied force.
/ L
Shearing Strain (
of the angular distortion of a
body. It is approximated by the
tangent of the angle formed by
the angular change between two
line segments that were parallel
in the undeformed state.
Poisson Strain (
property of materials known as
the Poisson Ratio. It is the
negative ratio of transverse and
longitudinal normal strain
when a body has a longitudinal
tensile force applied.
ε ∆
where = D / D and
t
Stress Stress is a term used to compare the loading applied to a
material with its ability to carry the load. Stress (
not be measured directly; it must be computed from material properties
and measurable quantities such as strain and force.
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ε
). Strain may be either tensile (+) or
µε
). There are three common types of strain
Force
ε
) is a measure
ε ∆
= L
γ
) is a measure
ν
) measures a
F
∆
D - D
ν ε ε
= - / ,
t
ε ∆
= L / L
Force
(F)
∆
L + L
γ
F
∆
L + L
σ
) in a material can
(F)
F
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