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The most widely used practical technique for
determining residual stresses is the hole-drilling
strain gage method described in ASTM Standard E837.
With this method, a specially configured strain
gage rosette is bonded to the surface of the test
object; and a small, shallow hole is introduced
into the structure, through the center of the gage,
using a precision drilling apparatus. Strains in
the immediate vicinity of the hole are measured,
and the relaxed residual stresses are computed from
these measurements. The general theory of making
residual stress measurements is covered in Vishay
Measurements Group Tech Note TN-503,
Measurement
of Residual Stresses by the Hole-Drilling Strain
Gage Method
, and the requisite hardware is described in
Bulletin 304,
Strain Gages
and Instrumentation for Residual Stress
Measurements
.
Construction
All gages are constructed of
self-temperature-compensated
foil (06 and 13 S-T-C) on a flexible polyimide
carrier, and incorporate a centering target for use
with a precision milling guide.
EA-Series
(A-Alloy)
gages are available "open-faced" or with
solder dots and encapsulation (
Option SE
);
CEA Series
(A-Alloy)
gages have encapsulated grids, and rugged,
copper-coated sloder tabs. Construction of the N2K
Series
(K-alloy)
is similar to the
N2A Series
and includes copper pads (DP) on the solder tabs.
The
062UM
gage permits installation adjacent to weldments
and intersecting surfaces.
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Vishay Measurements Group
030 Patterns
