Basic Surface Preparation
Operations and Techniques
Gage-Location Layout Lines
The normal method of accurately locating and
orienting a strain gage on the test surface is to
first mark the surface with a pair of crossed
reference lines at the point where the strain
measurement is to be made. The lines are made
perpendicular to one another, with one line oriented
in the direction of strain measurement. The gage is
then installed so that the triangular index marks
defining the longitudinal and transverse axes of the
grid are aligned with the reference lines on the test
surface.
Burnishing Layout Lines
From
VideoTech
Library
VS-101
The reference, or layout, lines should be made with
a tool which burnishes, rather than scores or
scribes, the surface. A scribed line may raise a burr
or create a stress concentration. In either case,
such a line can be detrimental to strain gage
performance and to the fatigue life of the test part.
On aluminum and most other nonferrous alloys, a
4H drafting
pencil
is a satisfactory and convenient burnishing tool.
However, graphite pencils should never be used on
high-temperature alloys, where the operating
temperature might cause a carbon embrittlement
problem. On these and other hard alloys, burnished
alignment marks can be made with a ballpoint pen or a
round-pointed brass rod. Layout lines are ordinarily
applied following the abrading operation and before
final cleaning. All residue from the burnishing
operation should be removed by scrubbing with
M-Prep
Conditioner A
as described in the following section.
Page 12 of 23
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Vishay Measurements Group