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C H A P T E R 6
Example Practical Procedures
and Results
“Operator skill has been identified as probably the most important factor in achieving a reliable
and quality measurement.”
National Physical Laboratory Measurement Good Practice Guide No. 53 (2006).
is chapter describes practical examples of strain gauge installations to illustrate further aspects
of the Hole-Drilling Method. Sections 6.1–6.5 describe examples of rosette installations on
specimens in practical engineering situations. Sections 6.6–6.10 go on to present and discuss
further examples of residual stress measurements on a range of different types of specimens.
6.1 SPECIMEN GEOMETRY AND STRAIN GAUGE
SELECTION DETAILS
ASTM Standard Test Method E837 for hole-drilling describes the required characteristics of
an ideal test specimen. e measurement location on such a specimen has a plane smooth surface
that is remote from any obstacles, edges, or discontinuities such as holes or steps. In addition,
the specimen material is linear-elastic, isotropic and homogeneous.
It is convenient to express the dimensions of specimens as multiples of the mean gauge
diameter D. is is the pitch diameter of the gauge elements set around the target center. e
ideal specimen surface is flat, but curvatures with radii down to 2.4D can be accommodated
with little impact on the results. Another important property of the specimen is the material
thickness in the area of measurement. For specimens to be subjected to through-hole drilling
measurements, ASTM E837 lists the maximum thickness as 0.2D for Type A and Type B
gauges and 0.24D for the Type C gauge. For blind hole (incremental) drilling, the minimum
thickness is 1.0D for Type A and Type B gauges and 1.2D for the Type C gauge.
Figure 6.1 shows the layouts and key dimensions of the widely used Type A and Type B
strain gauge rosettes. Table 6.1 summarizes the geometrical requirements for specimen thick-
ness, distance from adjacent features and surface shape. e main specifications in the table
derive from the ASTM E837, with some additional suggestions based on the practical experi-
ence of the authors.