134 6. EXAMPLE PRACTICAL PROCEDURES AND RESULTS
are no significant disturbances in stress distributions close to the surface; the linear or uniform
stress distributions extend from the sub-surface material to the surface.
C
C
B
B
(a)
(b) (c)
150
100
50
0
-50
-100
-150
150
100
50
0
-50
-100
-150
0
Depth 400 µm 800 1200 1600 2000
0 Depth 400 µm 800 1200 1600 2000
B
C
B
C
Distributions of meridional* stresses vs. depth
Distributions of circumferential* stresses vs. depth
Residual Stresses MPaResidual Stresses MPa
Figure 6.12: Aluminium alloy block sample, gauge installation, and stress distributions (images
courtesy of Stresscraft Ltd.).
While hole drilling in this type of material presents no special challenge in terms of hard-
ness, etc., the selection of drilling cutters and drilling parameters must be carefully controlled
to avoid burring at the lip of the hole and the consequent disturbance to the near-surface stress
field. It can be seen that this effect has been avoided in the stress distributions shown. As noted
in the previous example, specimens of this type can be useful to demonstrate that the hole can be
drilled without producing any drill-related artifacts. In this case, the linearity (or uniformity) of
the stress distribution (or at any rate, the absence of significant discontinuities) can also provide
useful confirmation of the performance of the stress calculation method, which is not addressed
by the results from the low-stress sample.
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