Residual stresses are the
stresses that remain after external loading has been removed. Any deformation
or annealing process can generate residual stresses. The total stresses on a component are the sum
of residual and applied stresses.
Compressive stresses (negative)
are generally desirable as they typically increase fatigue life and inhibits
stress corrosion cracking while tensile stresses (positive) adversely affect
the performance of a component.
hole-drilling process is the same as for incremental hole-drilling with strain
gages. However, the effect of the material removal is measured optically using
ESPI. No strain gages have to be applied. Prism takes digital images of the
area around the hole while it is illuminated with laser light
instrument acquires digital images from the hole area before and after each
hole-drilling increment. The images are first analyzed for surface
displacements. The pattern of displacements is then directly correlated to
works for any solid material, not only for crystalline ones. It measures the
composite effect of multi-phase materials rather than stresses of a specific
phase. Hole-drilling can cover greater depths in shorter times since
electro-polishing is relatively time-consuming.
to apply strain gages can make a measurement much faster and making multiple
measurements is usually quite easy. Such verification measurements can be
important because the hole-drilling technique itself does not provide a lot of
information on measurement quality.