decreasing as we approach the trailing edge,
where the difference between the experimentally
determined displacements from holograms and
those obtained from finite element analysis of
the airfoil reaches 20%.
In the second phase of the study, deflections
of airfoil No. I due to torsional load were
studied. A typical fringe pattern, obtained
during reconstruction of a hologram recording
deflections of airfoil No. 1 due to losd in-
crease of 11.7 in-ibs is shown in Fig. 10.
Again, a series of double-exposure holograms
were recorded, one for each increment in tor-
sional loading, and every hologram was ana-
lyzed using the least-squares method as des-
cribed above. The experimental results ob-
tained from holograms are presented in Figs
ll and 12; in these figures, the coordinates
of the airfoil were nondimensionalized with
respect to the local cord. Results of Figs.
11 and 12 clearly show that the maximum dis-
placements, for a torsion load applied at tip
of the blade, occured at the leading edge.
Unfortunately, there were no corresponding
results from the finite element analysis of
the airfoil available for the comparison.
Finally, airfoil No.2 was subjected to simi-
lar loading conditions as those exerted upon
airfoil No. 1, and Figs 13 and 14 show typi-
cal fringe patterns obtained during recon-
structions of the corresponding holograms.
In particular, Fig. 13 represents airfoil No.
2 acted upon by a tensión load whereas Fig.
14 shows the same airfoil in torsion. Care-
ful examination of these figures reveals an
abrupt change in fringe pattern in the root
area of the blade, indicating high stress
concentrations and a possible failure, at
that place, while in operation. This obser-
vation necessitates further investigation of
airfoil deflections due to different loads in
order to improve the design and, therefore,
to eliminate conditions welcoming failure.
Based on the results presented in this paper,
one can clearly see that the holographic meth-
od of airfoil analysis is a very useful tech-
nique for accurate and precise studies of air-
foll deflections. Holography is complementa-
ry to the finite element technige because it
uses an actual object with the entire spec-
trum of its characteristics, whereas the the-
oretical method greatly relies on the accuracy
of the input parameters such as: geometry,
material properties, loading conditions, bound-
ary conditions, etc. characterizing the stud-
led airfoil. Furthermore, finite element
analysis could not be run without the input of
boundary conditions from holographic analysis
of the tested airfoil which were supplied, in
this study, from data obtained at level 26,
see Fig. 8. As such, hologram interferometry
constitutes a powerful tool for analysis of
airfoils and other jet engine components,
heretofore unobtainable using other techniques.
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i. Dhir, S. K., and Sikora, J. B., "in im
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25
Seiammarella, C. A., and Gilbert, J. A.,
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Pryputniewicz, R. J., "Holographic Analysis
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