Appeal No. 2002-2148 Page 6
Application No. 09/627,143
chordwise direction between a leading edge LE and a trailing edge TE of the airfoil. A
pressure side 46 of the airfoil 34 faces in the general direction of rotation and a suction
side 48 is on the other side of the airfoil and a mean-line ML (see Figure 4) is generally
disposed midway between the two faces in the chordwise direction.
The compressor blade has a tip section 50 that extends along the tip 38 of the
airfoil 34 from the leading LE to the trailing edge TE. The airfoil 34 is subject to
vibrations generated during engine operation and the tip damage 52 operate as high
cycle fatigue stress risers producing additional stress concentrations around them.
Mannava teaches (column 4, lines 40-52) that
[t]his stress may be due to excitations of the blade in chordwise bending modes
commonly referred to as "stripe modes". The dominant failure mode at the blade
tip 38 may not always be the maximum stress mode but rather a lower stress
mode or combination of modes that exist for longer durations over the engine's
mission. By way of example, the predetermined nodal line 59 at the blade tip 38
illustrated in FIG. 2 corresponds to excitation at N PR (Per Rev or Per
Revolution) of the engine's rotor where N corresponds to the number of
compressor vanes 8A in front of or behind the blade. The tip damage 52 located
in this area of the blade tip 38 has the greatest potential for failing the blade
under these excitations.
The tip section 50 includes a predetermined first width W1 such that the tip section 50
encompasses any burrs 52 that may occur along the tip 38 of the airfoil 34.
To counter fatigue failure of portions of the blade along possible crack lines that
can develop and emanate from the burrs along the blade tip 38 at least one and
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