Engine Titanium Consortium - Center for Nondestructive Evaluation ...

Peak-Noise-to-Signal (% FSH)
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Peak Noise Levels for
Ti 6-4 High Noise Coupons
#1 FBH at 12 dB above 80%
or at 318.5% on this scale
56.6% (3 dB below 80%)
For each specimen,
Rule-of-Thumb would
predict a straight line
passing thru origin.
Slope dependent on FOM
PW8
HW5
GE6
F5 @ 0dB
F5 @ -3dB
F6 @ 0dB
F6 @ -3dB
F8 @ 0dB
1.6 usec time gate
0 100 200 300
Sqrt (Pulse Volume in cubic mils)
#1/2 FBH
approx at 80%
on this scale.
Figure 6. Peak noise vs. pulse volume measurements performed at GE-QTC. PW8, HW5, and
GE6 denote the highest noise coupons cut from three Ti 6-4 forgings.
From Figure 6 one can conclude that choosing the square root of pulse volume to be 240 mils 3/2 or
smaller likely ensures that the peak noise is at least 3 dB below the response from a #1/2 FBH for
the “noisiest” PW and GE coupons. For this choice, the peak noise in the noisiest HW coupon
would be near to but slightly above the 3dB level. If we assume that the typical pulse duration is
equal to 37 mils (average of measured values) the limitation on the beam diameter would be about
( π × ) ⎤
1/2
240 ⎡⎣4 / 37 ⎦ or about 45 mils. Thus, we estimate that a forging inspection which achieves
#1/2 FBH sensitivity, requires a beam diameter that does not exceed 45 mils at any depth within the
region of interest.
Our next objective was to design an inspection that covered 3.2” of material depth using the
minimum number of zones and ensuring that the beam diameter did not exceed 0.045” at any
depth. We note that 3.2” is the maximum depth required to inspect forgings selected for this task
from all OEMs. An optimization procedure was employed to determine the maximum zone size and
to design a transducer for each zone. First the water path was fixed at 3” with the transducer
diameter and focal length treated as unknown “fitting” parameters. Since the entry surface is flat for
this exercise, one needs to consider spherically focused probes only.
The beam diameter for a given transducer at a given depth was calculated using the Gaussian-
Hermite beam model developed by Iowa State University. It was determined that a 7/16”-wide zone
Quarterly Report – January 1, 2002 –March 31, 2002
print date/time: 6/6/2002 - 8:39 AM – Page 63