Improving aircraft composite inspections using optimized reference standards Page: 10 of 13
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Material in/ps Density Impedance Relative
(mm/ps) cm3 gcm2-ps Attenuation'
Carbon Graphite 0.1218 1.589 0.488 -
Boeing Std ST8870 (3.070)
Carbon Graphite 0.1150 1.589 0.463 -
Boeing Std ST8871 (2.912)
Fiberglass (50 V%) 0.1150 1.917 0.605 20 dB (0.2" th)
(2.912) 30 dB (0.5" th)
Boron-Epoxy (50 V%) 0.1310 1.920 0.639 Not
Ivory 0.1185 2.170 0.653 Not
Hysol Potting 0.1010 1.518 0.390 10 dB (0.2" th)
Material EE4183 (2.562)
Phenolic 0.1100 TBD TBD 12 dB (0.2" th)
[United Airlines supply] (2.873) 18 dB (0.5" th)
Phenolic G7 0.0834 1.700 0.358
Phenolic G9 0.1474 1.950 0.727
Phenolic G10 0.1193 1.850 0.559 4 dB (0.2" th.)
Maeil.141) __ 541___ Measured
Phenolic LE 0.1047 1.320 0.350
Phenolic XXX 0.1071 1.300 0.352
Zero Impedance 0.0843 1.240 0.2655 Not
Material (2.141) Measured
Generic Material 0.1150 1.6 -1.8 0.48 -0.54 < 10 dB
* As compared with Boeing step wedge S-
Boeing step wedge ST8871, 0.5" th.
'8870, 0.2" th. and
Table 2: Important Material Properties for Candidate
Laminate Standard Materials
2. Pulse-Echo Ultrasonics - Measurements were made
using a Quantum device in order to study the ability
of P-E UT to resolve the full array of thicknesses in
the laminate standard. Using 1 MHz, 2.25 MHz, and
10 MHz transducers it was possible to resolve
thickness areas from 0.010" to 1.0". Since this is a
velocity-based method, the close match between the
G11 (2.93 mm/ps), carbon (2.90 mm/ps), and
fiberglass (2.91 mm/ps) velocities should eliminate
the need for any conversion factors when using the
generic (G11) material.
3. Resonance (Bondmaster) Test Procedure - A
number of different resonance inspection tests were
conducted in order to relate the response curves
between the G11 candidate material and existing
composite laminate standards. Resonance
inspections were also carried out on a set of three
similar carbon graphite (plain weave) step wedge
specimens which were produced by United Airlines'
composite shop. The resonance tests were
performed to study the degree of spread (variation)
in the response curves for supposedly similar
specimens. This gives us some perspective when
assessing the spread between G11, carbon, and
Resonance response curves were obtained for high
frequency (314 KHz) and low frequency (156 KHz)
inspections over a range of high (12 - 14 dB),
medium (9-10 dB), and low (6-7 dB) gains. High
frequency inspections were used to measure the
Bondmaster response over the thickness range of
0.010" to 0.250" while low frequency inspections
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Roach, D.; Dorrell, L.; Kollgaard, J. & Dreher, T. Improving aircraft composite inspections using optimized reference standards, article, October 1, 1998; United States. (https://digital.library.unt.edu/ark:/67531/metadc711418/m1/10/: accessed May 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.