The results of acoustic emission (AE) monitoring of the DC-XA composite liquid hydrogen tank are presented in this report. The tank was subjected to pressurization, tensile, and compressive loads at ambient temperatures and also while full of liquid nitrogen. The tank was also pressurized with liquid hydrogen. AE was used to monitor the tank for signs of structural defects developing during the test

Wilkerson, C.

English

NASA Technical Reports Server

NASA Technical Memorandum 108520
Acoustic Emission Monitoring of the DC-XA
Composite Liquid Hydrogen Tank
During Structural Testing
C. Wilkerson
Marshall Space Flight Center ,, MSFC, Alabama
National Aeronautics and Space Administration
Marshall Space Flight Center * MSFC, Alabama 35812
October 1996
https://ntrs.nasa.gov/search.jsp?R=19970001260 2020-06-16T03:50:02+00:00Z

TABLE OF CONTENTS
Page
I. INTRODUCTION ..................................................................................... 1
II. PROCEDURE .......................................................................................... 1
III. TEST RESULTS ...................................................................................... 2
A. Ambient Temperature Tests ...................................................................... 2
B. Cryogenic Temperature Tests .................................................................... 3
IV. CONCLUSIONS ...................................................................................... 4
V. RECOMMENDATIONS .............................................................................. 5
o_o
Ill
LIST OF ILLUSTRATIONS
Figure
1.
2.
3.
Title Page
Cumulative acoustic hits versus pressure (lb/in 2) ................................................ 3
Pressure versus time for the flight operations simulation test .................................. 4
Cumulative acoustic hits versus time for the flight operations simulation test ................ 4
LIST OF TABLES
Table
1.
2.
3.
4.
Title Page
AlE system settings .................................................................................. 1
Test identifiers ....................................................................................... 2
Number of AE hits for ambient temperature tests ................................................ 2
Number of AE hits for liquid nitrogen tests ...................................................... 3
iv
TECHNICAL MEMORANDUM
ACOUSTIC EMISSION MONITORING OF THE DC-XA COMPOSITE LIQUID
HYDROGEN TANK DURING STRUCTURAL TESTING
I. INTRODUCTION
As part of the reusable launch vehicle program, McDonnell Douglas built a composite liquid
hydrogen tank to be used as the flight tank on the DC-XA vehicle. The tank, 8 ft (2.43 m) in diameter and
16 ft (4.88 m) long, underwent structural testing at the Marshall Space Flight Center. Acoustic emission
(AE) monitoring of the structure was included in the monitoring and inspection techniques.
The purpose of using AE during structural testing was to monitor the tank for acoustic indications
of structural damage in two areas: the central joint and the repair area on the forward dome. This test was
also used to establish and verify techniques for using AE on cryogenic fuel tanks.
II. PROCEDURE
A total of 18 AE transducers were bonded to the tank in three areas. All transducers and pre-
amplifiers were manufactured by Physical Acoustics and were bonded with Hysol EA 9394 adhesive.
Sensor and adhesive selection was based primarily on their ability to withstand the thermal environment
that would be encountered during the test. Twelve model $9215 AE transducers were bonded, equally
spaced, to the central joint of the tank. Two $9215's were bonded to the forward dome, 10 inches apart on
either side of the repair area. Also included in this test were four transducers from Rockwell International.
These transducers were used to establish and verify AE techniques as part of Rockwell's effort to develop
a flight AE system that would be incorporated onto the DC-XA. Two model D9215 transducers and a
model PICO transducer were bonded in a triangular array, 10 inches per side, just above the lower Y joint,
where the lower skirt was bonded to the tank. A model Mini-30 transducer was bonded inside the array.
Each transducer was connected to a model 1220A preamplifier with a gain setting of 60 dB. The system
used to collect data was a Physical Acoustics model Spartan AT supported by a PC.
Three location groups were identified: linear location between the two transducers on the dome,
linear location between each pair of transducers around the central joint, and triangular location within the
triangular array above the Y joint. Each transducer was checked by pencil lead break tests to verify that the
transducer was working. Each location group was checked by pencil lead break tests to verify that the
group was locating accurately. The system parameters are described in table 1.
Table 1. AE system settings.
AE Parameters
Peak Definition Time 100 Its
Hit Definition Time 200 Its
Hit Lockout Time
Total System Gain
Threshold
500 Its
60 dB
60 dB
Thestructuraltestswereconductedin threegroups:appliedloadsandpressuresat ambienttem-
erature;appliedloadsandpressuresatcryogenictemperature;andfill, pressurize,anddraintestsusing
quidhydrogen.Table2 showsthetestlabelsfor theambienttemperatureandliquid nitrogencases.For
this test,themaximumexpectedoperatingpressure(MEOP)was53.6lb/in2(36_I.6kPa).Thelimit loadin
tensionwas67,775lbf (301.6kN) andin compressionwas88,560lbf (394.1kN).
Table2. Testidentifiers.
TestIdentifier
A1PT
A2PT
A1PC
A3PC/A4C
C1PC
C3PC
C1PT/C2PT
TestDescription
Ambienttemperature,tensileloadto 40percentlimit, pressureto
40percentMEOP
Ambienttemperature,tensileloadto 110percentlimit, pressureto
140percentMEOP
Ambient temperature,compressiveload to 40 percent limit,
pressureto 40percentMEOP
Ambient temperature,compressiveload to 110 percent limit,
pressureto 140percentMEOP
Liquid nitrogen-filled, compressiveload to 40 percent limit,
pressureto 40percentMEOP
Liquid nitrogen-filled, compressiveload to 140 percentlimit,
pressureto 110percentMEOP
Liquid nitrogen-filled,tensileloadto 110percentlimit, pressure
to 140percentMEOP
III. TEST RESULTS
A. Ambient Temperature Tests
The fwst attempt at ambient temperature testing was conducted with the preamplifier gain set to
60 dB. As the data were being collected, it was apparent that the 60 dB setting was too high. Emissions
from purge lines and other nontest-related sources were being detected, making the data useless. The first
attempt at A1PT ended prematurely, allowing the preamplifier gain to be reset to 40 dB.
The second attempt to complete case A1PT ended when the load lines failed at 36 percent of limit
load and 31 percent of the MEOP. Case A1PT was completed on the third attempt. Testing and AE data
collection proceeded without incident until equipment failure rendered the data from A3PC/A4C useless.
AE hit data for the ambient cases is tabulated in table 3.
Table 3. Number of AE hits for ambient temperature tests.
Test Identifier Number of AE Hits
41558A1PT second attempt
A 1PT third attempt
A2PT
111
31368
A1PC 56
A3PC/A4C Data Lost
Although a large number of acoustic hits were recorded, they were mainly of low amplitude and
short duration. This activity can be attributed to crazing in the resin material. Also, the low number of hits
on the final run of A1PT and on A1PC indicates that the tank is following an AE principle known as the
Kaisereffect.TheKaisereffectstatesthatastructureis acousticallyactiveonly the first time it is loaded to
a given state. The Kaiser effect is not an axiom, but a useful rule of thumb that generally indicates struc-
tural problems when it is not present. The presence of the Kaiser effect in this structure is shown graphi-
cally m figure 1. As the pressure increases, the acoustic activity remains negligible until the pressure
passes the 21 lb/in 2 point, the highest pressure from previous tests.
313G8 4754
154464 694921
DDD HH:MM:S'
8 82:82:88
LOAD #i C_.E--C
-1.48
IF_-
+°ill,ill
l- r'r'I'rVrT'_
HI_ vs CHANNEL
T"J P]_INI' GIIAlq.I
F6 USL'_ COIIIIENT
F'? PBEIJ, GI_APH
]?8 NEXT G]_RPH
F9 SlOP
FIB SlOP
• (CB) = (_EAPH
RE_U:IV END
::DCXATB21.DTA Graph 815 oF 16
D(:-X.q test 12/B6/95 19:43:82
3L_Be- :'--.: .... : .... : .... : .... : .... : .... : .... : .... : .... :
-: .... : .... : .... : .... :.[..: .... : .... : .... : .... i .... :
-i .... i .... ! .... i-. .! .... ! .... i .... i .... i .... _.... il
.!iiiiiiiilli iii!+iiiiiiiiiiiiiiiiiiiiiiill
e , , "'; .... , .... ; .... , .... ; .... ; .... ; .... ;|
B 28 48 £B 88 1BB
HIT'S vs. PgB_I. II(psi)
Figure 1. Cumulative acoustic hits versus pressure (lb/in2).
B. Cryogenic Tests
The cryogenic test series started with a liquid nitrogen fill and drain of the tank with no induced
loads or pressures. The fill generated 13,832 acoustic hits of principally low amplitude and short duration.
The second fill of the tank generated similar results, indicating that the Kaiser effect may not be particularly
useful for evaluating tests performed at cryogenic temperatures. Table 4 shows the AE hits for the liquid
nitrogen and liquid hydrogen tests.
Table 4. Number of AE hits for liquid nitrogen tests.
Test Identifier Number of AE Hits
First liquid nitrogen fill
Second liquid nitrot[en fill
C1PC
13,832
9,435
200,000+
C3PC 200,000+
C 1PT/C2PT No data
Leak Check 19
Despite the large amount of data recorded during this phase of the testing, little can be deduced
from it. The two tests differ from the two fills only in the number of hits. The proportion and distribution
of the hits with respect to amplitude and duration remains similar. Most of the acoustic activity during
C 1PC and C3PC appears to result from interaction of liquid nitrogen with the internal insulation. Each
time the pressure was increased, there was a surge of acoustic activity that continued for some time after
the pressure had stabilized. The most meaningful data from this set are from the leak check that was
performedafterthecompletionof all liquid nitrogentesting.Thetankwaspressurizedto 54 lb/in2,andthe
lackof acousticactivityduringthischeckindicatesstructuralsoundness.
Thelastproceduresperformedwereflight operations imulationsusingliquid hydrogenpressur-
izedto 100-percentMEOP.TheAE's duringthesetestsweresimilarto theemissionsfrom theliquid
nitrogentests.Therewereno indicationsof structuralproblems.Theemissionscontinuedafterthepres-
surestabilized,suggestingthattheactivity resultedfrom theinteractionof liquid hydrogenwith internal
insulation.Figures2 and3 showthisphenomenon.
a_-492 62_
DDD HH:MM:S
• 82:35:5"/
armT;m_ CYCLE-<
15.56
1E4 -
Hl'rS vs C_NN_
F5 P_INT
F6 USER COHI_NT
F'7 PREU. _fU_.t
F8 N£XT G_PH
F_ STOP
FJ.O STOP
g (C)t) = G]thlq.t
REPLAY DID
DC-XA test 12/13/95 1.3:47:11
"" • _-J.... " .... '[_ "':" _1": .... :
-::l::::::::i::::F-:i.,!.......i - !....
.... : .... : .... :. --:- -i:-- -: ....... : .... : .... ',
: : i : : : : 1 :
24.... - .... ----:.--: .-----i---- .... i--- .... -i
D- i-t- I |--T s -_T | a | | i |
IS 21_0 4800 £OOO 8800 tOOOO
Graph g14 of 17 PRRNq. |L(psi) vs. TIHE(sec)C:DCXATO67.DIA
Figure 2. Pressure versus time for the flight operations simulation test.
_m
O il2:3_:57
CVCLE-.C
HITS vs
P21NT _PH
FG USER COPDSENT
17 PREU. GRAPH
T8 NEXT GRRPH
F9 STOP
FJJ9 STOP
ill (CR) = CRRPH
RE_L_Y END
DC-XR test _13/cJ_ _:47:11
....... : .... : .... : .... : . . - • - - : :i
,_.... : .... : .... : .... : .... : .... : .... : .... : .... : .... :,
8- u , v-;_ TTr_:_ : " "
........................... T_.,;,,..;
O 40 6000 _OO 1OOe8
Crapb IL5 _ 17 HITS vs. Tl_(sec)i DCX_TO67 . D_1_
Figure 3. Cumulative acoustic hits versus time for the flight operations simulation test.
IV. CONCLUSIONS
AE gave no indication of damage to the tank at the locations monitored. All transducers withstood
the exposure to low temperatures. The adhesive bonds holding the transducers to the tank also remained
intact,althoughthequestionhasarisenthatsomeof theacousticactivitymayhaveoriginatedin theadhe-
sive.Althoughthebasictechniquesfor performingAE onthis typeof structurewereverified,considerable
work remainsbeforeastandardtechniqueis developed.
*t
V. RECOMMENDATIONS
As a result of data analysis and actual test performance, the following recommendations are made:
1. For AE to provide meaningful test results, a more thorough understanding of the article being
tested is essential. Specific knowledge of the construction techniques and materials used or present in the
structure is required. This could be accomplished by integrating nondestructive evaluation more fully into
the manufacturing and design process.
2. A thorough knowledge of the test plan is essential to properly set up AE monitoring of a test.
Minor modifications to the test plan should be considered to enhance the usefulness of AE data.
3. No structure should be tested without either a data base of previous tests on similar structures
and materials or a series of subcomponent tests leading up to the final structure. The use of AE should be
planned well in advance of the final phase of testing to accommodate this requirement.
4. Further investigation into the use of AE at cryogenic temperatures should be undertaken. Issues
investigated should include thermal effects on piezoelectric sensors, selection of frequency range to moni-
tor, adhesives used to bond transducers, and the characterization of signals taken from a cryogenic
environment.
5
APPROVAL
ACOUSTIC EMISSION MONITORING OF THE DC-XA COMPOSITE LIQUID
HYDROGEN TANK DURING STRUCTURAL TESTING
By C. Wilkerson
The information in this report has been reviewed for technical content. Review of any information
concerning Department of Defense or nuclear energy activities or programs has been made by the MSFC
Security Classification Officer. This report, in its entirety, has been determined to be unclassified.
P.H. SCHUERER
Director, Materials and Processes Laboratory
6

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1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED
October 1996 Technical Memorandum
4. TITLE AND SUBTITLE
Acoustic Emission Monitoring of the DC-XA Composite Liquid
Hydrogen Tank During Structural Testing
6. AUTHOR(S)
C. Wilkerson
7. PERFORMING ORGANIZATIONNAME(S)ANDADDRESS(ES)
George C. Marshall Space Flight Center
Marshall Space Flight Center, Alabama 35812
9. SPONSORING/MONITORING AGENCYNAME(S) AND ADDRESS(ES)
National Aeronautics and Space Administration
Washington, DC 20546-0001
5. FUNDING NUMBERS
8. PERFORMING ORGANIZATON
REPORT NUMBERS
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
NASA TM-I08520
11. SUPPLEMENTARYNOTES
Prepared by Materials and Processes Laboratory, Science and Engineering Directorate.
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Unclassified-Unlimited
12b. DISTRIBUTION CODE
13. ABSTRACT (Maximum 200 words)
The results of acoustic emission (AE) monitoring of the DC-XA composite liquid
hydrogen tank are presented in this report. The tank was subjected to pressurization,
tensile, and compressive loads at ambient temperatures and also while full of liquid
nitrogen. The tank was also pressurized with liquid hydrogen. AE was used to monitor the
tank for signs of structural defects developing during the test.
14. SUBJECT TERMS
Acoustic emission, nondestructive evaluation
17. SECURITY CLASSIFICATION
Unclassi fled
NSN 7540 - 01 - 280 - 5500
18. SECURITY CLASSIFICATION
OF THIS PAGE
Unclassified
19. SECURITY CLASSIFICATION
OF ABSTRACT
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9
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NTIS
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Acoustic Emission Monitoring of the DC-XA Composite Liquid Hydrogen Tank During Structural Testing

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