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The characteristic of type- II composite pressure
cylinder with artificial defect by analysis of acoustic
emission parameters
• Hyun-Sup Jee, No-Hoe Ju, Jong-O Lee
• Korea Institute of Materials Science
10. 10. 2011
6th International Workshop NDT in Progress, October 10 – 12, 2011
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Introduction
Gas vehicle in korea
Gas vehicle in the world
LPG : 1.7 million
CNG : 20000
CNG : 10 million
: 50 million (expect 2020)
CNG : ~250bar
H2 : ~ 350bar
New H2 : ~ 700bar
300km
600km
Increased risk.
NDT (periodic inspection) CNG vehicle fuel Tank
Development Inspection Method
Fig. 1. CNG tank exploded in korea (8 case)
□ Experimental Cylinder
▪ Type-ll gas cylinder (64 Liter)
Fig. 2. The shape and dimension of gas cylinder
- liner thickness : 6mm
metal : 34CrMo4 steel plate
- Deep Drawing Ironing
- Operating Pressure : 207bar
Experimental Procedure
B
A
A
B
Liner
Composite
Axial Fiber
Resin Rich Layer
ϕ44
150
70
min. 4.3
R260
R180
min. 6.4
860
C
C
Tape
(width: 50 mm)
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□ Experimental setup
Fig. 3. Schematic diagram of Experimental setup
▪ AE sensor
: Resonance 150 kHZ
R151(PAC)
▪ DiSP-52 AE workstation (PAC)
▪ Threshold : 40 dB
▪ Simulated source
0.5 mm 2H pencil lead breakage
sensitivity 98 dB (1 inch)
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AE Sensor
AE System
Pump &
Controller
Type – ll Gas Cylinder
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□ Fabrication of Artificial Defect
Fig. 4. Schematic diagram of artificial defect
Width 3mm, Depth 3mm , Length 50 mm
Cycles
Operating
Pressure
(207 bar)
Pressure
0 4k 8k 12k 16k 20k
Bursting
10 min holding
□ Method of experiment
Fig. 5. Load sequence during fatigue and fracture test
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Results and Discussion
□ Fatigue Test and AE source Location
The result of source location with cycle for longitudinal defect
Artificial defect position
Final Fractured position
0 cycle
12000 cycle
4000 cycle
16000 cycle
8000 cycle
20000 cycle
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□ Evaluation of Acoustic Emission Signal
Rise time
Fig. 6. Average rise time with cycle for
longitudinal defect and sound cylinder
Sound cylinder
The source in the early stages (0 cycle) are
mostly due to the initiation of matrix crack and
the growth of the created cracks, and in special
cases includes the possibility of growth for the
fatigue crack of liners due to the defects
already existing in the liner at the time of
production.
The average rise time of a sound cylinder in the
first 3 cycles fatigue test in the figure is about
110㎲.
Cylinder with artificial defect
56㎲ and afterwards decreased to 34㎲ after the
8000th cycle and increased to 82㎲ about after
the 12000th cycle and then decreased again.
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Fig. 7. The rise time distribution during
initial 3 cycles for sound cylinder
Clearly distinguished as around 10 ㎲ and over 100 ㎲
The grey mark shows the rise time while load holding
during the three cycles and also at 90 %, which is the
highest, has a rise time of about 10 ㎲.
Growth of an existent crack rather than
initiation of a new matrix crack.
The growth of crack around 10 ㎲.
The rise time of AE signal which occurs during the
initiation of a matrix crack : more than 100 ㎲
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Load holding
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0 cycle
12000 cycle
4000 cycle
16000 cycle
8000 cycle
20000 cycle
The source forms a cluster around the defect The AE source scattered
overall cylinder
300 kHz
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Frequency
0 cycle
12000 cycle
4000 cycle
16000 cycle
8000 cycle
20000 cycle
Frequency by calculation was used because resonant sensors
(By rise time, duration and count) Initial Frequency
Initial Frequency : 100 ~ 200 kHz
(By the initiation and growth of matrix crack)
200 kHz
100 kHz
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Reverberation Frequency
0 cycle
12000 cycle
4000 cycle
16000 cycle
8000 cycle
20000 cycle
150~300kHz : 23 events
16 events (70%) : matrix crack
(Ends of artificial defect) Mean Rev. frequency 73kHz
Cf. Mean Rev. frequency 50~75kHz (Burst test)
Cf. Rev. frequency 150~300kHz (Burst test)
Mean rise time : 31 ㎲
(by growth of matrix crack)
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Amplitude distribution slop
: the slope in the amplitude distribution is known to be related to the mechanism of the source
① (0.04)
② (0.12)
① ②
①
②
①
② ①
②
① ②
0 cycle
12000 cycle
4000 cycle
16000 cycle
8000 cycle
20000 cycle
Growth of Matrix crack
Initiation of Matrix crack
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Analysis of AE signal occurred in the final burst location
①
③ (0.06)
Fig. 8 The amplitude distribution of accumulated
hits in the final burst position
AE signals that occurred in the final burst position, event signals observed around the final burst
location within 200 mm hoop direction in terms of length as marked in Fig. 7 were analyzed. 18
events were occurred during the 20000th fatigue cycle and the number of related hits was 59.
Fig. 9 distribution of rise time of signals occurred
in the final burst position
No rise time above 100 ㎲ and around 10 ㎲
Growth of Matrix crack (Simillar) Initiation and growth of liner crack
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The result of fatigue test
Fig. 10 .longitudinal defect and matrix crack
after 20000 cycles fatigue test
Matrix crack
Artificial defect
(Longitudinal direction)
Figure shows the surroundings of the
longitudinal artificial defect after the
20000th cycle
There is a matrix rupture progressing in
a hoop-direction and although not clear
in the picture
At the end of the depth in the artificial
defect, delaminating was observed on
the overall defect.
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The position of the longitudinal defect was shown well using the identification of
acoustic emission location during the fatigue test and the average rise time of
acoustic emission signal related to events occurring here was about 30 - 90 ㎲ and
signals with a shorter rise time can be observed more in the growth rather than in
the initiation of matrix cracks.
The initial frequency is distributed around 100 ~ 200 kHz
The reverberation frequency higher than 150 kHz are related to the growth of
matrix cracks.
The slope of accumulated amplitude distribution
0.04 : the initiation of matrix cracks
0.12 : the growth of matrix cracks
0.06 : the initiation and growth of liner crack
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Conclusion