Acoustic emission source location of type- II composite
pressure vessel with artificial defect
Hyun-Sup Jee, No-Hoe Ju, Jong-O Lee
Korea Institute of Materials Science
10. 10. 2011
VIth 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 (expected 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
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- 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)
□ 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
□ 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
Results and Discussion
□ Burst Test
Defect type ID Burst pressure
(bar) Remark
Longitudinal A 590
Source
Location
B 610 -
Transverse C 605
Source
Location
D 590 -
Sound E 605 -
F 615 -
Table 1. The burst pressure by defect type
The burst pressure is
590~615 bar with the
difference in the pressure
of the cylinder were
within 5 % and thus was
irrelevant to the existence
of defects.
Fig. 6. position of burst and artificial defect :
a) longitudinal, b) transverse
a b
Artificial
defect position
Artificial
defect position
(Opposite)
we can not precisely know how much the
depth of the defect has to be in order for
the final burst pressure to change;
however, the direction of the defect and
the final burst location do have a
correlation and we can infer that the
longitudinal defect has a bigger effect on
the final burst location.
□ Fatigue Test and Acoustic Emission Test
Fig. 7. The number of hits per channel
during fatigue test for artificial defect (A, C)
and sound (E) fuel tank
Fig. 8. The number of events during
fatigue test for artificial defect (A, C)
fuel tank
Longitudinal defect
4000 cycles ; 41.8 % (events / hits)
8000 cycles ; 55.7 % (events / hits)
Fig. 9. The ratio of events / hits per sensor during fatigue
test for artificial defect (A, C) fuel tank
This is a figure that shows the % of
the number of hits that can precisely
show the source among the total
number of hits
□ Identification and Verification of AE Location
Fig. 10. The elastic wave velocity
with degree between propagation
and wrapping direction
the speed of longitudinal elastic wave : 4512 m/sec
the speed of wrapped direction : 5689 m/sec
Anisotropic cylinder source location method
Fig. 11. source location confirm
□ Fatigue Test and Location of Artificial Defect
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
The result of fatigue test
Fig. 12 .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.
Cylinder with two types of artificial defects (longitudinal and transverse) and a sound cylinder was put in 20000 fatigue test and the pressure was continuously increased and then was burst, the burst pressure was 590~615bar and the differences in pressure on the cylinder were less than 5% and was not relevant to the existence of defects.
There is a correlation between the direction of defect and the final burst location and the longitudinal defect had a greater effect on the final burst location of the cylinder rather than the transverse defect.
Acoustic Emission Signal, which occurs during the fatigue test, occurred more in cylinder with defects rather than in sound cylinder, and as the number of fatigue test accumulated, the number of hits increased more in cylinder with longitudinal defects than in those with transverse defects.
In the case of cylinder with longitudinal defects, events were clustered around the artificial defect and more than 50% of the occurred hits were signals that were related to artificial defects and the source location was precisely found on the defect.
The thickness of the whole cylinder area became thinner like the length of the defect and thus was weaker than other areas of the cylinder. And the final burst was at the location in which the fatigue rupture of the steel liner occurred.
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Conclusion