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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