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