jun-ichi tomioka , kazuhiro kiguchi, yohsuke tamura, hiroyuki mitsuishi ,

The 4th International Conference on Hydrogen Safety September 18th, 2011Influence of Pressure and

Temperature on the Fatigue Strength of Type-3 Compressed-Hydrogen Tanks for

Vehicles

Jun-ichi TOMIOKA, Kazuhiro KIGUCHI, Yohsuke TAMURA,

Hiroyuki MITSUISHI,

Japan Automobile Research Institute

2

1. INTRODUCTION

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www.peugeot.com

Carbon Fiber Reinforced

Plastic (CFRP)

Aluminum Alloy Liner

35MPa Type-3

35 MPa Compressed Hydrogen Tanks

Type-3 : Fully wrapped composite tanks with metal liners

Type-4 : Fully wrapped composite tanks with plastic liners

“Fuel Cell” or“Hydrogen Engine”

Background 1 – Hydrogen Tank

4

Background 2 – Fatigue Strength Fatigue strength against pressure cycling.

Hydraulic pressure cycle test examination of fatigue life fluid temperature changes slightly 300 cycles per one hour

Gas cycle test examination of fatigue life and hydrogen

embrittlement gas temperature changes greatly 1 cycle per one hour

Pre

ssur

e

Time

Leak...

It is not clear what effect the diferences in the test methods have on the fatigue process.

5

Background 3 – Load on Tank Internal pressure (gas)

Pressure changes with temperature, even if the same mass is filled.

SOC (State of charge) :hydrogen-filled state based on hydrogen-mass in the tank.

Thermal stress Because of differences in

thermal expansion rates, thermal stress is generated by temperature changes.

CFRP thermal expansion:

small

Aluminum Alloy Linerthermal expansion:

large

35MPaType-3

Fatigue life under the SOC100% condition is not

clear

-60-40-20 0 20 40 60 80 1000

1020304050

2835

44

SOC:100%

Temperature [°C]

Pre

ssu

re [

MP

a]

6

Purpose

To clarify the influence of environmental temperature and pressure assuming SOC100% on the fatigue life of compressed hydrogen tanks for vehicles.

Hydraulic pressure cycle tests with varying environmental temperatures and pressures

LT(low temp.) : -40°C, 28MPaRT(room temp.) : 15°C, 35MPaHT(high temp.) : 85°C, 44MPaAT(ambient temp.) : 15°C ~25°C, 44MPa

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2. MATERIALS AND METHOD

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Specification of Test Tank

Specification

FillingPressure [MPa]

Volume

[L]

External Diameter

- Length [mm]

Liner Material

Type-3 35 28 F280 – 730 Aluminum Alloy

Schematic Diagram of Compressed Hydrogen Tank

Carbon Fiber Reinforced Plastic (CFRP) Layer

Liner

Tail End PlugCylindrical Section

Dome 　Section

Specification of Test Tank

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Thermostatic Chamber

Constant-temperature

(-40 ~ 150 deg.C)

High pressure pipe

Pump

Test Equipment – Hydraulic Tester

120 MPa Intensifier

Thermostatic Chamber

Intensifier

Power Unit

hydraulic Tester

10

0

10

20

30

40

50

Pres

sure

[M

Pa]

-40℃28MPa

15℃35MPa

85℃44MPa

Test Conditions

Pressure profile of cycle test

Test conditions of pressure cycle test

　 LT RT HT AT*

SOC 100% 125%

Temperature -40°C +15°C +85°C +15~25°

CMaximumPressure 28MPa 35MPa 44MPa 44MPa

MinimumPressure 0 MPa

Fluid(Medium)

Perfluoro-

polyether

Deionized Water

Frequency 15 sec/cycle

Waveform Sine Curve

TerminationOccurrence of Leak Before Break

(LBB) 　* Ambient-Temperature Pressure-Cycle Test specified in JARI S001

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3. RESULTS OF CYCLING TESTS

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Fatigue Life of Type-3 Tank

Leakage occurred in all tanksLives under SOC 100% were longer than the life under

AT(SOC125%). →Pressure-cycle test under AT(SOC125%) can ensure the safety of a Type-3 tank against fatigue.

LT:-40℃28 MPa

SOC100%

RT:15℃35 MPa

SOC100%

HT:85℃44 MPa

SOC100%

AT:15~25℃44 MPa

SOC125%

10,000

100,000

1,000,000

135,626 147,797

27,645 22,782

Fati

gu

e L

ife [

cycle

s]

Fatigue life determined by hydraulic pressure-cycle tests

SOC100% the mean ± S.E., N=2

Leak Leak

Leak Leak

SOC125%

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4. DISCUSSION

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Liner Stress of Type-3 tank

To determine the liner stress, we measured the strain on the inner surface of the liner.

①Stress due to internal pressure (tensile stress)

②Residual stress Autofrettage processing produces residual stress

(CFRP: tensile stress, Liner: compressive stress) ③Thermal stress

Because of differences in thermal expansion rates in aluminum alloy and CFRP

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①Stress due to Internal Pressure

Strain gauge on the liner

Hydraulic

system

Hydraulic pressure

Measuring method for strain due to internal pressure

The inner surface of the liner

Strain gauges were attached to the inner surface of the liner

Applying pressure to the tank

Measuring the strain due to internal pressure

Caluculate the stress based on the measured strain.

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①Stress due to Internal Pressure

Relationship between pressure and stress of the liner

Relationship between pressure and stress of the liner was linear-proportion.

0 10 20 30 40 500

50100150200250300350400450

circumferential stressaxial stress

Pressure [MPa]

Lin

er

str

ess [

MP

a]

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②Residual Stress

Measuring method for residual strain

A, B : Outer surface of CFRPa, b : Inner surface of liner

ＢＡ

Strain gauges

Cut 1 Cut 2

a

b

Strain gauges

Cut 3 : Separate CFRP and LinerCFRP

Liner

ＡabB

In all tanks after the pressure-cycle test, strain gauges attached to the outer surface of the CFRP and the inner surface of the liner

Cutting the tank at room temperature (15°C) to release the residual strain

Measuring the residual strain Caluculate the stress based on the measured strain.

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②Residual Stress (Measured results)

Residual stress of the liner after pressure-cycle test at HT was smaller than the others.

Usageenvironment

Liner circumferential

stress

LT : -40°C -256MPa

RT : 15°C -239MPa

HT : 85°C -126MPa

Residual stress of Liner

Axialstrain

Circumferentialstrain

CFRP 0.097% 0.034%

Liner -0.134% -0.265%

Residual strain of the tank after the pressure-cycle test

at RT

Tensile strain resided in the CFRP and compressive stress resided in the liner.

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③Thermal StressThermostatic

Chamber

Aluminum tube

-40°C ～ 85°CThermocouple

Strain gauge

εts = ε1 - ε2

εts: Strain due to the thermal stressε1 : Strain of the liner

ε2 : Strain of the aluminum tube

ε1 ε2

Strain gauges and thermocouples were attached to the inner surface of the liner and the aluminum tube

Changes in the temperature ranging from -40°C to +85°C(①15°C→②-40°C→③15°C→④85°C→⑤15°C ）

Measuring the thermal strain Caluculate the stress based on the measured strain.

Measuring method for thermal strain

Thermocouple

Strain gauge

20

-50 0 50 100 -400

-300

-200

-100

0

Temperature [°C]

Lin

er

Str

ess [

MP

a]

Relationship between temperature and circumferential stress of the liner

In high-temperature and low-pressure, the liner was loaded with residual compressive stress and compressive stress due to the thermal stress.→The liner was deforemd plastically in high-temperature and low-pressure.

plastic deformation(yield stress: 300MPa)

③Thermal Stress

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Liner Stress (hydraulic cycle)

-50 -30 -10 10 30 50 70 90-400

-300

-200

-100

0

100

200

SOC0%

SOC100%

SOC125% at 20°C

Temperature [°C]

Lin

er

Str

ess [

MP

a]

Relationship between temperature and circumferential stress of the liner

Tensile stress at AT (SOC125%) exceeds that under any SOC100% condition.

⇒The pressure-cycle test under AT can ensure the safety of a Type-3 tank against fatigue life.

plastic deformation(yield stress: 300MPa)

LT -40°C,28MPa HT

85°C,44MPa

AT ( 15~25°C, 44MPa )

RT15°C,35MP

a

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-50 -30 -10 10 30 50 70 90-400

-300

-200

-100

0

100

200

SOC0%

SOC100%

inferred SOC100% in gas cycle

Temperature [°C]

Lin

er

Str

ess [

MP

a]

Liner Stress (gas cycle)

Relationship between temperature and circumferential stress of the liner

gas cycle

at -40°Cgas

cycleat 15°C

the gas cycle is the repetition of a low-temperature and low-pressure condition and a high-temperature and high-pressure condition.

→The liner will be not deforemd plastically in gas cycle.

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-50 -30 -10 10 30 50 70 90-400

-300

-200

-100

0

100

200

SOC0%

SOC100%

inferred SOC100% in gas cycle

Temperature [°C]

Lin

er

Str

ess [

MP

a]

Liner Stress (hydraulic and gas)

Relationship between temperature and circumferential stress of the liner

gas cycle

at 15°C

The stress range during gas cycles is smaller than during hydraulic cycles.

⇒Hydraulic cycles are more severe than gas cycles.

LT -40°C

HT85°C

RT15°C

gas cycle

at -40°C

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5. SUMMARY

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Summary

Pressure cycle tests assuming SOC 100% in type-3 tanks revealed that The fatigue life assuming SOC 100% is longer

than the room temp. pressure cycle test (AT,SOC125%).

The room temp. pressure cycle test (AT,SOC125%) can ensure the safety of a Type-3 tank against fatigue.

Stress range during gas cycles is smaller than during hydraulic cycles, so the hydraulic-cycle tests are more severe than gas-cycle tests.

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THANK YOU

This study is summarizes part of the results of "Establishment of Codes & Standards for Hydrogen Economy Society - Research and Development Concerning Standardization of Hydrogen and Fuel Cell Vehicles" consigned by the New Energy and Industrial Technology Development Organization (NEDO).