Jun-ichi TOMIOKA , Kazuhiro KIGUCHI, Yohsuke TAMURA, Hiroyuki MITSUISHI ,

1. The 4th International Conference on Hydrogen Safety September 18th, 2011 Influence 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

3. Background 1 – Hydrogen Tank 35MPaType-3 Aluminum Alloy Liner “Fuel Cell” or “Hydrogen Engine” Carbon Fiber Reinforced Plastic (CFRP) 35 MPa Compressed Hydrogen Tanks Type-3 : Fully wrapped composite tanks with metal liners Type-4 : Fully wrapped composite tanks with plasticliners www.peugeot.com

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

5. Background 3 – Load on Tank 35MPa Type-3 Aluminum Alloy Liner thermal expansion: large • 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 Fatigue life under the SOC100% condition is not clear

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, 28MPa • RT(room temp.) : 15°C, 35MPa • HT(high temp.) : 85°C, 44MPa • AT(ambient temp.) : 15°C ~25°C, 44MPa

7. 2. Materials and Method

8. Carbon Fiber Reinforced Plastic (CFRP) Layer Liner DomeSection Tail End Plug Cylindrical Section Specification of Test Tank Specification of Test Tank Schematic Diagram of Compressed Hydrogen Tank

9. Test Equipment – Hydraulic Tester hydraulic Tester High pressure pipe Thermostatic Chamber Intensifier Pump Power Unit Thermostatic Chamber 120 MPa Intensifier Constant-temperature (-40 ~ 150 deg.C)

10. Test Conditions Test conditions of pressure cycle test Pressure profile of cycle test * Ambient-Temperature Pressure-Cycle Test specified in JARI S001

11. 3. Results of cycling tests

12. Fatigue Life of Type-3 Tank the mean ± S.E., N=2 SOC100% SOC125% Leak Leak Leak Leak Fatigue life determined by hydraulic pressure-cycle tests • Leakage occurred in all tanks • Lives 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.

13. 4. discussion

14. Liner Stress of Type-3 tank • 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 To determine the liner stress, we measured the strain on the inner surface of the liner.

15. ①Stress due to Internal Pressure Strain gauge on the liner Hydraulic pressure Hydraulic system Measuring method for strain due to internal pressure • 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. The inner surface of the liner

16. ①Stress due to Internal Pressure Relationship between pressure and stress of the liner • Relationship between pressure and stress of the liner was linear-proportion.

17. ②Residual Stress Cut1 Cut 3 : Separate CFRP and Liner Cut2 a Ａ a Ａ CFRP Liner Ｂ b B b Strain gauges Strain gauges A, B : Outer surface of CFRP a, b : Inner surface of liner Measuring method for residual strain • 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.

18. ②Residual Stress (Measured results) 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. Residual stress of Liner • Residual stress of the liner after pressure-cycle test at HT was smallerthan the others.

19. ③Thermal Stress Thermostatic Chamber -40°C～85°C Thermocouple Thermocouple ε1 ε2 Strain gauge Aluminum tube Strain gauge εts: Strain due to the thermal stress ε1: Strain of the liner ε2: Strain of the aluminum tube εts = ε1 - ε2 Measuring method for thermal strain • 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.

20. ③Thermal Stress plastic deformation (yield stress: 300MPa) 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.

21. Liner Stress (hydraulic cycle) AT ( 15~25°C, 44MPa) LT -40°C, 28MPa RT 15°C, 35MPa HT 85°C, 44MPa plastic deformation (yield stress: 300MPa) Relationship between temperature and circumferential stress of the liner • Tensile stress at AT (SOC125%) exceeds that under any SOC100% condition. • ⇒The pressure-cycle test underAT can ensure the safety of a Type-3 tank against fatigue life.

22. Liner Stress (gas cycle) gas cycle at -40°C gas cycle at 15°C Relationship between temperature and circumferential stress of the liner • 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.

23. Liner Stress (hydraulic and gas) gas cycle at -40°C LT -40°C RT 15°C HT 85°C gas cycle at 15°C Relationship between temperature and circumferential stress of the liner • The stress range during gas cycles is smaller than during hydraulic cycles. • ⇒Hydraulic cycles are more severe than gas cycles.

24. 5. Summary

25. 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.

26. 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).