CRYOGENIC MATERIAL TESTING€¦ · CRYOGENIC MATERIAL TESTING SPECIAL REQUIREMENTS FOR TEST SETUP AND TEST PERFORMANCE DEMONSTRATED ON ADDITIVE MANUFACTURED LIGHTWEIGHT ALLOYS Christoph

where Analysis and Test meet

CRYOGENIC MATERIAL TESTING SPECIAL REQUIREMENTS FOR TEST SETUP AND TEST PERFORMANCE DEMONSTRATED ON ADDITIVE MANUFACTURED LIGHTWEIGHT ALLOYS

Christoph Zauner

KRP Mechatec GmbH where Analysis and Test meet

Index

• Demand of cryogenic testing

• Cryogenic temperature ranges and cooling methods

• Building cryogenic test setups

– Material

– Design

• Performing cryogenic tests

• Example(s)


Demand on cryogenic testing

• Space:

– liquid propellant tank structures (20K for LH)

– cryogenic instruments

• Fusion Research:

– superconducting magnet structures (4K)

• Automotive

– liquid hydrogen tank structures

• Goal:

– material characterisation

– component / structure verification


Temperatures and cooling methods

• Overview on typical temperature ranges, cooling methods and cooling equipment

Temperature Method Equipment

“hot” to -140°C (-180°C)

evaporative cooling of liquid nitrogen

thermal chamber

-196°C (77K) direct immersion in liquid nitrogen

test dewar

-196°C to -263°C (10K)

evaporative cooling of liquid helium

helium dewar gas phase

-269°C (4K) direct immersion in liquid helium

helium dewar liquid phase


Cooling Fluids

• Comparison of Nitrogen and Helium

Temperature Nitrogen Helium Ratio He /

N2

Temperature -196°C / 77K -263°C / 4K -

Density liquid in kg/L 0,8076 0,1785 0,22

Heat of vaporisation in kJ/kg

199 21,1 0,11

Cost per liter in € 0,1 3 30

Cost per cooling 1kg stainless steel to liquid

temperature in € 0,06 108 1677

Delivery by truck stored

in big tanks On-site helium

liquefier

Gas recoverage not required strongly

recommended


Thermal chamber (RT to -140°C)

• „+”

– Wide temperature range, and integrated easy control

– Feedthrough of fixed and moving test machine interface

• „-“

– Limited cryogenic range (commercial -140°C, self build to -180°C)


Direct immersion in liquid nitrogen

• „+”

– High cooling rate

– Flexible cryostat design

• „-“

– Fixed temperature

– Risk of thermoelastic damage of the test setup / test machine during cooling down


Evaporation of liquid helium

• „+” – Wide temperature

range (77K to ~10K)

• „-“ – Temperature gradient

along specimen needs to be compensated by electrical heating

– Low cooling rate

– High Cost

– Temperature Control and LHe flow control required


Direct immersion in liquid helium

• „+”

– Lowest cryo-temperature

• „-“

– Fixed temperature

– Risk of thermoelastic damage during cooling down

– High cost

– Baffle system required


Cryogenic test setups - Materials

• Stainless steel is mainly used

– Low embrittlement and thus robust against transient forces during specimen failure

– Low thermal conductivity (good isolation of load bearing parts)


Cryogenic test setups - Design guidelines

• Mechanical design – “mass is money” at LHe!

– FEM to identify load paths and optimize w.r.t. mass (morphological optimization)

– Assess maximum load capacity of test setup at different temperatures (w.r.t. temperature depended yield strength)

– Take care not to overload stainless steel setups at RT or high temperature


Cryogenic test setups - Design guidelines

• Thermal design

– FEM to identify temperature distribution and achievement

– Evaluate cooling time and cost per test


Cryogenic setups – Vacuum environment

• Low convective heat transfer

• Two axis friction test 2MN/2MN at -190°C under vacuum – vacuum sealing in

cryogenic temperature: CF flanges

– Internal and external cooling of load bearing paths

LN2 tank fixed 4200l

LN2 tank mobile 100l

N2

LN2-outlet

LN2

LN2 – indirect cooling

vacuum chamber direct

cooling channels

NSE Interface

• Heat transfer coefficient from 150°C to 250°C at 50kN


Cryogenic test performance

• Select temperature compatible strain gauges, extensometers and temperature sensors

• Protect test machine from condensed water

• Monitor oxygen in test lab • Take into account liquid

oxygen and liquid hydrogen • Provide gaps for different

thermal expansions • Don’t block test machine

during cooling down and heating up – high risk of overload and destruction

Vetronit Isolation

Protective Foil

Stiffness Temperature

CTE


Application example – 3D printed metals

• Test setup design

– Tension

– Compression

– Shear

– Pin Bearing



• Temperature levels

– RT

– 200K (-73°C)

– 77K (-196°C)

– 4K (-269°C)



• Test performance

– Cooling down

– Strain control during yield

– Switch to stroke control after Rp0.2 has been reached

– Retract extensometer

– Load until failure

0 0.005 0.01 0.0150

100

200

300

400

500

600

Strain [mm/mm]

Str

ess [

MP

a]

Stress vs Strain - Extensometer

Et= 78305 MPa R square=0.9999

TYSt= 557 MPa TYS

u= 538 MPa

TUSt= 591 MPa TUS

u= 571 MPa

e=10.5%

0 200 400 600-80

-75

-70

-65

-60

Time [s]

Tem

pera

ture

[°C

]

T specimen top

T specimen bottom

Limits

0 1 2 3 40

100

200

300

400

500

600

Stroke [mm]

Str

ess [

MP

a]

Stress vs Crossheadtravel

0 10 20 30 400

1

2

3

4x 10

-4

Time [s]

Str

ain

rate

[s-1

]

Strain rate history

0 200 400 6000

1000

2000

3000

4000

5000

6000

7000

8000

Time [s]

Forc

e [

N]


• Keep in mind: Safety first

• Thank you for your attention!

• Questions?


Further Cryogenic Test Examples


Further Cryogenic Test Examples

2MN 900kN

Leakage test of LN2 cryostat

Two axis cryogenic loading test

CRYOGENIC MATERIAL TESTING€¦ · CRYOGENIC MATERIAL TESTING SPECIAL REQUIREMENTS FOR TEST SETUP AND TEST PERFORMANCE DEMONSTRATED ON ADDITIVE MANUFACTURED LIGHTWEIGHT ALLOYS Christoph

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