Beryllium window experiment at - PowerPoint Presentation

Slide1

Beryllium window experiment at HiRadMat

1Chris Densham, 1Tristan Davenne, 1Andrew Atherton, 1Otto Caretta, 1Peter Loveridge, 2Patrick Hurh, 2Brian Hartsell, 2Kavin Ammigan, 3Steve Roberts, 3Viacheslav Kuksenko, 1Michael Fitton, 1Joseph O’Dell, 2Robert Zwaska

1

STFC Rutherford Appleton Laboratory, UK

2

Fermilab

, US

3

Oxford University (Materials for Fission and Fusion Power), UK

Slide2

Objectives of experiment

Identify design limits for beam windows for the next generation of proton accelerator driven facilities by:Exploring the onset of failure modes (flow behaviour, crack initiation, or fracture, and other degradation) of various beryllium grades/forms under controlled conditions at simultaneous high localized strain rates and temperature rises.Identifying and quantifying any potential thermal stress wave limits for beryllium windows under intense pulsed beam conditions and how they may differ between grades/forms  Comparing measurements to non-linear failure simulations for validation/modification of material models through the use of state-of-the art material analysis techniquesInvestigating the potential effects of resonance, with constructive superposition of stress waves, in windows of particular thicknesses/geometries.

Slide3

Model Inputs

Fluka and MARS Energy Deposition calcsMax energy density = 0.2 GeV/cc/primary Temperature jump = 1.7K/bunch or 493K/spill HiRadMat Proton Beam ParametersBeam kinetic energy - 440GeVBeam Sigma – 0.3 - 0.5mmBunch spacing - 25nsNumber of protons/bunch = 1.7e11Number of bunches – 288Spill duration - 7.2μsStress simulations (Static and inertial)LS-Dyna, Autodyn and ANSYS Beryllium window – temperature dependent strength propertiesBilinear and elastic-viscoplastic hardening models Window dimensions: Radius range = 5-25 mm Thickness range = 0.15-1 mm (0.15mm chosen such that bunch spacing=2*t/cL)

Model inputs

Slide4

Beryllium Material Data

[ITER MATERIAL PROPERTIES HANDBOOK 1997] [Mechanical Properties of Structural Grades of Beryllium at High Strain Rates, US Air Force Materials Laboratory, 1975]Stress Strain curves for Beryllium S-65BYield Strength of Beryllium S-65BCombined ITER and US Air Force data used to implement Bilinear Kinematic Hardening material model in ANSYS ClassicLiterature data on mechanical properties of beryllium at high strain rates

Approximated using elastic viscoplastic model in LS-Dyna simulations

Slide5

Beryllium Material Data

Tangential Modulus = 4.62 GPaBi-linear kinematic model used in ANSYS

Slide6

Beam Induced Stress

Bi-linear ModelStatic structural analysis of thermal stresses induced by beam pulse Temperature dependent material propertiesWindow properties:25mm radius, 1mm thicknessTemperature jump of 360°C Bi-linear

Von Mises Stress [MPa]

268

Total Strain

1%

Axial Dispacement [

μ

m]

5.71

Beam induced stress & strain

Slide7

Edge strain simulation results

Be slugs: R = 20 mm, L = 30 mmBeam centered at r/R = 0.9 Beam sigma: 0.3 mmElastic viscoplastic material model (LS-DYNA)Temperature and strain rate dependent [1]LS-DYNA model showing beam location and temperature after 288 bunches.Dynamic simulations

Slide8

Dynamic strain response

E: elastic material modelEVP: elastic viscoplastic model288 bunches36 bunchesΔT = 120 °CMax. εtot,equiv = 0.08 %

ΔT = 980 °CMax. εtot,equiv = 2.0 %

Slide9

Plastic strain: generation of permanent surface displacement

y-displacements, σ = 0.3 mmy-displacements (bump height) range from 2 – 10 µm (σ = 0.3 mm, t = 0.25 – 3 mm) – well within resolution of modern profilometersDamage model being developed to better predict onset of fracture and fracture morphology after cool-down (fracture of centre spot expected)

Slide10

Results are for

0.25 mm window, elastic viscoplastic material modelAt maximum intensity:(288 bunches/pulse)Surface deformation versus beam sigma / intensity

Slide11

Beam and Applied Pressure

A pressure is applied to one side of window as is the case in an actual beam windowInvestigate whether addition of beam pulse could produce significant stress peakWindow is constrained at periphery edge.Investigated the influence of altering the window radius and thickness and magnitude of pressure load. Stress response of window under beam and pressure load of 4 barRealistic load case: beam pulse + applied pressure

Slide12

Interim conclusion

Applying a pressure to the window in conjunction with beam loading does not appear to induce a higher stress peak in the window (good result for actual beam windows!) Nevertheless, it may still be a valid method of detecting window failure e.g. by using an on-line leak detector Realistic load case: beam pulse + applied pressure

Slide13

Outline conceptual design of experiment

Multiple samples exploiting long interaction length in beryllium.Samples include:Different commercial grades of BeThick & thin windowsUnstressed and pre-stressed

Slide14

Online instrumentation

Strain measurements: strain gages positioned on surface of beryllium slugs to measureaxial straincircumferential strainLaser Doppler Vibrometer to compare surface vibrations with simulations and provide independent check on rms beam spot sizeOptical pyrometer to measure peak temperature rise (another check on beam size) HRMT14 experiment: Equipped Inermet specimen for strain measurements [2]

Slide15

Off-line materials analysis

Profilometer/AFM to analyse window surface profile and measure out-of-plane plastic deformations.Advanced microscopy systems for micro-structural and crystallography evaluation (SEM, EBSD, EDS) and potential crack/failure analysis.

Slide16

Proposed experimental methodology

Polish samples before irradiation and characterise using AFM, SEM, EBSD, EDS, nanoindentation and, possibly, micromechanical methodsCarry out experiments:Scan beam across samples with increasing number of bunches per spillCarry out multiple shots on single locations to investigate whether beam effects saturate or accumulateRepeat measurements in step 1 to identify effects of pulse beam interation

Slide17

Material analysis techniques

Used before and after in-beam experiment to quantify effects of pulsed beam interaction with material

Slide18

Atomic Force Microscopy

Used to measure surface bump dimensions

Slide19

Electron backscatter diffraction (EBSD)

Electron backscatter diffraction is a technique for the scanning electron microscope which allows crystal orientations in a polycrystalline material to be measured.Maps of crystal orientation can be collected using EBSD. They remove any ambiguity regarding the recognition of grains and grain boundaries in the sample.We intend to use EBSD to see how the material flows during plastic deformation and, if a crack develops, how the flow results in fracture

Slide20

Nanoindentation

Used to measure changes in hardness across sample after irradiation

Slide21

Focussed

Ion Beam (FIB) MethodsZeiss Nvision dual beam FIB-SEM SampleFIB technique advantageous for:Site specific regionsSmall volumes – reduction in hazards e.g. activity, toxicity, etc.

Slide22

Micromechanical Testing

Steve RobertsOxford University Materials

2

m

m

Slide23

23

Why microcantilevers?Need for a sample design that can be machined in surface of bulk samples.Bend testing allows fracture as well as elastic and plastic properties to be investigated.Suitable for measuring individual microstructural features.Testing of samples only available in small volumes.Geometry that can be manufactured quickly and reproducibly.

1u

m

3u

m

2u

m

3u

m

4u

m

Slide24

Neutron-irradiated

UnirradiatedIon-irradiated

Micromechanical testing Fe-6%Cr – yield stress

6

.0

4.0

2.0

0.0

0.0

2.0

4

.0

6.0

8.0

Yield Stress (

G

Pa)

Beam depth (

m

m)

0.1mm

Slide25

Energy-dispersive X-ray Spectroscopy (EDS)

Used to measure migration of impurities e.g. to grain boundaries

Slide26

Summary of measurements

1) Plastic deformation out-of-plane profile.2) Vibration (strain gauges) response (onset of yielding, fracture timing (in cool-down cycle?))3) Crack/fracture detection through microscopy4) Fracture surface morphology through microscopy (inter-granular?)5) Grain orientation and residual strain through microscopy (EBSD)6) Visual (High Speed or High Resolution Camera) to capture any unforeseen events

Slide27

Interpretations of measurements

Do measurements match the macro-scale simulations and/or material/damage models? (Validation, Benchmarking)Are results consistent across the various Be grades and conditions tested? Can materials characterisation explain any differences noted? Do results indicate that certain grades/conditions/orientations exhibit better resistance to thermal stress waves? Does resonance between bunches have a measureable effect?Can one primary failure mode be identified for all material grades/conditions or does the failure mode differ depending upon material/grade/condition? Was anything observed that was not expected?

Slide28

Extra Material

Slide29

Influence of Cp

Temp dependent CpConstant Cp 

Temp Dependent Cp

Constant

Cp

Temp [°C]

362.8

461

Von

Mises

Stress

[

MPa

]

268

273

Plastic Strain

0.009

0.014

Influence of

Cp

Slide30

Stress at window centre following a

single bunch. Note ‘small’ magnitude of stress waves and significant reduction in stress wave magnitude within several bunchesAxial stress at window centre during first six bunchesAxial wave magnitude increases for first three bunchesno significant constructive interference of axial waves observedInertial stresses from single pulse

Slide31

Inertial Stress – complete pulse

Stress resulting from entire pulse (288 bunches)Plastic deformation starts at about 2μsPeak stress is 260MPaInertial stress waves don’t appear to significantly add to stressAxial strain rate < 25000 s-1Radial strain < 900 s-1Strain rate reduces once plastic deformation occurs

Inertial stress from complete spill

Slide32

Inertial Stress – complete pulse

Plastic work occurs on beam axisAxial Deformation of 0.6microns with 0.15mm thick windowStrain growth rate changing at yield point

Inertial stress from complete spill