Tube to Foam Interface
(Tim)
Outline
• Discuss what’s known about the tube to foam
interface
– Describe problem
– Issues
– Theoretical Calculations
– Anecdotal Experience
30/05/2012
Tube to Foam Interface
2
Problem
•
Heat Flow
–
–
•
The heat generated within the active components on a stave is removed through evaporating CO2 in smallbore tubes.
The heat is conducted from the facesheets to the tube via thermally-conducting carbon foam and two
interfaces made using thermally-conducting adhesive.
Geometry
–
Tubes (S/steel so far)
•
–
For the future
•
–
2.2mm OD x 0.14mm wall (ABCN130)
Thermally-conducting Foam
•
•
•
1/8” (3.175mm) OD x (0.50, 0.25, 0.22mm wall)
Strip-staves:
Pixels:
Two 10mm wide ‘bars’
Full width ‘slabs’
Materials
–
Tubes
•
•
–
Thermally-conducting foam
•
•
–
Pocofoam
Allcomp foam
Tube-to-foam adhesives
•
•
30/05/2012
316L / 304L stainless steel (current staves & stavelets)
CP2 titanium (only used in UK ‘nearly glue-less’ stavelet
CGL (compliant)
Hysol EA9396 (30% BN by wt) (rigid)
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3
Issues / Concerns
• Thermal Performance
– Is the thermal impedance of the tube-foam interface
good enough to mitigate against thermal runaway
• Stave Mechanical Stability
– Are the temperature-induced stave deformations (and
associated stresses) small enough (stable enough) to
ensure good tracking performance.
• Longevity
– Will the thermal impedance of the joint deteriorate
over time?
– Could stresses induce creep
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Comparison
Rigid Adhesive
Compliant Adhesive
• Could the adhesive ‘slump’?
i.e. separate out under
– Gravity
– Capillary flow
• Could the adhesive ‘migrate’
away from the interface?
– Closed Cell foams
– Open Cell foams
• Could the adhesive become
less compliant?
– Irradiation induced ‘curing’
may produce a ‘rigid’ joint over
time.
30/05/2012
• Could thermally-induced
stresses lead to:– Large dimensional changes
– High stresses which might
promote cracking & ultimate
failure of thermal path
• Could the need to
accommodate dimensional
changes complicate stave
mounting?
– Fixations in Z
– Mounting brackets
• What are the effects of longterm creep?
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5
Open and Closed-cell Foams
• Allcomp Foam
– Open structure from
low density (0.05g/cc)
open cell foam
– 100-130ppi (0.25mm)
• Pocofoam
– Closed cell structure
with voids typically
0.5mm diameter
– Voids volume
equivalent to 0.22mm
thick glue layer
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Thermal Properties
Approximate Power Headroom Factor wrt 0.65mW/mm 2(0C)
1
2
4
6
8
10
12
Sensor Glue =>
IRS2125, 0.44W/m K
ALL Ks halved
Fluid htc (=>4000)
Foam Glue (BN/Hysol)
CFRP Kx
Cable Bus Ky
CFRP Ky
Foam Kxyz
Baseline
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16
Coolant Temperature Headroom wrt -30C [C]
17
18
19
20
21
22
23
24
• Second largest impact (after fluid htc)
• Doubling the thermal impedance of the foam glue reduces
the coolant temperature
headroom by 2⁰C (≈ 10%)
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Stave CTE Assuming Rigid Foam & Rigid Glue
• Simple 1D model (Classical Laminate Theory)
– 2 Face sheets (all 0/90/0)
• K13D2U / RS-3
• K13C2U / EX-1515
• K13C2U / EX-1515
[80gsm/29%RC]
[100gsm/40%RC]
[45gsm/40%RC]
– 2 Cooling tubes
• S/Steel:
• Titanium:
3.185mm OD x 0.22mm wall (x2)
Effective thickness 0.037mm
2.2mm OD x 0.14mm wall (x2)
Effective thickness 0.017mm
– 2 Bus Tapes
• 0.025mm Kapton cover-layer
• 0.025mm / 0.05mm Aluminium screen
• 0.100mm Kapton
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30/05/2012
-1.5E-06
Bare
Facesheets
Facesheets
+
S/S Tube
Facesheets
+
Ti Tube
Facesheets
+
Tape (50)
Tube to Foam Interface
Facesheets
+
Tape (25)
Facesheets
+
Tape(50)
+
S/S Tube
Facesheets
+
Tape(50)
+
Ti Tube
Facesheets
+
Tape(25)
+
S/S Tube
K13C2U[45gsm/40%RC][]s(0.025)+Ti
K13C2U[100gsm/40%RC][]s(0.025)+Ti
K13D2U[80gsm/29%RC][]s(0.025)+Ti
K13C2U[45gsm/40%RC][]s(0.025)+SS
K13C2U[100gsm/40%RC][]s(0.025)+SS
K13D2U[80gsm/29%RC][]s(0.025)+SS
K13C2U[45gsm/40%RC][]s(0.05)+Ti
K13C2U[100gsm/40%RC][]s(0.05)+Ti
K13D2U[80gsm/29%RC][]s(0.05)+Ti
K13C2U[45gsm/40%RC][]s(0.05)+SS
K13C2U[100gsm/40%RC][s](0.05)+SS
K13D2U[80gsm/29%RC][]s(0.05)+SS
K13C2U[45gsm/40%RC][]s(0.025)
K13C2U[100gsm/40%RC][]s with…
K13D2U[80gsm/29%RC][]s with…
K13C2U[45gsm/40%RC][tape/0/90/0]s
K13C2U[100gsm/40%RC][tape/0/90/0]s
K13D2U[80gsm/29%RC][tape/0/90/0]s
K13C2U[45gsm/40%RC]0/90/0/Ti/0/90…
K13C2U[100gsm/40%RC]0/90/0/Ti/0/9…
K13D2U[80gsm/29%RC]0/90/0/Ti/0/90…
K13C2U[45gsm/40%RC]0/90/0/SS/0/9…
K13C2U[100gsm/40%RC]0/90/0/SS/0/…
K13D2U[80gsm/29%RC]0/90/0/SS/0/9…
K13C2U[45gsm/40%RC]0/90/0
K13C2U[100gsm/40%RC]0/90/0
K13D2U[80gsm/29%RC]0/90/0
Stave 1D Model CTE
Stave CTE Assuming Rigid Foam & Rigid Glue
3.0E-06
2.5E-06
2.0E-06
1.5E-06
1.0E-06
5.0E-07
0.0E+00
-5.0E-07
-1.0E-06
Facesheets
+
Tape(25)
9+
Ti Tube
Historical Data
• Jones (2009)
– Crude measurement of relative CTE of CLG & Rigid
epoxy
– Measurement of thermal performance vs Thermal
cycling (15 cycles)
• Sutcliffe (2010)
– Stavelet FEA
• LBNL (2010)
– Thermal Cycling of 12cm rigid-glued prototypes
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– CGL
– ER2074 (rigid epoxy)
• Zero thickness glue line
• 0.1mm glue line
ER2074(0.0)
ER2074(0.0)
ER2074(0.1)
CGL
% strain
0.0233
0.0242
0.0187
0.0091
CTE (ppm)
4.57
4.75
3.67
1.78
40
0.035
30
0.03
20
0.025
10
0.02
0
0.015
-10
0.01
-20
0.005
-30
0
ER2074 '0'
-0.005
Stave Temperature
-40
-0.01
-50
0
60
120
180
240
300
360
420
360
420
480
540
600
Time (s)
0.04
ER2074
(0.0mm)
ER2074
(0.0mm)
ER2074
(0.1mm)
0.035
0.03
Thermal Strain(%)
• Cool down to -40C and
allow to rise back to
room temperature
0.04
0.025
0.02
0.015
0.01
0.005
0
-0.005
-0.01
0
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60
Tube to Foam Interface
120
180
240
300
Time (s)
480
540
600
11
Temperature (deg C)
• Clip-type extensometer
• 30cm prototypes
Thermal Strain (%)
Jones2009
Jones2009
• 30cm single-tube prototypes
– Equivalent thermal performance for CGL and rigid
epoxy
– Thermal cycling shows no deterioration of average
temperature above cooling tube at -40⁰C
30
Temperature (deg C)
20
10
0
-10
-20
-30
-40
-50
0
1
2
3
4
5
6
Time (h)
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Sutcliffe (2010)
• Standard UK build
– 0/90/0 K13D2U/RS3
(80gsm,29%RC)
– 1/8” s/steel tubes
• CTEs
– No Al screen
• 0.02mm contraction
• CTE = 1e-6
– 0.05mm Al screen
• 0.042mm contraction
• CTE = 2e-6
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Critical Stresses
• Foam stress (likely) to cause failure – but
structures survive!
• Two explanations
– Glue bridging between facesheet and tube
– Simple FEA assumes linear material
properties but materials testing reveals
otherwise
• UK Stave core design employs end closeouts to protect foam
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Mechanical Materials Measurements
• Pocofoam has
different properties in
orthogonal directions
and a failure stress of
typically 0.8MPa
3.5
3
1
Tensile loading of foam
2
Unloading of foam
Stress (MPa)
2.5
2
1.5
1
0.5
Failure
• Allcomp (K9) – 130ppi
has uniform
characteristics and
failure stress >2.5MPa
1 2
0
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Strain
Tube to Foam Interface
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LBNL (2010)
•
Construction
– Length 12cm
– Hysol 9396/BN(30% by weight) to bond tube & facings to
foam
– K7 foam
– One SS tube(2.8mm OD)
– One Ti tube(2.2 mm OD)
•
Thermal cycle and irradiation(time sequence)
–
–
–
–
•
900 cycles (20C<->-35C) then
1 cycle to -70C then
1 cycle to about -175C with LN2 then
Irradiation to 50 MRad, then to 150 Mrad total
No change in Thermal performance
– No difference in SS and Ti tubes (with given ID/OD). Not
a surprise (from FEA).
– No significant change in thermal performance for any
sample after any thermal cycle sequence, including LN2
– Effect of irradiation up to 1 GRad is <10% increase in T.
– Thermal performance with K9 foam is significantly
better than with K7 foam, by about 25%
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LBNL/BNL (2012)
Stave 1.3m x 0.12cm
Stave 1.2m x 0.12m
0/90/0 250 um thick K13D2U facings,
80-100 gsm pre-preg
Co-cured facings, low density 45 gsm
cf pre-preg. 0/90/0 370 um thick
K13C2U + bus facings
CGL around s/steel pipe, Allcomp foam
CGL around steel pipe, Allcomp foam
area[cm^2]
1560
Co-cure Stave Component Weights
Weight [grams]
Pipe
Foam
CGL
Facings
CF Tubes
Closeouts
Hysol
Honeycomb
Weight [g]
106.3
45.6
15
104.8
38.7
4.2
30.7
24.7
Total
370
fitings
16.6
new total
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facing 1
facing 3
two cf tubes
Stainless Steel Pipe+Fittings
closeouts
CGL on foam and pipe
foam
honeycomb
hysol 30% BN facing #1
hysol 30% BN facing #3
84.7
84.6
18.3
76.1
3.4
15.3
50.4
25.3
15.6
16.8
Total Stave Weight
390.4
386.6
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Comparison of Stave Stiffness, Room Temp and Chilled
Stave stiffness independent of temperature
(simple support 120 cm apart)
30/05/2012
Stave is about 10% stiffer when chilled with -30 deg-C
coolant. Bus cable glue layers responsible???
(simple support 120 cm apart)
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Co-cure stave contraction
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1.3 m stave and 1.2 m co-cure stave contraction
• Stave Contractions
– 1.2m co-cure stave contracts 0.2mm
• CLT predicts 0.118mm assuming completely free tube
• NB Stave is held together with 2 x 15g of Hysol – equivalent to 0.082mm thickness
spread over stave area
– 1.3 m stave expands ~ 20-35 um
• CLT predicts 0.040mm assuming completely free tube
• Similar glue mass / thickness
• Tube Length Changes
– Pipe moves into co-cure stave ~ 100 um, into 1.3 m stave ~ 160 um
– Free stainless steel pipe should contract ~ 1mm when cooled ~ 50 deg-C
– Question is: does pipe really contract 1 mm? If so, see analysis of 1.3 m stave
on next slide
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1.3 m stave contraction analysis
But we expected pipe
to be mostly fixed at
U-bend
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Summary & Conclusions
•
Stresses in staves come from
– Bus tapes (primarily the aluminium screen)
– Core assembly adhesive
– Cooling tubes (if assembled with rigid epoxy)
•
Evolving stave design reduces potential stresses
– Smaller bore tubes (ABCN130)
– Titanium (Progress in joining technology)
– Bus-tape screen (0.05mm -> 0.025mm -> ‘0’ ?)
•
CGL
– Experience since 2008
•
Many staves built showing good thermo-mechanical performance
– Concerns about migration into foam structure addressed by lining channel with rigid epoxy
– Reliance on ‘sliding’ properties over long service life in high radiation environment
– Some evidence that tube is not completely ‘free’
•
Rigid Adhesive (Hysol9396/30%BN)
– Experience since 2009
– Thermal cycling (tens to many hundreds)
•
No failures for ‘nominal’ cycling (Room temp to -40C)
– FEA shows stresses in all components (in particular the foam) have large safety margins for
‘nominal’ excursions and indicate that structures will survive large (160C) excursions.
30/05/2012
Tube to Foam Interface
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