UK Stave Work

Contribution to Strip Staves Local Supports

presentation at AUW

LSWG Meeting - Strip Stave Local Supports 2

Scope• Co-curing (8 slides) - TJJ

– Classical Laminate Theory for co-cured face sheets• CLT Calculations• Manufacture & test of tokens & comparison with CLT calculations

– Surfaces of Co-cured Facesheets• Potted history (successes & failures)• Properties of co-cured stave surfaces

• Stave Assembly Tooling (3 slides) - TJJ– Tooling Design– Stavelet 6

• Glue film for honeycomb

• Locking Mechanisms (6 slides) - SY

• Plans for Sector Prototype (3 slides) – SY

• ABCN130 Stave FEA (3 slides) - GB09/11/2011

LSWG Meeting - Strip Stave Local Supports 3

Co-curing – initial trials• 7 electrical and 2 mechanical co-cures of full size tapes & 4 stavelet

size– Co-cured face sheets can be sucked onto vacuum jig, although residual

curvature difficult to control along edge.– In autoclave gluing edge of tape needs to be protected from glue creep with

tape. – Larger residual twist in electrical tapes (thicker aluminium)– Dimensional changes measured– Concerns over face sheet integrity– Concerns over surface ‘roughness’

Autoclave cures for full length stave

Press cures for full length stave

Autoclave cures for 0.5mm stavelet on CF Tooling

09/11/2011

LSWG Meeting - Strip Stave Local Supports 4

Ripples, Defects & De-laminations• Ripples in Plank 5 tapes seen after

few 10’s of thermal cycles– Issue with tape manufacture?

• Defects– Detailed investigations of used/unused

face sheets reveal large variety of surface ‘defects’

• De-laminations (within CF face sheet)– 125C/4h co-cured K13D2U/RS3 face

sheets (US tapes) – De-laminations after 1 hour at -45C– Focus on theoretical calculations / FEA

modelling of stresses in co-cured structures together with a prototyping plan for verification 09/11/2011

LSWG Meeting - Strip Stave Local Supports 5

Surface Defects• Likely that these are from the

process– CFRP face sheets are free from defects

• Process (based on US technique)– Abrade tape with Scotch-brite / ethanol– Bake out tape over night at 110C– Lay up 0/90 & compact for 30’– Add top 0 layer & compact for 30’– Remove tape from oven, allow to cool &

add to stack.– Add release ply, silicone rubber pad &

caul plate, compact for 1hr– Transfer to autoclave & cure at 120 deg C

for 3 hours; release autoclave pressure & allow autoclave to cool over night with vacuum pump on;

• Surface Profiles– Initial 2D measurements using needle-

probe• New sample better than plank 5 but

worse than plank 4 0 2.5 5 7.5 10 12.5 15 17.5-10.0

-7.5-5.0-2.50.02.55.07.5

10.0Plank 4Plank 5Co-cure #1

Position (mm)

Defle

ction

(mic

rons

)

09/11/2011

LSWG Meeting - Strip Stave Local Supports 6

Classical Laminate Theory Applied to Co-cured face sheet (120C cure)

• Model– Assume copper has little effect– Aluminium thickness = 0.05mm– Aluminium modulus = 69MPa

• Classical Laminate Theory– In general, the loads [N] and moments [M], expressed as column

vectors, acting on a laminate can be related to the strains () and mid-plane curvatures () through the matrix equation;

– [A],[B] and [D] are 3x3 matrices called the extensional, coupling and bending stiffness matrices respectively.

• Extensional matrix [A] relates the resultant in-plane forces to the in-plane strains

• Bending matrix [D] relates the resultant bending moments to the laminate curvatures.

• Coupling matrix [B] couples the resultant forces and moments to mid-plane strains and curvatures.

– Solving the matrix equations gives the strains () and mid-plane curvatures ()

– Curvature seen in non-zero kappa values

K13C2U/EX-1515(0 deg)

0.065mm

K13C2U/EX-1515(90 deg)0.065mm

K13C2U/EX-1515(0 deg)

0.065mm

Kapton0.05mm

Kapton0.05mm

Aluminium0.05mm

Kapton0.025mm

09/11/2011

LSWG Meeting - Strip Stave Local Supports 7

Experimental Measurements

• Plot of height vs x2(where x is the position along the length) will have a slope of /2.

– 0/90 K3.6 (5.8)– 0/90/0+tape K 9.2 (11.5)

• Measure strain on top and bottom surfaces of 0/90/0+tape laminate vs temperature and compare with prediction from CLT

0/90/00/90

0/90/0 + tape 90/0/90 + tape

0

0 0.001 0.002 0.003 0.004 0.0050

0.005

0.01

0.015

0.02

0.025

0.03

f(x) = − 1.77890529885669 x + 0.0106056935538004

f(x) = − 4.62335517315441 x + 0.0255515487368161

0/90/0 + tapeLinear (0/90/0 + tape)

x2 (m2)

Heig

ht (m

)

0 20 40 60 80 100 120 140-4000

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

6000 Exp - topExp - bot -tomExp - diffCLT - topCLT - bot -tomCLT- diff

Temperature (deg C)

Stra

in (m

icro

-str

ain)

09/11/2011

LSWG Meeting - Strip Stave Local Supports 8

Effect of Aluminium Yield Strength• Use CLT to predict stresses for a given

temperature change

• Apply external moments to keep laminate flat & simulate sandwich construction

• Calculate using EXCEL– Split matrix summations into

constant part and aluminium modulus dependent part

– For a given temperature change• Use CLT to calculate stresses in each layer

with suitable external moments applied to keep laminate flat

• Sum to give total stress in aluminium layer

• Use aluminium stress and Ramberg-Osgood formula to calculate aluminium modulus for next temperature change

-120 -100 -80 -60 -40 -20 00

20

40

60

80

100

120Yield strength = 25MPaYield Strength = 50MPaYield Strength = 75MPaYield Strength = 100MPa

Temperature Difference (deg C)

Alum

iniu

m S

tres

s (M

Pa)

-120 -100 -80 -60 -40 -20 070%75%80%85%90%95%

100%105%110%

Yield strength = 25MPaYield Strength = 50MPaYield Strength = 75MPaYield Strength = 100MPaMeasurement

Temperature Difference (deg C)

Smal

ler C

urva

ture

rela

tive

to

E=69

MPa

09/11/2011

LSWG Meeting - Strip Stave Local Supports 9

Stresses in CF Layers vs. Al yield Strength

-200 -150 -100 -50 0-400

-320

Ply 1&3 (x) Stress vs Temperature

25

50

75

100

150

200

300

No Tape

Max. StressTemperature (deg C)

Stre

ss (M

Pa)

-200 -150 -100 -50 0-400

-320

Ply 2(x) Stress vs Temperature

25

50

75

100

150

200

300

No Tape

Max. StressTemperature (deg C)

Stre

ss (M

Pa)

-200 -150 -100 -50 00

20

40

60

Ply 1,2,3(y) Stress vs Temperature

255075100150200300No TapeMax. Stress

Temperature (deg C)

Stre

ss (M

Pa)

Unless the aluminium yield strength is very high, co-cured face sheets should be robust against thermal cycling down to operating temperature with a reasonable safety margin.

09/11/2011

LSWG Meeting - Strip Stave Local Supports 10

Co-curing Conclusions• Historically we’ve had mixed experience

– De-laminations• Some co-cures show signs of de-lamination – but not all

– Surface Defects• Some co-cures have very smooth surfaces – others do not

• Likely cause (of both!) is the lamination process– Take on-board expertise in US (LBNL September meeting) in

particular;• Bake-out of bus tape• Compactification during lay-up

– 1st sample looks encouraging

09/11/2011

LSWG Meeting - Strip Stave Local Supports 11

Stave Assembly Tooling• Programme to develop low(er) mass, more

stable stave assembly tooling– Start with CF sandwich version of stavelet

tooling to prove manufacturing techniques• 1.5mm CF skins on 7mm Nomex honeycomb• Embedded vacuum channel• FR4 vacuum channel network• ~ 380 2mm dia. vacuum holes

– Global flatness measured on CMM• 60% within +/- 10mictons

– Surface roughness measured using needle probe• Ra ~ 1.5microns

0 25 50 75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 5000

25

50

75

100

125

150

+0.03mm09/11/2011

0 2.5 5 7.5 10 12.5 15 17.5-10

-7.5

-5

-2.5

0

2.5

5

7.5

10

Position (mm)

Disp

lace

men

t (m

icron

s)

LSWG Meeting - Strip Stave Local Supports 12

Stave Version• Combination of the 2nd

Liverpool stavelet jig and the requirements for the Oxford stave assembly tooling for individual components

• Parts in fabrication at Liverpool & Oxford

• Hope to complete by end of 2011

09/11/2011

LSWG Meeting - Strip Stave Local Supports 13

Stavelet 6• Conventional build +

– New tooling– 80C cure glue film for honeycomb (~ 60% area removed using pattern cutter)

09/11/2011

LSWG Meeting - Strip Stave Local Supports 1414

UK Locking Mechanism Update

The UK stave mounting design is based on the edge mounting and end insertion. Once inserted into position, the stave is fixed at the Z=0.0 position at two locations, and along the long edge at 5 locations. The fixing condition at the Z=0.0 is fully locked on one side and guided on the other, and those along the long edge are “locked” in a manner that when the mounting points are locked, the stave is pressed against a pre-determined datum faces that guarantees the azimuth and radial positions of the stave, but allows differential thermal movement between the stave and the cylinder in the Z-direction.

Previous locking mechanism

09/11/2011

LSWG Meeting - Strip Stave Local Supports 15

Motivation of new locking mechanism• The existing design works when stave tilting angle at 16 deg.

– Can not fit into the space envelope when the stave tilting angle at 10deg.

• Further improvement of the existing design from the following aspects:– Reduce the number of parts– Reduce the number of reference faces to avoid over constraint– Further improvement on end insertion – Fit into the space envelop at stave tilting angle of 10o.

Number of parts reduced from 6 to 3. Material volumes very similar.09/11/2011

LSWG Meeting - Strip Stave Local Supports 16

Locking and Reference Faces

Cam (retracted)

Over centre dimples

Guide Rail interface

Reference faces

Unlocked, typ gap 0.2

Locked, 0 gap

Reference faces

Reference faces

4

2

09/11/2011

End insertion and tooling conceptSlide in guide rails using features in mounting brackets to locate.

Rotate guide rails so that the rails + the mounting bracket corms a continuous channel. Secure by inserting rode (green)

Stave slides along channels via the locking points. When the stave is in the correct location, the stave is locked in Z, the cams are actuated and the guide rails removed.

Note: Guide rails are only used during insertion of the stave, and are fully withdrawn once insertion has finished.

LSWG Meeting - Strip Stave Local Supports 18

3D illustration09/11/2011

LSWG Meeting - Strip Stave Local Supports 19

Being supported at various rotational positions

09/11/2011

LSWG Meeting - Strip Stave Local Supports 20

Clearance within space envelope (for 10o stave tilt angle) including that for the rotation of the guide rails.

Space envelope

Innermost layer Geometry and Stave Envelope

09/11/2011

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Remarks• The new locking mechanism design fits into the revised space

envelope when the stave tilt angle is 10

• A prototype of the new locking mechanism has been made out of PEEK, and is working as expected.

• This new design allows end insertion to be carried out during installation as well as stave removal should this proves necessary after installation;

• Plan to build a stave sector prototype with 4 staves to demonstrate the end insertion and positioning of the locking mechanism. The design and construction of this setup is now underway and we aim to get this done by the early next year.

09/11/2011

LSWG Meeting - Strip Stave Local Supports 22

Stave Sector Prototype

Carbon Fibre sandwich sector base

some tooling balls will be fitted on various position on the sector for easy survey.

FEA carried out to check the interlink rigidity.

09/11/2011