1. A comparison of Some Properties of Sandwich Test Tokens with Various Core Materials
(Tim)

2. Properties of Sandwich Test Tokens
Aim
Previously have destructively measured (3-pt bend & FWT) sandwich test tokens (before & after irradiation)
K13D2U/RS-3 80 gsm/ 29%RC (0/90/0)
UCF-126-3/8-2.0 honeycomb
Hysol EA9396 / ACG VTA260 (film)
Different failure modes
Hysol: failure of glue interfaces at low load
VTA260: failure of facesheets but at much higher loads
This work
Begin to repeat previous tests with more samples, different materials, different glues / application techniques
Limit measurements to 3-pt bend as force-extension curve gives compliance, failure load and information on failure mechanisms.
28/08/2012
Properties of Sandwich Test Tokens

3. Properties of Sandwich Test Tokens
Previous Work
3-pt bending
All sample sealed in vac-bag material to contain debris
Measure load vs extension
Break at maximum load
Slope gives approximate bending compliance
Post maximum behaviour reveals failure mechanism
28/08/2012
Properties of Sandwich Test Tokens

4. Properties of Sandwich Test Tokens
Results
Sample
Slope
N/mm
50N
100N
150N
200N
300N
400N
Hysol / non-irrad
262
Pass
114.1
Hysol / irrad
269
79.4
VTA260 / non-irrad
396
297
VTA260 / irrad
379
322
28/08/2012
Properties of Sandwich Test Tokens

5. Properties of Sandwich Test Tokens
Failure Mechanisms
Peak followed by monotonic fall
Characteristic of single break in top facesheet under roller
Glue joints intact
Peak followed by ‘staircase’
Characteristic of progressive failure of glue joints
Face sheets & honeycomb intact
28/08/2012
Properties of Sandwich Test Tokens

6. Properties of Sandwich Test Tokens
New Samples
Geometry
150mm x 40mm (width determined by corrugations)
Common items
K13D2U/RS-3 (80gsm,29%RC) 0/90/0 (& 90/0/90)
Hysol EA9396 glue bath (0.5mm deep)
All samples cured in 2 steps at 66C
Core Materials
UCF-136-3/8-2.0 Carbon fibre honeycomb
Cell size ~ 9.6mm
Schutz Cormaster N636 (‘Korex replacement’)
Cell size ~ 4.8 mm
QMUL Corrugation
13mm pk-pk / 100gsm plain-weave (+/- 45deg)
Test
3-point bending
Increased maximum load
Eg: 100N, 150N, 200N...
Record failure load and slope at between 80 and 120N (if possible) else 60N to end of linear region
‘0’
28/08/2012
Properties of Sandwich Test Tokens

7. Properties of Sandwich Test Tokens
Corrugated CFRP Core?
Original Motivation: Ultracor CFRP honeycomb is expensive – what does it do for us?
Thermal Conductance across stave:
Sensor + Facing ~ 0.3mm × 200W/mK mm × 140 => 90.
Honeycomb: 2mm × 3W/mK => 6 … i.e. 7% improvement BUT problem coupling to it! Honeycomb is ignored in UK thermal FEA)
Alternative: 45o weave CFRP pre-preg: cured between precision plates machined to produce a corrugated CFRP.
28/08/2012
Properties of Sandwich Test Tokens

8. Plank #5 Corrugation with dot pattern of Hysol 9396
BN-loaded Hysol for POCOfoam
20/09/2011

9. Issues (potential) with Corrugations
Mechanical Structure very similar to cardboard box / packaging!
Stiff along length (tilted walls) and width (trapezoidal structure).
Relatively easy to fold width-wise (ultimately facing buckles / breaks).
Natural to consider combination with facings (i.e rotated wrt usual) - Lower facing Z modulus compensated by corrugations. Hence:
Improved X thermal conductance: Temperature Headroom 21.5 => 23.2 degrees (more so for DCDC etc?). More uniform T vs X.
Co-cured facing easier to assemble? (curl along length?)
Double up 90 layers: mechanically safer for (UK) cantilever mount?
Geometry & Mass Issues
(very) slight ripple in across X ?
slightly more massive (needs optimising).
28/08/2012
Properties of Sandwich Test Tokens

10. Properties of Sandwich Test Tokens
0/90/0 Beams
0/90/0 Beams
CF Mass
Core Mass
non-glue parts
Final
Mass
Glue Mass
Glue
/m2
% glue %
(core
+ glue)
Thk (mm)
Core (mm)
(hcf/h)^3
D (N/mm)
Failure (N) CF
3.949
1.052
5.001
5.318
0.316 33 6%
26%
5.45
5.08
1.00
268
100
N636
0.908
4.857
6.335
1.478
154
23%
38%
5.65
5.28
0.89
279
199
Corrug
1.205
5.154
5.856
0.703 73
12%
33%
4.88
4.51
1.43
247
122
N626#2
5.948
1.091
114
18%
34%
5.63
5.26
0.90
273
167
28/08/2012
Properties of Sandwich Test Tokens

11. Properties of Sandwich Test Tokens
90/0/90 Beams
90/0/90 Beams
CF Mass
Core Mass
non-glue components
Assembled Mass
Glue Mass
glue/m2
% glue
% (core+glue)
Thk (mm)
Core (mm)
(hcf/h)^3
D (N/mm)
Failure (N) CF
3.82
1.0250
4.8450
5.3403
0.4953 52 9%
28%
5.55
5.18
1.00
129 75
N636
0.9650
4.7850
5.9148
1.1298
118
19%
35%
5.68
5.31
0.93
234
150
Corrug
1.2850
5.1050
5.6953
0.5903 61
10%
33%
4.86
4.49
1.54
184 99
28/08/2012
Properties of Sandwich Test Tokens

12. Properties of Sandwich Test Tokens
Conclusions (so far)
CF Honeycomb beams
Slope ≈ 270N/mm
Failure load ≈ 100N
Very similar to 2011 beams
Failure is ALWAYS at glue interface between honeycomb and face sheet
Corrugated Beams
Slope ≈ 250N/mm so very similar to CF (and N636) beams DESPITE being 0.5mm thinner!
Failure at about 122N – buckling of facesheet in un-supported regions
N636 Beams
Highest mass (x2 range in glue gsm), failure loads ( N) & bending stiffness
0/90/0 vs 90/0/90 looks strage!
28/08/2012
Properties of Sandwich Test Tokens

13. A note on Honeycomb Glue Mass
28/08/2012
Properties of Sandwich Test Tokens

14. Transverse Bending Stiffness of 120mm beams
Samples
0/90/0 + corrugation (90)
0/90/0 + N636
90/0/90 + N636
Use 1.6mm aluminium shims to spread loads & prevent premature face sheet failure
Adjust bending length to 93mm to optimise for corrugation geometry
‘0’
28/08/2012
Properties of Sandwich Test Tokens

15. Transverse Bending Stiffness of 120mm beams (L ≈ 93mm)
Corrugation
N636
Transverse
Beams
CF Mass
Core Mass
non-glue parts
Assy
Mass
Glue Mass
Glue
/m2 %
glue
% (core
+glue)
Thk (mm)
Core (mm)
(hcf/h)^3 D
(N/mm)
Failure (N)
N636 (90/0/90)
3.056
0.772
3.828
4.57
0.742 77
16%
33%
5.68
5.31
0.93
161
182
N636 (0/90/0)
5.15
1.322
138
26%
41%
212
243
Corrug (Trans)
1.028
4.084
4.53
0.446 46
10%
4.86
4.49
1.54 37 40
28/08/2012
Properties of Sandwich Test Tokens

16. Properties of Sandwich Test Tokens
Improving the Longitudinal Bending Properties of Hysol-Glued Beams With CF Honeycomb
Hysol-glued beams with UCF-126-3/8-2.0 honeycomb fail at:-
80N, 114N (2011 non-irradiated samples)
75N, 100N (2012 samples)
Glue Application
Dip honeycomb in trough of depth ~ 0.5mm
Agitate a bit
Leave for a couple of minutes
Hysol-glued UCF honeycomb cores always have low mass & failure load
How much glue is needed to raise failure load?
Methods
Stencil
Uniform thin layer
28/08/2012
Properties of Sandwich Test Tokens

17. Properties of Sandwich Test Tokens
Stenciling
Laser-cut 0.5mm thick perspex stencil
Need to load adhesive with hollow micro-spheres to increase viscosity to inhibit bleed under stencil (and reduce density)
0/90/0
150 x 40mm
CF Mass
Core Mass
Non-glue Parts
As built Mass
Glue Mass
glue/m2
% glue
% (core+glue)
Thk (mm)
Core (mm)
(hcf/h)^3
D (N/mm)
Failure (N)
CF + Stencil
3.879
1.025
4.904
6.053
1.149 96
19%
36%
5.48
5.11
1.00
370
218
28/08/2012
Properties of Sandwich Test Tokens

18. Properties of Sandwich Test Tokens
Stencil Beams
Break at 218N due to failure of the (top) face sheet under top roller
28/08/2012
Properties of Sandwich Test Tokens

19. Properties of Sandwich Test Tokens
Uniform Glue Layer
Application
Spread thin(-ish) glue layer over whole face sheet
Locate honeycomb
Cure
0/90/0 150x40mm
CF Mass
Core Mass
Non-glue Parts
As built Mass
Glue Mass
glue/m2
% glue
% (core+glue)
Thk (mm)
Core (mm)
(hcf/h)^3
D (N/mm)
Failure (N)
Hysol film
3.879
1.025
4.904
6.01
1.106 92
18%
35%
5.48
5.11
1.00
284
153
28/08/2012
Properties of Sandwich Test Tokens

20. Properties of CF Honeycomb beams vs glue mass
Method
Sample
Date
Glue Mass
(g/m2)
Bending Stiffness (N/mm)
Failure Load
(N)
Dip
2011
N/A
262, 269
79,114
2012 33
268
100
Stencil 96
370
218
Even Layer 92
284
153
VTA260
188
379, 396
297,322
Notes
VTA260 mass can be reduced by cutting out honeycomb pattern
Loading Hysol with hollow glass spheres seems to stiffen the adhesive ?
28/08/2012
Properties of Sandwich Test Tokens

21. Properties of Sandwich Test Tokens
What Next?
Establish the ‘machine stiffness’ (don’t have a true displacement sensor) to enable the exact load-extension curves to be determined
Cantilever bending of transverse test samples
Short section with ‘full stave’ cross-section (i.e. C-channels, core, Pocofoam etc..
Clamp at one side using 15mm x 4mm block glued into C-channel & load ‘free’ end
Try Amber Composites EF8020 (100gsm) glue film
Repeat stencilling trials with different amounts of hollow glass spheres
Investigate if it’s possible to control the amount of glue N636 honeycombs ‘pick up’ during a simple ‘dip’
Investigate effects of cure temperature and pressure
28/08/2012
Properties of Sandwich Test Tokens