1. Stave production

2. Where we are Have built several full- and half-sized planks
We are not yet entirely happy with
Flatness:
Want to make new jigs, preferably in CF
Material:
Want to reduce amount of glue used
Extreme push: nearly glue-less stave
Core:
Corrugated core looks promising
Cure temperature
Would like to go to lower T. Will investigate different cyanate esters and might want to look into epoxy as well.
Recent co-cures have failed: this is not yet understood.
Co-cure failures have caused us to think again about material quality.

3. What we have learned recently
How do we quantify
Quality of material
Level of cure
This will help us controlling the quality of our material, and will help us in developing the optimum cure parameters (T, t, post cure cycles, etc.)
The methods to be used are
Differential Scanning Calorimetry (DSC)
Fourier Transform Infrared (FTIR) spectroscopy
The hardware for these measurements exists at RAL (Advanced material group, Simon Canfer and Steve Robertson). We had a very interesting conversation with Steve before Christmas and he did first measurements for us. We will continue along these lines.

4. Differential Scanning Calorimetry
A small sample (few mm3) is heated together with a reference sample, ΔT gives measure of heat capacity.
Can measure glass transitions, cure processes, etc.
2 modes:
Temperature scan
Isothermal
Heat –flux DSC
Power-compensation DSC

5. Temperature scan DSC - prepreg
Cure
Area under cure peak gives enthalpy set free during cure. If material has gone off this enthalpy will be smaller.
New: Prepreg which was stored in freezer (but from the oldest batch)
Old: Prepreg, which was left outside for several weeks after circuit breaker failure
Enthalpy reduced by 20%
Will measure best material we still have for comparison

6. Isothermal DSC - prepreg
For our case less information than temperature scan.

7. Temperature scan DSC – cured laminate
First heating shows still enthalpy from cure → Resin was only 85% cured (probably still acceptable)
Second heating shows glass transition at ~ 230°C

8. Fourier Transform Infrared spectroscopy
Measure the infrared absorption spectrum
This has peaks corresponding to the chemical bonds in the sample.
The IR spectrum is a fingerprint for a specific substance
For us interesting is the relative height of peaks belonging to the uncured and the cured CE.

9. FTIR – our samples appear dissappears
Steve reckons that the peak caused by the C≡N bond is disappearing, while the new peaks are due to the formation of the triazine ring.
The different height of the spectra is caused by the sample thickness.
This also looks promising, but more work is needed (sample preparation).

10. New material
Joining LBNL in an order for K13C2U/EX1515 (cure temperature 120°) from Tencate.
This will be for 100gsm and ~50gsm fibre density.
Material for approximately staves.
Found a UK supplier (Advanced Composites Group), which would do K13C2U (or comparable) with LTM123, which is a low-temperature CE resin (initial cure at 80°C) used in space science.
We do have a quote from them (fibre density 80gsm, which they believe is the lower limit of what they can do reasonably).
We will visit these guys in the next few weeks.

11. CF jig Complete & test carbon fibre based stavelet jig
Assembly ~ 50% done. Should complete by end Jan
Assembly trials & Evaluation (end Feb)
Develop full stave version (2 steps??) (end June)
Step 1: just a full sized version of stavelet jig (April)
Step 2: Incorporate ‘Oxford’ tooling. (June)
Full stave assembly trials & Evaluation (end Sep)
Final version of jig by Dec ‘11

12. Face-sheets Liverpool: Oxford:
Complete co-curing studies using 600mm curved carbon-fibre mould (end Jan)
Progress limited by ‘tape’ supplies
Low-Medium Temperature Lamination (end Feb)
Evaluate properties of tapes laminated to face sheets using Hysol 9396 cured for 25-60C and vacuum + 5 bar
2-ply Face sheets (end Feb)
Manufacture and assess 2-ply (asymmetric) face sheets for stavelet manufacture
Oxford:
Understand recent difficulties with co-curing
Use different jig orientations (concave vs convex)
Reduce material in jig, better temperature monitoring of material.
Progress limited by CF supplies.

13. Liverpool Stave(let) programme
Dummy stavelet (conventional 3-ply face sheets and honeycomb core) to check new jig (end Feb).
Electrical stavelet with co-cured/laminated bus tapes on 3-ply face sheets, Pocofoam blocks and 1/8” s/steel tube using new jig (end Mar).
Dummy stavelet (honeycomb core and ‘C’-channels) using 2-ply skins (end Mar)
Low mass stavelet with co-cured/laminated bus tapes on 2-ply skins with Allcomp foam and a 2.2mm OD titanium tube (end Apr?)
Dummy stave (conventional 3-ply face sheets and honeycomb core to check new jig (end Aug)
TM Stave (2 / 3-ply face sheets with co-cured / laminated bus tapes with Allcomp foam and a 2.2mm OD titanium tube) (end Sep)