Stave production
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.
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.
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
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
Isothermal DSC - prepreg For our case less information than temperature scan.
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
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.
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).
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 20+20 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.
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
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 25-60C 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.
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)