The prototyping process was carried out for the Iso-Graphite stave with and without the di- amond powder in the carbon fibre pipe. The final drawing of the Iso-Graphite stave for the development of the prototype are shown in Figure 91.
FIGURE91: Generated associative drafting from 3D mechanical parts of the Iso- Graphite Vertical Split stave designed in Catia V5 (All dimensions are in mm)
In order to build the stave prototype, the tools were developed for producing the pipes, omega and for the stave final milling and assembly. The stave production process (Figure 92) began with the milling of the Iso-Graphite bulk which were supplied by Schunk Kohlenstofftechnik GmbH and three separate parts of the graphite were milled each upto a length of 250 mm. In order to produce the carbon fibre pipe, standard modulus T300 carbon fibre braid (orientation of ±45) were supplied by Barthels-Feldoff® GmbH. The braiding process was carried out with a teflon (Polytetrafluoroethylene PTFE) pipe with a diameter of 2.4 mm which resulted with a wall thickness of 0.3 mm. Vacuum assisted resin infusion without the diamond powder was performed (at the Institute of Composite Materials (IVW), Kaiserslautern). The braid was then cured in an autoclave at a static pressure of 24 bar close to 9 hours. An Omega was produced (at IVW, Kaiserslautern) with the prepreg carbon fibre with a lay up of [0/90/0] and was also cured in an autoclave. The stave parts (milled Iso-Graphite, the Pipe and an Omega) were then glued together with the epoxy-diamond powder glue. Upon curing, the stave final milling process was carried out with the aluminium vacuum tool where the excess remaining of the Iso-Graphite was milled in order to have a thickness of 0.5 mm (Figure 92). Finally, the fittings were connected to both the ends of the pipes in order perform the thermal measurements.
The second prototype of the Iso-Graphite stave was developed with diamond powder filled carbon fibre pipe. The diamond powder equivalent to a content of 13 % by volume fraction within the matrix (≈ 6 % by volume fraction within the composite) was mixed in to the epoxy resin.
Iso-Graphite Stave 105
FIGURE92: Iso-Graphite Vertical Split stave prototype production process
Vacuum assisted resin infusion technique (Figure 93) was then carried out, after which the carbon fibre pipe laminate was cured in an autoclave (at same pressure as explained before). After the curing process, the excess epoxy-diamond powder resin was scrapped off and the teflon pipe within the braid was also pulled out. The stave was then assembled and milled (Figure 93).
FIGURE 93: Production process and the assembly of the Iso-Graphite stave pro- totype with diamond powder filled carbon fibre pipe
Iso-Graphite Stave 106 Researchers at Nikhef (The National Institute for Subatomic Physics, Amsterdam) have re- ported that the epoxy resin does not function well with the liquid CO2. This is related to a problem of chemical compability. The researchers have also observed the problem of matrix cracking in the carbon fibre pipe while testing for pressure and leak rate with liquid CO2 inside the pipe. Even though further experiments were not performed and this problem is not fully understood, in order to overcome the problem of the matrix cracking and the high viscosity of the epoxy resin (filled with DP), another pipe was developed with the cyanate ester resin filled the diamond powder (Figure 94).
When compared to the epoxy resin, the cyanate ester resin has several advantages like,
1. high Glass Transition Temperature (Tg), easy pre-cure at moderate temperature (125 − 135◦C)¶¶.
2. a low viscosity at the room temperature before curing [86]. 3. low moisture absorption, high thermal stability [87].
4. radiation resistant [87], tough/resistant to microcracking caused by thermal cycling [87]. The standard modulus T300 braid was used and the same content (13 % by volume fraction within the matrix) of the diamond powder was mixed in the cyanate ester resin (after it was pre-cured) and the vacuum assisted resin infusion was performed after which it was cured in an autoclave.
FIGURE 94: Development of the carbon fibre pipe filled with diamond powder- cyanate ester resin
The pipes (CF-epoxy, CF-epoxy filled with DP, CF-cyanate ester filled with DP) were tested for the pressure tightness at 150 bar. This test was performed to qualify the pipe against the effect of the pressure and test was successful as all the pipes were able to withstand the pressure of 150 bar. The second test was conducted to measure the leak tightness of the pipe with the helium and the pipes showed a leak rate < 1E−7 atm cm3s−1
Stiffener Stave 107 5.6.2 Stiffener Stave
Development of the tools for the prototype
The designs for producing the aluminium tools for the stiffener stave prototype were developed as shown in Figure 95. The carbon fibre braid would be placed in the bottom tool after which the high modulus carbon fibres would be placed between the pipe and the same process would be carried out on the other side after the the tool would be sealed to undergo vacuum assisted resin infusion (with the diamond powder filled resin) along with the curing in an autoclave. The fittings (Figure 96) for the stave prototype was developed with CF-PEEK material which would be like an end block through the flow of the liquid CO2inside the pipe could be controlled.
FIGURE 95: Development of the design for an aluminium tool for the vacuum assisted resin infusion
FIGURE 96: Development of the design for the fittings for the prototype with CF-PEEK material
Development of the Double Iso-Graphite Stave for the Innermost Detector Layers 108
6
Development of the Double Iso-Graphite Stave
Changes in the specification 109