The European Space Agency is currently examining various composite systems for the fabrication of large composite structures like the liquid hydrogen tanks for Re-usable Launch Vehicles (RLVs). In this body of work, the suitability of carbon fibre/PEEK, a high performance thermoplastic composite, was examined for space applications. A new form of carbon fibre/PEEK pre-impregnated tape is now industrially available with mechanical properties expected to equal or surpass those of existing suppliers. The main aim of this project was to thermomechanically characterise the new form of carbon fibre/PEEK for space applications under pressure formed autoclaved conditions, and to compare against properties achieved using the most suitable out of autoclave technology for large space structures. Thermoplastic in-situ automated tape placement (ATP) was chosen as the out of autoclave technique having most potential for the fabrication of large composite structures. Comprehensive mechanical testing was carried out on the carbon fibre/PEEK materials processed in order to compare the ATP mechanical properties versus the baseline autoclave properties. Laminates were manufactured using both manufacturing techniques to encompass the lay-ups that are commonly used in the aerospace industry; 0°, 0°/90°, ±45°, and quasi-isotropic configurations. Tests carried out on the materials included; tensile, compression, flexure, in-plane-shear and interlaminar shear. In order to simulate the temperature differentials present in a space environment, tests were carried out at incremental temperatures over the range of -70°C to 250°C. To simulate the affect of impact from space debris, compression after impact tests were carried out on the material. G IC and GIIC tests were carried out in order to characterise the fracture toughness of the carbon fibre/PEEK. Moisture uptake, which can contaminate and degrade space structures when in the presence of space vacuum was also analysed for both materials. Qualitative tests which were carried out following material processing included fibre volume fraction and DSC analysis. Ultimately, there may be a need to bond large composite sections together for RLV tanks. PEEK is an excellent hot melt adhesive and various bonding procedures have been developed to take advantage of this. Two of these are; resistance welding using metal mesh and amorphous interlayer bonding using PEI film. Laminates were bonded using both procedures and parameters were varied in an effort to establish the optimum method of bonding for the material. Following a trade-off study between the techniques, the bonding procedure of most promise was down-selected and full scale temperature testing followed.
|Number of pages||12|
|Publication status||Published - May 2008|