Summary,Conclusions and Recommendations 153 thermoplastic based composites,especially in the cases of thick and tapered laminates or during a repair process using welding techniques 8.3 Thermoplastic Composites In general,mechanical properties of thermoplastic composites are similar to those of thermoset composites.Thermoplastic composites also perform very well at elevated temperature but additional data concerning the retention of properties at elevated temperature and under combined hot/wet conditions are sorely needed,especlally the matrix dominated properties.Thermoplastic composites exhibit lower shear and compression strength than those of thermoset composites.Studies should be undertaken to better understand why they are weaker and how these properties can be improved.It seems that fibre/matrix adhesion and fibre distribution.fibre alignment and shear stability may be very important contributing factors to the compressive response. Relationships used to predict the composite properties of thermoset composites from their neat resin propertles may not be applicable to thermoplastic composites.Correlations enabling prediction of thermoplastic composite performance from the neat resin evaluation should be therefore investigated. One of the main advantages of using thermoplastic composites in aircraft structural applications over thermoset composites is their markedly superior damage resistance and tolerance.Thermoplastie composites exhlbit toughiness values up to ten umes higher than those of thermosets.The delamination behavior of thermoplastic composites as demonstrated by ICI's APC-2 (PEEK)composites is different to that of thermoset composites.APC-2 exhibits non-linear viscoelastic behavior which is rate dependent.Epoxy resin does not plastically deform to the same extent as PEEK resin. Thermoplastic composites seem to perform reasonably well in fatigue but their creep resistance is probably lower than thermoset composites.However,the few data on fatigue and creep propertles of current thermoplastic composites are insufficlent to conclude whether or not theroplastic comnposites offer any advanlages over epoxy based composiles. From the limited data available.the resistance of thermoplastic composites to thermal cycling and radiation encountered in LEO and GEO orbit appears to be comparable to that of thermoset composites.Further work is needed to assess the potential of thermoplastic composites for use in space structures.Summary, Conclusions and Recommendations 153 thermoplastic based composites, especially in the cases of thick and tapered laminates or during a repair process using welding techniques. 3.3 Thermoplastic Composites In general, mechanical properties of thermoplastic composites are similar to those of thermoset composites. Thermoplastic composites also perform very well at elevated temperature but additional data concerning the retention of properties at elevated temperature and under combined hot/wet conditions are sorely needed, especially the matrix dominated properties. Thermoplastic composites exhibit lower shear and compression strength than those of thermoset composites. Studies should be undertaken to better understand why they are weaker and how these properties can be improved. It seems that fibre/matrix adhesion and fibre distribution, fibre alignment and shear stability may be very important contributing factors to the compressive response. Relationships used to predict the composite properties of thermoset composites from their neat resin properties may not be applicable to thermoplastic composites. Correlations enabling prediction of thermoplastic composite performance from the neat resin evaluation should be therefore investigated. One of the main advantages of using thermoplastic composites in aircraft structural applications over thermoset composites is their markedly superior damage resistance and tolerance. Thermoplastic composites exhibit toughness values up to ten times higher than those of thermosets. The delamination behavior of thermoplastic composites as demonstrated by ICI’s APC-2 (PEEK) composites is different to that of thermoset composites. APC-2 exhibits non-linear viscoelastic behavior which is rate dependent. Epoxy resin does not plastically deform to the same extent as PEEK resin. Thermoplastic composites seem to perform reasonably well in fatigue but their creep resistance is probably lower than thermoset composites. However, the few data on fatigue and creep properties of current thermoplastic composites are insufficient to conclude whether or not thermoplastic composites offer any advantages over epoxy based composites. From the limited data available, the resistance of thermoplastic composites to thermal cycling and radiation encountered in LEO and GE0 orbit appears to be comparable to that of thermoset composites. Further work is needed to assess the potential of thermoplastic composites for use in space struCtures