Summary,Conclusions and Recommendations 155 8.6 Aircraft Applications of Thermoplastic Composites The replacement of metallic and fibre reinforced thermoset components with thermoplastic based composites is now occurring.Even though applications of thermoplastic composites in primary and secondary aircraft structures are becoming increasingly common. they have not yet recelved wide acceptance.The inertia in utilizing them in aircraft structural applications is attributed mainly to the unanswered questions concerning their fatigue and creep behavior and poor compression properties,the lack of processing experience.the high cost and the limited data avallable.It is obvious from this review that more research on thermoplastic composites is needed.More data have to be generated,especially for other thermoplastics besides PEEK and PPS that deserve attention. Each thermoplastic matrix has its own advantages and disadvantages;the final selection depends malnly on the applicalion,parlcularly in terms of stress or strain involved, time under load,environmental conditions,solvents involved and costs.For higher temperature applications.such as supersonic aircraft.polyimides and polybenzimidazoles are promising choices,but there is a draw-back of difficult processing.If moisture resistance is required,polyamideimdes should be avoided.If exposure to aircraft fluids is likely to occur, then polysulfones should be elminated.For very high toughness requirements.all thermoplastic resins are suitable except polyphenylene sulfide which has Gre toughness values similar to the thermoset ones.Overall the polyketone family is a judicious choice as it offers well balanced properties.Except for their outstanding toughness,the mechanical properties of polyketones are not exceptional but they are at least comparable to conventional thermosets. They exhibit excellent solvent and moisture resistance and they have good melt processability. Amongst the thermoplastic polymers in the polyketone family.ICI's polyetheretherketone polymer(PEEK)has the advantage of an extensive database established by the manufacturers, the scientific community and aircraft designers and engineers.however the latest polyketones exhibit higher Tgs than the well known PEEK.Summary, Conclusions and Recommendations 155 6.6 Aircraft Applications of Thermoplastic Composites The replacement of metallic and fibre reinforced thermoset components with thermoplastic based composites is now occurring. Even though applications of thermoplastic composites in primary and secondary aircraft structures are becoming increasingly common, they have not yet received wide acceptance. The inertia in utilizing them in aircraft structural applications is attributed mainly to the unanswered questions concerning their fatigue and creep behavior and poor compression properties, the lack of processing experience. the high cost and the limited data available. It is obvious from this review that more research on thermoplastic composites is needed. More data have to be generated, especially for other thermoplastics besides PEEK and PP.3 that deserve attention. Each thermoplastic matrix has its own advantages and disadvantages: the final selection depends mainly on the application, particularly in terms of stress or strain involved, time under load, environmental conditions, solvents involved and costs. For higher temperature applications, such as supersonic aircraft, polyimides and polybenzimidazoles are promising choices, but there is a draw-back of difficult processing. If moisture resistance is required, polyamideimdes should be avoided. If exposure to aircraft fluids is likely to occur, then polysulfones should be elminated. For very high toughness requirements, all thermoplastic resins are suitable except polyphenylene sulfide which has GI, toughness values similar to the thermoset ones. Overall the polyketone family is a judicious choice as it offers well balanced properties. Except for their outstanding toughness, the mechanical properties of polyketones are not exceptional but they are at least comparable to conventional thermosets. They exhibit excellent solvent and moisture resistance and they have good melt processability. Amongst the thermoplastic polymers in the polyketone family, ICI’s polyetheretherketone polymer (PEEK) has the advantage of an extensive database established by the manufacturers, the scientific community and aircraft designers and engineers, however the latest polyketones exhibit higher Tgs than the well known PEEK