Graphite composites fabricated from thermoplastic polyetheretherketone (PEEK) IM7 graphite prepreg tapes were evaluated for the development of lightweight, strength-critical, dimensional stable spacecraft components. The objective of this investigation was to summarize the mechanical and physical properties of IM7 graphite/PEEK to compare its properties to that of similar graphite/epoxy composites.
A property database for thermoplastic composite materials was generated. Composite mechanical property characterization included 0° and 90° tensile and compressive, in-plane shear, and flexural properties. Physical property characterization included coefficient of thermal expansion, outgassing/condensable volatiles, and equilibrium moisture absorption at 71°C (160°F) and 95% relative humidity. Scanning electron microscopy (SEM) was used to investigate fiber/matrix distribution, fiber orientation, and fiber/resin interface adhesion. Results were compared with data on IM7 graphite/8551-7 epoxy laminates to assess the relative merits of the IM7 graphite/PEEK thermoplastic material system.
In general, IM7 graphite/PEEK thermoplastic composites possess a combination of properties that appear to match the requirements for several spacecraft applications. In addition to having very respectable structural properties, IM7/PEEK laminates exhibited lower moisture uptake and lower outgassing than IM7/8551-7 epoxy laminates. The equilibrium moisture gain for the thermoplastic composites was 0 18% compared to 0 80% for the epoxy composite system. SEM analysis indicated that the thermoplastic PEEK composite laminates exhibited excellent fiber/matrix distribution and interfacial fiber/resin adhesion. The PEEK thermoplastic matrix composite, therefore, provides a superior replacement to conventional epoxy matrix composites for spacecraft applications.