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The viscoelastic properties of polyphenylene sulfide resin based carbon fiber-reinforced composites have been examined using torsion, centrosymmetric disk (CSD), and three-point and four-point flexure testing modes. Laminates fabricated with carbon fabric and a quasi-isotropic layup of continuous carbon fiber have been considered. Dynamic mechanical tests have shown that these materials exhibit a glass transition interval (Tg) from 50 to 150°C and a melting transition near 280°C. The storage component of the modulus or stiffness decreases from room temperature to 175°C by an amount which varies with the imposed stress or strain state. Fiber-dominated modes (three-point and four-point flexure) exhibit a smaller percentage loss in modulus or stiffness than resin-dominated modes (torsion and CSD). Arrhenius plots obtained from frequency sweep data in the glass transition region indicate the fabric-reinforced material and quasi-isotropic layup have activation energies of 130 and 105 kcal, respectively, independent of testing mode. Superposition of frequency/temperature or time/temperature data was achieved in dynamic mechanical and transient (that is, creep and relaxation) tests, respectively. Projection of the ten-year modulus, stiffness, or compliance from transient tests suggests that the response is stress-state dependent with greater change observed for resin-dominated testing modes.
carbon fiber composites, thermoplastic composites, composites, viscoelasticity, creep, relaxation, dynamic mechanical testing, time-dependent properties, time-temperature superposition, frequency dependence, glass transition temperature
Senior staff engineer, Armco Research Center, Middletown, OH