Creep and physical aging in a polyamideimide carbon fiber composite

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Abstract
The creep properties of an amorphous thermoplastic polyamideimide and its continuous carbon fiber composite have been investigated. Creep behavior in the viscoelastic (low stress) and viscoplastic (high stress) ranges was examined. The interaction of physical aging with the creep behavior of the material was found to be significant in both stress regimens. Physical aging shifted creep curves to longer times in the viscoelastic range, reducing the total amount of creep strain in both the viscoelastic and viscoplastic ranges. The amount of nonrecoverable strain produced during viscoplastic creep was highly dependent upon the amount of time a sample was held under load due to concurrent physical aging. Specimens aged significantly prior to testing showed no undue time dependence in the amount of nonrecoverable creep strain produced. The viscoplastic creep behavior was shown to be composed of instantaneous localized plastic deformation, viscous strain, stiffening due to aging, and densification due to aging.