The characterization of physical aging in polymeric composites

The physical aging of an IM7/977-3 polymeric composite was studied by using creep compliance tests. Momentary creep tests were conducted at constant tensile loads within viscoelastic range and under isothermal condition, 104°C. Off-axis composite specimens with 90°, 45°, 30°, and 15° fiber directions were used to characterize the orthotropic creep compliance for different aging times. The effects of aging on the elastic and creep compliances were determined separately. In terms of the effective creep compliance, the effects of physical aging on creep behavior can be represented by momentary master curves. By the use of the superposition principle, each master curve can be shifted to collapse into the reference master curve (RMC) by introducing shift factors and shift rates for time. An effective time model was used for the long-term creep prediction. The effect of aging on relaxation time and shape factor was taken into account in the effective time model.