A model for the longitudinal primary creep of a long-fiber composite

The longitudinal primary creep of long-fiber composites is modeled by consi dering the transient stress states arising From load transfer from the weak er matrix phase to the stronger fiber phase as the composite transitions fr om the elastic stare present immediately after loading to steady-state stag e where both phases creep. The effect of primary creep of each of the phase s on the primary creep of the composite is also taken into account. The mod el is evaluated for the NiAl-N system for which the primary creep of tungst en fibers is quite significant. The composite primary creep strain is predi cted to be significant at high applied composite stresses and for high fibe r volume fractions and primary creep time is found to be uniquely related t o the composite steady-state creep rate. The model is verified with 1025 de grees C compressive creep experiments in the NiAl-W composite system. Good agreement between model predictions and experiments is obtained when the ob served composite steady-state creep behavior converges to the steady-state predicted for materials in which both phases experience creep deformation. (C) 1999 Arm Metallurgica lire. Published by Elsevier Science Ltd. All righ ts reserved.