Fatigue Damage and Degradation in Random Short-Fiber SMC Composite

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Abstract
Damage accumulation and cyclic degradation in a random short-fiber SMC com posite subjected to tensile fatigue loading are studied. Fatigue damage in various forms of microcracking is examined. The transient nature of the nonlinear, monotonic stress- strain curve is investigated first, and subsequent property degradation and hysteresis loop changes are examined. Contrary to the behavior of certain metals and polymers, a cyclic stable state is never reached in general; cyclic softening is always observed in this class of materials. Owing to the random microstructure of the SMC material, the fatigue damage is viewed as being macroscopically homogeneous and uniform, and the damage growth is treated in a continuous sense. A parameter is then introduced to define the degree of the homogeneous damage. A power-law relationship among the rate of damage evolution, loading variables, and cyclic history is established. The homogeneous fatigue damage decreases rapidly with the loading cycle due to combined effects of rapid depletion of microcrack initiation sites and presence of various crack arrest mechanisms.

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