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Fatigue-crack growth simulations at the nanoscale are performed using anatomistic/discrete dislocation method at finite temperature. The generalmechanisms of the plastic deformation at the crack tip are studied in nickel andcopper single crystals. The dimensions of the specimens are in the range ofseveral hundred nanometers, and the fatigue loading is strain controlled underconstant and variable amplitude.From our simulations, the growth rates of nanocracks are found to becomparable to those of microscale cracks, but considerably larger than those oflong cracks. In addition, nanoscale cracks are found to grow at stress-intensityfactorranges well below the commonly accepted values for long crack. Thisclearly indicates that fatigue damage progression in metals involves multiscalephenomena such as accelerated growth rates for cracks in the nanometer rangethat cannot be neglected in the failure mechanism. The effects of temperatureand loading rate on the crack growth behavior are also investigated.