Marisol Koslowski Purdue University Understanding the effect of the microstructure on the material response is essential to advance the design and reliability in a variety of engineering applications. Multiscale simulations bring the opportunity to realize the relation between microstructure and mechanical behavior and can be exploited to understand the sensitivity of the mechanical properties of materials to the microstructure variability. I will present numerical simulations with a phase field dislocation dynamics model to study the effect of the initial microstructure, i.e., grain size, grain size distribution, grain boundary energetics and initial dislocation density, on the mechanical response of nanocrystalline (nc) nickel. In particular, the sensitivity of creep deformation and the yield stress on the microstructure. This work reveals that the grain size distribution and the initial the dislocation density have a significant influence on the yield stress for grain sizes under 32 nm and that the average grain size is not enough to characterize the microstructure. Simulations with zero initial dislocation density exhibit almost size independent stress-strain behavior, while Hall-Petch effect is observed in simulations with non zero initial dislocation density. To study creep deformation dislocation dynamics simulations are coupled to a Kinetic Monte Carlo algorithm. We observe that the creep rate is strongly dependent on the grain size distribution. We obtain a stress exponent in the range 4 to 5 in very good agreement with experimental measures of dislocation driven creep deformation.