The capability to evaluate and model how metal deforms has benefited the manufacture and processing of the metals industry for decades. A predictive model that can be used to assess the evolution of stress/strain in a polycrystalline metals is desired as it will enable more accurate predictions of stress concentrations, damage nucleation, and material life spans. One of the major challenges in the development of such a model is understanding how plastic deformation flows through grain boundaries (such phenomenon is called slip transfer) and how the stress and strain fields are altered by slip transfer in the vicinity of the boundary. We attempted to overcome this challenge. In the current study carefully designed experiments and calibrated simulations are used to address this challenge. A novel approach is used to study the interaction between slip and grain boundaries using bi-crystal nanoindentation. By placing nanoindents at varying distances from grain boundaries and measuring the resulting indent surface topographies using atomic force microscopy (AFM), the influence of grain boundaries on the development of indent surface topographies is assessed and related to a variety of slip transfer metrics. To further analyze the stress, strain, and shear of individual slip system in the bi-crystal nanoindentation, a crystal plasticity finite element (CPFE) models was built to simulate indentation near a grain boundary. The model was calibrated using experimentally measured parameters and successfully captured most of the features in the experiments. Nonetheless, strict point-to-point comparisons between experimentally measured and simulated indent topographies revealed some discrepancies, in that the model is less accurate in the vicinity of grain boundaries than in the grain interiors. To evaluate slip transfer and the local stress evolution in a fully quantitative manner, a predictive model was developed that is capable of resolving slip accommodation of multiple systems involved in the process. Slip trace analysis was combined with AFM and electron backscattered diffraction (EBSD) to analyze the slip accommodation observed at multiple grain boundaries. Based on all the experimentally observed slip transfer cases, a new iterative stress relief (ISR) model was developed. The ISR model, validated by experimental observations, features the ability to predicting multiple accommodating slip systems in a slip transfer and assessing the evolution of local stress state. In addition, a set of critical resolved shear stress (CRSS) ratios were obtained by minimizing the discrepancies between observations and model predictions. This work has furthered the understanding of slip transfer/accommodations and the influence of local stress evolution on the slip transfer in the community. The ISR model has been proved to be very successful in the studied material system, but has yet to be tested under different conditions.
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