Larger-scale phenomena are computed from smaller-scale phenomena and first principles.

Progress has been made in research on several fronts in an effort to develop computational simulation capabilities for use in virtual design and testing of advanced structural materials. It is envisioned that the capabilities will be embodied in a coherent set of methods, software to implement the methods, and advances in the fundamental understanding of many issues in the thermomechanical performance of materials. It is further envisioned that the methods and software will be organized into a hierarchy (see figure) corresponding to a hierarchy of spatial scales from electronic through atomic, mesoscale, microstructural, and continuum to macrostructural, and that there will be seamless coupling of information from each scale to the next larger scale. A secondary objective of this research and development effort is to provide direct simulation output at each level of the hierarchy for investigating specific phenomena at the corresponding spatial scale. For the purposes of demonstrating the capabilities and providing specific focus for the overall research, it is intended to predict nano-, micro-, and macroscopic degradation of aluminum and titanium alloys under fatigue loading and in a corrosive (oxidative) environment and as a function of temperature.

Computational Simulations are performed by different methods at different spatial scales. Results obtained at each scale are, variously, fed the next larger scale or taken as direct output.

• The first discrete-dislocation model for predicting fatigue-crack-growth behavior with no a priori assumptions about fatigue. The approach taken in developing this model was to directly address the mechanics and other aspects of the applicable physics of plastic deformation at the individualdislocation level.


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