Advancing and accelerating materials discovery depends on our ability to develop models that can allow rapid investigation of large materials spaces to optimize properties, and to design manufacturing processes that yield the desired mechanical behavior on the basis of verifiable simulations. Of particular interest are the material properties of systems which consist of multiscale structural components whose dimensions lie in the range of a few nanometers to a few hundred micrometers. This includes micro-electro-mechanical systems, micro implants and microelectronic devices. At small length scales the measured mechanical properties vary significantly with decreasing dimensions. While existing models can predict deterministic values, analytical models often implicitly assume that noise in the data is due to difficulties inherent in microscale testing techniques. However, experiments show a significant amount of stochastic behavior no matter how elegantly the experiments are performed. This award supports fundamental research to develop predictive models that account for stochastic phenomena to ensure that validation techniques and simulation tools are well paired. Further broader impact will be the creation of a diverse environment in our laboratories in terms of race, gender, and national origin. This project offers students and junior researchers opportunities to participate in a research and education experience in an interdisciplinary environment, tackling their thesis problems with co-advisement from faculty drawn from both mechanics and materials science.
The research activities will develop mechanics and materials science theories and testing schemes as metrics for material modeling and experimental validation. Our hypothesis is that plastic deformation in small volume is stochastic, serrated and heterogeneous. Such effects would arise from the stochastic nature of the underlying microstructure such as dislocations, grain size, interfaces and grain boundaries, from stress gradients arising from loading conditions and morphological defects, and the formation of localized and dislocation patterns. We will develop models that account for such phenomena so that validation techniques and simulation tools are well paired. Towards this end, this project will address the following five questions. 1) What are the underlying causes of the observed stochastic phenomena: onset of plasticity, localization, patterning, and serrated flow? 2) How do deformation mechanisms and defect-surface interactions contribute to strength, toughness, and damage in small volumes? 3) Under what morphological and microstructural conditions does the deformation behavior transition from deterministic to stochastic? 4) How can we quantify and model stochastic behavior across length scale? 5) How can we translate this understanding into a mesoscale stochastic size-dependent plasticity model?
