NSF/DMR-BSF: Bridging the gap between atomistic simulations and fracture mechanics

NONTECHNICAL SUMMARY

The National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Division of Materials Research funds this award, which supports research and education on the fundamental nature of fracture in materials, which is governed by processes that occur at the atomic scale.

The project seeks to answer the following question: why do atomistic simulations predict cracks in materials with different characteristics than those predicted by theory and observed in experiments? The PIs postulate that this is because, up until now and due to computational limitations, most atomistic simulations are artificially constrained and study systems that are too small. To go beyond current capabilities, the PIs will extend and apply a novel computational approach that will enable realistic simulations of fracture experiments. The simulations will focus on silicon, and will be validated against unique high-resolution dynamic fracture experiments performed by the Israeli collaborator. Silicon was chosen due its importance in many technologies including microelectronics devices, micro- and nano-electro-mechanical systems, solar cells, and bio-inspired devices.

This research has potential for a significant positive impact on industry by elucidating how to prevent catastrophic failure in devices. All computer codes developed in this project will be made freely available to the research community via dedicated web portals (qcmethod.org and openkim.org). The collaborative project will also strengthen research ties between the US and Israel, and engage Israeli graduate students (both Jewish and Arab) with their US counterparts to create a positive example of collaboration in a troubled region.

TECHNICAL SUMMARY

The National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Division of Materials Research funds this award, which supports research and education on the fundamental nature of fracture in materials, which is governed by processes that occur at the atomic scale.

The ultimate aim of this project is to develop a predictive multiscale framework for simulating fracture phenomena that explicitly account for the effect of a variety of factors including crystallographic orientation, loading rate, temperature, and preexisting defects. This requires a multiscale approach that includes both the correct treatment of the long-range stress field generated by a crack, and the atomic-scale fracture processes that involve bond breaking at the crack tip. Fully-atomistic simulations that focus primarily on the crack tip region exhibit an effect called 'lattice trapping' whereby the loading device has to overcome an energy barrier associated with breaking atomic bonds that span the cleavage plane. This overloading causes cracks to begin to move at high initial speed. In contrast, continuum theory does not account for lattice trapping and predicts that a crack can begin to propagate at any speed. Recent high-resolution fracture experiments on silicon crystals performed by the Israeli collaborator agree with continuum theory, and show that the lattice trapping effect is small and that slow initial crack speeds are possible. The PIs posit that lattice trapping is an artifact of the size and 2D constraints imposed on the atomistic simulations. The proposed framework will make it possible to simulate fracture experiments at realistic loading rates for specimens with a large enough atomistic region for curvature effects to occur.

This research has potential for a significant positive impact on industry by elucidating how to prevent catastrophic failure in devices. All computer codes developed in this project will be made freely available to the research community via dedicated web portals (qcmethod.org and openkim.org). The collaborative project will also strengthen research ties between the US and Israel, and engage Israeli graduate students (both Jewish and Arab) with their US counterparts to create a positive example of collaboration in a troubled region.