Northeastern University

Materials Systems

CIRCS activities in this area focus on the development of state-of-the-art computational methods to understand the behavior of a wide range of technological materials and natural biomaterials such as bone. Processed materials range from structural alloys to nanomaterials with applications to transportation, power generation, solar energy harvesting and nanoelectronics. Methods span atomistic and continuum scales. The micro and nano structures of those materials is controlled to a large degree by complex systems of interfaces, including phase boundaries, grain boundaries, and cracks, and their interactions with materials defects such as dislocations, vacancies, and interstitials. Research in Karma's group from Physics is centered around the development of scale-bridging phase field methodologies to describe the complex non-equilibrium behavior and interaction of those interfaces and defects.

Karma's group is collaborating with the Shefelbine and Erb groups in engineering to understand toughness that is a material's ability to withstand fracture. In biological systems high toughness results from a composite microstructure combining soft flexible proteins with oriented hard mineral crystals. This project combines computational and experimental studies of crack propagation to determine the relative importance of material anisotropy and heterogeneities in crack path selection and fracture toughness. Novel synthetic discontinuous fiber composites are being produced whereby inhomogeneity and anisotropy of the composite can be tuned with a magnetic field and numerical simulations employing the phase field method are being used to predict complex crack paths in those materials.

Karma's group is also presently collaborating with Upmanyu's group from Mechanical and Industrial Engineering to combine atomistic and continuum scale simulation methods to explore the fundamental mechanisms that control the shape, size, and growth rate of semiconductor nanowires as a function of material parameters such as solid-vapour, solid-liquid, and liquid-vapour interfacial energy and mobility. Current investigations focus on the silicon-gold system. This research promises not only a major advance in our understanding of nanowire growth but also significant technological payoffs, including a design on new technological materials with extraordinary properties and new functionalities.