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Materials Science and Engineering, University of Michigan

  MSE / Research / Projects / CAREER: Theory and Simulation of the Structure and Mechanical Properties of Non-crystalline Solids

CAREER: Theory and Simulation of the Structure and Mechanical Properties of Non-crystalline Solids
Materials: Organic Metals
Application: Structural
Technique: Computation
Non-crystalline solids, also known as glasses, are found amongst all types of materials including semiconductors, ceramics, polymers and, more recently, metals. These non-crystalline metals, referred to as bulk metallic glass (BMG) alloys, have only been successfully produced in the last twenty years, and they show great promise as high strength, fracture resistant structural materials. However, a number of critical issues need to be resolved before these materials will achieve widespread commercialization. Amongst these is the fact that metallic glasses typically deform by shear localization. Under an applied load the metallic glass forms nearly atomically thin bands called shear bands along which the material slips, much like an earthquake fault. Shear bands are often observed to cause the ultimate failure of the BMG. Our research group is one of the first to observe shear localization in an MD computer simulation of a simple analog of a metallic glass. Reproducing this phenomenon in the computer has allowed us to make new observations regarding the atomic scale structures that lead to this failure mode.

Another important factor limiting more widespread use of non-crystalline solids for structural applications is the difficulty determining the quality of materials. Crystals reveal their structure when light, x-rays or electrons are scattered from their orderly structure. These same methods do not provide enough information to reliably predict properties of non-crystals or to analyze the result of various processing methods. New microscopies are in development to allow researchers to extract information on the angles between bonds, mutual alignment of bonds and other more subtle signatures. This research project aims to draw a rigorous connection between this information and changes in glass structure. Our research group has created a variety of glass samples in the computer by simulating cooling them quickly from different equilibrium liquid temperatures. Simulated tests are performed on these glasses and their structure is analyzed. These simulations have revealed that the short-range order in the atomic structure is sensitive to the preparation of the glass and to the degree of shear imposed. The percolation of this short range appears to be closely associated with the development of shear bands during mechanical loading.
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