High Performance Glasses with Pressure-Induced Topological Changes

Glasses with high damage resistance are critical for military armor applications. In this project, we propose to develop a novel family of glasses having exceptionally high intrinsic damage resistance. These glasses will enable lightweight anti-ballistic armor by tailoring the glass network at the atomic scale to introduce deformation modes that can dissipate applied energy without the introduction or propagation of strength-limiting cracks. Our project will build a comprehensive understanding of the atomic-scale mechanisms for the improved damage resistance, including its dependence on glass chemistry and thermal history.The project involves a combination of experimental glass-melting and characterization, together with atomic-scale molecular simulations of the glass structure, network topology, and mechanical properties. Building upon previous work by the PI, the glasses with intrinsic damage resistance are adaptive materials that can dynamically adjust their structure and network topology in response to an applied stress. These glasses contain an open, fully connected network structure with a high concentration of boron oxide in a threefold coordination state.The threefold-coordinated boron can dynamically convert to fourfold coordination in response to applied stress. As the boron coordination increases, the hardness of the glass dynamically increases under the load. The adaptable glass network leads to a suppression of lateral cracking, improving the retained strength of the glass.The project will be executed along four workstreams to investigate: (A) the role of topological changes in promoting damage resistance, (B) glass chemistry design and optimization, (C) the role of the nonequilibrium thermodynamic state of glass in enhancing damage resistance, and (D) the nonlinear advantage in damage resistance which can be obtained by superimposing a compressive stress profile onto a glass with an adaptable network. These workstreams will involve a close coupling of experimental research and atomic-scale modeling using newly developed potentials for the molecular dynamics simulations.The output from the project will be a deep fundamental understanding of the atomistic mechanisms for the improvedperformance of glasses with high intrinsic damage resistance. The project will fund one Ph.D. student for three years to focus on the experimental and theoretical aspects of the project. Through this project, the student will be well-versed in both experimentaland theoretical research, bridging the usual gap between experiment and theory. This research will advance fundamental science that is closely aligned with ONR goals as well as allow for specific DoD design input for targeted applications that facilitate currentand adapting needs of the ONR.