Collaborative Research: Understanding and Controlling the Resistance to Scratching in Alkali-Free Glasses

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With the advent of substrate glasses for LCD/OLED panels and damage-resistant protective covers for touch-screen computing devices, humans physically interact with glass surfaces now more than ever. However, the resulting risk for scratch-induced damage remains a key concern, which seriously limits glass's suitability to many applications. Indeed, residual troughs resulting from abrasion tend to impact the visual aspect of glasses, which, in turn, deteriorates their transparency. More importantly, the presence of surface damage greatly decreases glass's strength, thereby raising safety issues. To address these concerns, this research aims to reveal the physics of glass scratching in calcium aluminosilicate glasses, an archetypical model for alkali-free glasses used in display applications. This effort seeks to provide a science-based foundation to develop new glasses with tailored responses to scratching. This will contribute towards the advancement of national health, prosperity, and welfare, by allowing glasses to be designed and used for a broader range of applications with desired failure mechanisms, for example allowing screens on handheld computing devices to be more resistant to shattering. By integrating multiple disciplines, including physics, material science, and mechanics, this research will train a diverse group of students in various aspects of engineering and contribute to forming the next generation of scientists that the U.S. glass industry critically needs to compete globally. Additionally, the award will support several educational and outreach activities at both institutions, e.g., undergraduate research, female and minority student participation, and high school STEM events. Scratching remains one of the main types of surface damage and can greatly reduce the durability of a glass. Indeed, the radial and median cracks that often develop as a result of a scratching flaw act as stress amplifiers or singularities on the surface of glasses and, thereby, have a direct influence on glass's structural integrity by decreasing its mechanical strength. Yet, the mechanics of glass scratching has remained chiefly empirical thus far. To address this gap of knowledge, an integrated, multiscale approach relying on both computational and experimental tasks is planned to reveal the physics of scratching in alkali-free calcium aluminosilicate glasses. To this end, we adopt a multiscale, bottom-up approach wherein molecular dynamics simulations, structure characterization tests, and nanoscale mechanical experiments are used to inform continuum peridynamic models with the aim to deconstruct the contribution of each energy dissipation mechanism during scratching. The predictions from peridynamic models will be systematically validated by scratch testing. The handshake between multiple scales will provide some new fundamental knowledge serving as a guide to elucidate how the composition and atomic structure of a glass control the nature and extent of each energy dissipation mechanism that acts upon scratching.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.