Fracture Toughness of Silicate Glasses: Insights from Molecular Dynamics Simulations
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Fracture Toughness of Silicate Glasses: Insights from Molecular Dynamics Simulations Yingtian Yu,1 Bu Wang,1 Young Jea Lee,1 and Mathieu Bauchy1 1 Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, United States ABSTRACT Understanding, predicting and eventually improving the resistance to fracture of silicate materials is of primary importance to design new glasses that would be tougher, while retaining their transparency. However, the atomic mechanism of the fracture in amorphous silicate materials is still a topic of debate. In particular, there is some controversy about the existence of ductility at the nano-scale during the crack propagation. Here, we present simulations of the fracture of three archetypical silicate glasses using molecular dynamics. We show that the methodology that is used provide realistic values of fracture energy and toughness. In addition, the simulations clearly suggest that silicate glasses can show different degrees of ductility, depending on their composition.
INTRODUCTION Brittleness is the main limitation of glasses, as impacts, scratches or vibrations can result in undesirable or even dangerous fracture. Indeed, glasses lack a stable shearing mechanism, thus showing very poor ductility and, consequently, high brittleness [1, 2]. This is a serious safety concern, as the number of injuries related to glass (e.g., during car crashes or by broken bottles) is significant. Further, improving the mechanical properties of glasses is crucial to address major challenges in energy, communication and infrastructure arenas [3]. For example, strength, toughness and stiffness are a major bottleneck for further development of short-haul highcapacity telecommunication and fiber-to-the-home technologies, flexible substrates and roll-toroll processing of displays, solar modules, planar lighting devices, the next generation of touch screen devices, large scale and high altitude architectural glazing, ultra-stiff composites and numerous other applications. Increasing the strength and toughness of glass would not only enable new applications, but also lead to a significant reduction of material investment for existing applications while achieving comparable performances [4]. To improve the ductility of glasses, current techniques focus on compositing [5], inclusion of holes [6] or surface treatments [7]. However, these treatments often result in undesirable side effects such as a loss of transparency [3]. An alternative option is to enhance the intrinsic ductility of glasses by tuning their atomic topology, which is mainly a function of their composition. Such intrinsic optimization, which has been established as a Grand Challenge for glass [4], is the focus of the present study. Fulfillment of this goal requires elucidation of the atomistic mechanism of fracture in glasses. Indeed, although glasses are typically brittle materials at the macro-scale, there remains some controversy about the existence of ductility at the nano-scale. Hence, as opposed to an
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