Influence of Structure and Topology on the Deformation Behavior and Fracture of Oxide Glasses

Abstract

Oxide glasses are ubiquitous in daily life. They have proven useful as bioactive materials, optical fibers, flexible substrates and displays, solar modules, and many other applications. This enormous number of current applications is due to the sheer number of possible compositions made by the possibility of combining different elements from the periodic table. Nevertheless, their usage is limited by their brittleness and low resistance to damage due to the lack of large and clear deformation (shearing) mechanisms to dissipate stress. Computer simulations, including atomistic simulations, serve as an important tool to understand and reveal the deformation mechanisms at atomic and nanometric scales, thus guiding the development and design of glasses with superior properties. The objective of this thesis are to understand the role of structure, modifiers, and processing on oxide glasses’ deformation and fracture behavior. Large-scale atomistic simulations were performed to reveal these deformation mechanisms at the atomic scale in binary metaphosphate glasses modified with different modifiers, silica, and sodium silicate glasses with varying sodium content. The effect of modifier type on deformation-induced structural anisotropy and deformation behavior was studied in metaphosphate glasses. On the other hand, the effect of the modifier content and topology on the deformation behavior and fracture was investigated in sodium silicate glasses. In the metaphosphate glasses, the presence of modifiers with high field strength leads to higher mechanical properties when compared to glass compositions with low field strength modifiers. The origin of the structural transient and persistent anisotropy observed in all metaphosphate glasses was shown to be the same, which was discussed at different structural levels. At the short-range structure, it originates from the alignment of P–O bonds. The next structural level involving neighboring tetrahedra is captured by the orientation of the P–P bonds. These short-range alignments of the P–O and P–P bonds lead to the changes in the medium-range order as captured by the orientation of the chain along the tensile axis and orthogonal to the loading axis. The tensile Young’s moduli of the anisotropic glasses obtained by either pre-tension or pre-compression measured along the pre-deformation axis is lower than the pristine glass due to a stretching of the structure as indicated by the remaining plastic strain. The tensile Young’s moduli of the pre-deformed metaphosphate glasses by pre-tension showed a higher Young’s modulus than the glasses pre-deformed in compression when measured in the same direction as the pre-deformation one. On the other hand, understanding the mechanical behavior of silicate glasses with different compositions and pre-loading modes is highly relevant to many technological applications. Therefore, silicate glasses with different compositions and subjected to different type of deformations at room temperature were studied. The atomic-scale mechanisms of the deformation of these glasses showed that during compression and shear at higher strains, a significant number of atoms that switched bonds was found, which was not the case in tension due to the fracture of the samples. These atoms that have a change in their bonding topology are localized within shear bands in the shear deformation and are homogeneously distributed in samples deformed in compression. The tensile mechanical behavior of the predeformed glasses showed that the pre-deformation decreased the material strength, and an increasing ductility was observed in the case of pre-compression. This originates from a homogeneous persistent change in the bonding with pre-compression, which was not the case on pre-tension and pre-shear. The tensile deformation mechanism of pre-deformed glasses was found to be due to the appearance and coalescence of cavities during the deformation. The presence of these cavities is affected by both composition and pre-deformation, which was also discussed for the first time at the atomic scale. The results presented in this thesis highlight the importance of the local events in controlling the macroscopic glass properties. Thus, providing insights at the atomic scale needed for further development of oxide glasses.

Recommended citation: Influence of Structure and Topology on the Deformation Behavior and Fracture of Oxide Glasses, Doctoral thesis, 2023.
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🇬🇧 English
This research investigates how the internal structure and connectivity of oxide glasses influence their mechanical behavior and how they fracture. Using advanced computer simulations, the study analyzed how different types of modifiers and pre-deformation affect the properties of metaphosphate and silicate glasses. Key findings reveal that modifiers with higher field strength enhance mechanical properties, and that structural anisotropy arises from the alignment of atomic bonds under stress. The research also found that pre-deformation can alter a glass's response to stress, leading to changes in its strength and ductility. These insights are crucial for designing new glasses with improved performance for various technological applications, from electronics to advanced materials. The study's findings have significant implications for materials science and engineering. By understanding the atomic-level mechanisms behind glass deformation and fracture, scientists can develop more robust and reliable glass materials. This could lead to advancements in areas like stronger smartphone screens, more efficient optical fibers, and safer nuclear waste containment. The research also highlights the potential for tailoring glass properties through precise control of their composition and structure, paving the way for novel glass designs with specific, desirable characteristics.

🇸🇦 العربية
يبحث هذا البحث في كيفية تأثير التركيب الداخلي واتصال الزجاج الأكسيدي على سلوكه الميكانيكي وكيفية تكسره. باستخدام محاكاة حاسوبية متقدمة، حللت الدراسة كيف تؤثر أنواع مختلفة من المعدلات والتشوه المسبق على خصائص زجاج الميتافوسفات والسيليكات. تكشف النتائج الرئيسية أن المعدلات ذات قوة المجال الأعلى تعزز الخصائص الميكانيكية، وأن عدم التماثل الهيكلي ينشأ من محاذاة الروابط الذرية تحت الضغط. وجدت الدراسة أيضًا أن التشوه المسبق يمكن أن يغير استجابة الزجاج للضغط، مما يؤدي إلى تغييرات في قوته وقابليته للتشوه. هذه الأفكار حاسمة لتصميم زجاج جديد بخصائص محسنة لمختلف التطبيقات التكنولوجية، من الإلكترونيات إلى المواد المتقدمة. نتائج الدراسة لها آثار كبيرة على علوم وهندسة المواد. من خلال فهم الآليات على المستوى الذري وراء تشوه الزجاج وتكسره، يمكن للعلماء تطوير مواد زجاجية أكثر قوة وموثوقية. يمكن أن يؤدي هذا إلى تقدم في مجالات مثل شاشات الهواتف الذكية الأكثر قوة، والألياف البصرية الأكثر كفاءة، واحتواء النفايات النووية الأكثر أمانًا. يسلط البحث الضوء أيضًا على إمكانية تخصيص خصائص الزجاج من خلال التحكم الدقيق في تركيبه وهيكله، مما يمهد الطريق لتصميمات زجاجية جديدة ذات خصائص محددة ومرغوبة.

🇫🇷 Français
Cette recherche examine comment la structure interne et la connectivité des verres d'oxyde influencent leur comportement mécanique et leur mode de rupture. À l'aide de simulations informatiques avancées, l'étude a analysé comment différents types de modificateurs et de pré-déformations affectent les propriétés des verres de métaphosphate et de silicate. Les principales conclusions révèlent que les modificateurs à champ de force plus élevé améliorent les propriétés mécaniques, et que l'anisotropie structurelle découle de l'alignement des liaisons atomiques sous contrainte. La recherche a également révélé que la pré-déformation peut modifier la réponse d'un verre à la contrainte, entraînant des changements dans sa résistance et sa ductilité. Ces aperçus sont cruciaux pour la conception de nouveaux verres aux performances améliorées pour diverses applications technologiques, de l'électronique aux matériaux avancés. Les conclusions de l'étude ont des implications significatives pour la science et l'ingénierie des matériaux. En comprenant les mécanismes au niveau atomique derrière la déformation et la fracture du verre, les scientifiques peuvent développer des matériaux vitreux plus robustes et fiables. Cela pourrait conduire à des avancées dans des domaines tels que des écrans de smartphone plus résistants, des fibres optiques plus efficaces et un confinement plus sûr des déchets nucléaires. La recherche souligne également le potentiel de personnalisation des propriétés du verre par un contrôle précis de sa composition et de sa structure, ouvrant la voie à de nouvelles conceptions de verre aux caractéristiques spécifiques et désirables.

🇩🇪 Deutsch
Diese Forschung untersucht, wie die innere Struktur und Konnektivität von Oxidgläsern ihr mechanisches Verhalten und ihre Bruchmechanismen beeinflussen. Mithilfe fortschrittlicher Computersimulationen analysierte die Studie, wie verschiedene Arten von Modifikatoren und Vorverformungen die Eigenschaften von Metaphosphat- und Silikatgläsern beeinflussen. Wichtige Ergebnisse zeigen, dass Modifikatoren mit höherer Feldstärke die mechanischen Eigenschaften verbessern und dass strukturelle Anisotropie aus der Ausrichtung atomarer Bindungen unter Spannung resultiert. Die Forschung ergab auch, dass Vorverformung die Reaktion eines Glases auf Spannung verändern kann, was zu Änderungen seiner Festigkeit und Duktilität führt. Diese Erkenntnisse sind entscheidend für die Entwicklung neuer Gläser mit verbesserten Eigenschaften für verschiedene technologische Anwendungen, von Elektronik bis hin zu fortschrittlichen Materialien. Die Ergebnisse der Studie haben bedeutende Auswirkungen auf die Materialwissenschaft und die Ingenieurwissenschaften. Durch das Verständnis der atomaren Mechanismen hinter Glasdeformation und -bruch können Wissenschaftler robustere und zuverlässigere Glasmaterialien entwickeln. Dies könnte zu Fortschritten in Bereichen wie stärkeren Smartphone-Bildschirmen, effizienteren Glasfasern und einer sichereren Eindämmung von Atommüll führen. Die Forschung unterstreicht auch das Potenzial zur Anpassung von Glaseigenschaften durch präzise Kontrolle ihrer Zusammensetzung und Struktur, was den Weg für neuartige Glasdesigns mit spezifischen, wünschenswerten Merkmalen ebnet.