Impact of structure and relaxation on fatigue and micromechanical properties of oxide glasses - the role of volatiles and bonding state

由于亚临界裂纹扩展(SCCG)会使玻璃的抗拉强度降低许多数量级，因此在开发超强玻璃方面，改善疲劳性能的潜力是最有趣的。一个重要的瓶颈是对裂纹尖端大量相互作用的压力-温度和水影响的松弛现象和相关增韧策略的基本理解。因此，本提案旨在促进对由于裂尖挥发分集中和拉应力增加而引起的结构松弛效应和局部性质的基本理解。为此，将通过制备不同P-T历史的玻璃以及通过在压缩玻璃结构中掺入挥发物(重点是H2O)来在物理上设计玻璃拓扑。因此，该项目在第一个资助期由三个相互关联的实验任务组成：任务1)不同挥发份和不同P-T历史的玻璃的合成以及玻璃的结构和块体力学性能的表征，任务2)用机械能谱研究这些玻璃中的亚Tg驰豫过程，任务3)利用原位和非原位(压痕)技术进行裂纹形成和扩展的实验研究。SPP 1594中的合作将为将随时间变化的粘弹性特性应用于断裂力学的理论描述提供基础，并将提供亚Tg起始温度，用于对低至室温的拓扑约束进行建模。因此，该项目旨在促进对控制SCCG的局部松弛机制和氧化物玻璃的微观机械性能的基本理解，因为它们是开发无SCCG玻璃和玻璃表面的结构钢化设计的关键。

As subcritical crack growth (SCCG) can reduce tensile strength of glasses by many orders of magnitude, the potential for improvement of fatigue behaviour is most intriguing in developing ultra-strong glasses. An essential bottleneck is the basic understanding of the numerous interplaying pressure- temperature- and water- affected relaxation phenomena at the crack tip and related toughening strategies.Therefore, the present proposal aims to advance the basic understanding of structural relaxation effects and local properties caused by increased volatile concentration and tensile stresses at the crack tip. For this sake, glass topology will be designed physically by preparation of glasses of different P-T histories as well as compositionally by incorporation of volatiles (the focus will be on H2O) into the compressed glass structure. Both are expected to have a strong influence on the viscoelastic properties (complex moduli) of the near-tip glass structur.Therefore the project is composed in the first funding period by three interrelated experimental tasks: Task 1) Synthesis of glasses with different volatile contents and different P-T histories and characterization of structural and bulk mechanical properties of the glasses, Task 2) Studies of sub-Tg relaxation processes in these glasses by mechanical spectroscopy, Task 3) Experimental investigation of crack formation and propagation using in situ and ex situ (indentation) techniques. Cooperation within SPP 1594 will provide basis to implement time-dependent viscoelastic properties into theoretical descriptions of fracture mechanics and will deliver sub-Tg onset temperatures for modelling topological constraints down to room temperature. The project aims therefore to advance the basic understanding of the local relaxation mechanism controlling SCCG and micro-mechanical properties in oxide glasses as they are a key for structural toughening designs to develop SCCG-free glasses and glass surfaces.