Surface Stress Relaxation and Resulting Residual Stress in Glass: A New Mechanical Strengthening Mechanism of Glasses

玻璃中的表面应力松弛和由此产生的残余应力：一种新的玻璃机械强化机制

• 批准号: 1265100
• 负责人: Minoru Tomozawa
• 金额: $ 67万
• 依托单位: Rensselaer Polytechnic Institute
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1265100&HistoricalAwards=false
• 关键词: Surface; Stress; Relaxation; Resulting; Residual

NON-TECHNICAL DESCRIPTION: Glasses have many important applications because they are transparent, low cost, light-weight, and can be produced in large quantities and rapidly. They have one drawback: a lack of high mechanical strength. There are some methods to make glasses stronger such as rapid cooling called tempering which is used to make stronger window glasses or the ion-exchange method which is used to make stronger touch screen for smart phones. However, these methods are not applicable to all glasses and cannot be used, for example, to make stronger silica glass optical fibers. A new glass strengthening method, which can be used for all types of glasses, is explored.TECHNICAL DETAILS: Water vapor in the atmosphere can affect the glass surface characteristics. When a glass is subjected to a tensile stress below the critical stress which can break the glass, at an appropriate temperature below the glass transition temperature, some of the surface tensile stress is relaxed by the influence of moisture. When the applied tensile stress is removed, the surface of the glass acquires a residual compressive stress. The resulting glass sample is stronger than before, because a greater tensile stress is required, in order to overcome the generated surface compressive stress, to break the glass. By clarifying mechanism by which water promotes surface stress relaxation and controls the kinetics of surface residual stress generation, an optimum temperature, time, tensile stress, and moisture content can be chosen to produce high strength glasses. Specifically, the magnitude of a sub-micrometer thick surface residual stress in silica glass optical fiber, produced by heating under a tensile stress and water vapor, can be estimated by using both the bending of sliced fibers as well as FTIR reflection spectroscopy and the result compared with the measured mechanical strength of the fibers. Furthermore, the proposed mechanism of glass strengthening can explain some long-standing mysteries in glass science. For example, a crack in a glass can grow under a low tensile stress. However, when the glass was first subjected to a low tensile stress, one which does not cause crack growth, and then subjected to the original tensile stress, the crack does not grow. Apparently, the glass became stronger by a sub-critical tensile stress application, but no convincing explanation exists at the present. In this research two graduate students and two undergraduates are trained on this research topic which combines exploration of the science and technology of glasses.

非技术描述：眼镜具有许多重要的应用，因为它们是透明，低成本，轻巧的，并且可以大量生产，并且可以迅速生产。他们有一个缺点：缺乏高机械强度。有一些方法可以使眼镜更强大，例如快速冷却称为回火，用于制作更强的窗玻璃或用于制作智能手机更强触摸屏的离子交换方法。但是，这些方法并不适用于所有眼镜，也不能使用，例如使二氧化硅玻璃光纤更强。探索了一种新的玻璃强化方法，该方法可用于所有类型的玻璃。技术细节：大气中的水蒸气会影响玻璃表面特征。当玻璃在临界应力以下的拉伸应力下施加拉伸应力时，在玻璃过渡温度以下的适当温度下会破坏玻璃时，某些表面拉伸应力会因水分的影响而放松。当去除施加的拉伸应力时，玻璃的表面会获得残留的压力应力。所得的玻璃样品比以前更强，因为需要更大的拉伸应力，以克服产生的表面压力应力以破坏玻璃。通过阐明水促进表面应力松弛的机制并控制表面残留应力产生的动力学，最佳温度，时间，拉伸应力和水分含量可以选择产生高强度玻璃。具体而言，可以通过使用切片纤维的弯曲以及FTIR反射光谱光谱和结果与纤维测量的机械强度相比，可以估算二氧化硅玻璃光纤厚的厚度表面残留应力，该硅玻璃光纤纤维的厚度残留应力。此外，提出的玻璃加强机制可以解释玻璃科学中的一些长期谜团。例如，玻璃中的裂缝可以在低拉伸应力下生长。但是，当玻璃首先承受低拉伸应力时，不会导致裂纹生长，然后遭受原始的拉伸应力，裂纹不会生长。显然，玻璃通过亚临界拉伸压力的应用变得更加强大，但目前尚无令人信服的解释。在这项研究中，两位研究生和两名本科生接受了该研究主题的培训，结合了对眼镜科学和技术的探索。