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：玻璃有许多重要的应用，因为它们是透明的，成本低，重量轻，可以大量生产和快速。它们有一个缺点：缺乏高机械强度。有一些方法可以使玻璃更坚固，如快速冷却称为回火，用于制造更坚固的窗玻璃或离子交换法，用于制造更坚固的智能手机触摸屏。然而，这些方法并不适用于所有的玻璃，不能用于制造更强的硅玻璃光纤。探索了一种适用于各类玻璃的新型玻璃强化方法。技术细节：大气中的水蒸气会影响玻璃的表面特性。当玻璃受到低于可使玻璃破裂的临界应力的拉应力时，在低于玻璃化转变温度的适当温度下，部分表面拉应力受水分的影响而松弛。当施加的拉伸应力被去除时，玻璃表面获得残余压应力。得到的玻璃样品比以前更坚固，因为需要更大的拉应力，以克服产生的表面压应力，使玻璃破碎。通过澄清水促进表面应力松弛和控制表面残余应力产生动力学的机制，可以选择最佳温度、时间、拉伸应力和水分含量来生产高强度玻璃。具体来说，在拉伸应力和水蒸气作用下加热产生的二氧化硅玻璃光纤中，亚微米厚表面残余应力的大小可以通过切片纤维的弯曲和FTIR反射光谱来估计，并将结果与测量的纤维机械强度进行比较。此外，所提出的玻璃强化机理可以解释玻璃科学中一些长期存在的谜团。例如，玻璃中的裂纹可以在低拉伸应力下生长。然而，当玻璃首先受到低拉应力时，不会引起裂纹扩展，然后再受到原始拉应力，裂纹就不会扩展。显然，玻璃在亚临界拉伸应力作用下变得更强，但目前还没有令人信服的解释。本研究培养了两名研究生和两名本科生，该研究课题结合了玻璃科学与技术的探索。