AsianScientist (Feb. 14, 2022) – Water and humidity can aggravate surface cracks on tempered and annealed glass, turning tiny flaws into large fractures. Reported in the Journal of the European Ceramic Society by researchers from South Korea, the findings could provide insights into building safe and better construction practices.
Pelted by wind, rain, and other particles, glass windows on buildings often sustain microcracks on their surface. For example, a gust of wind can send sharp-edged sand particles flying against a window, producing tiny flaws. While the initial impact may be small and even invisible to the naked eye, water droplets and atmospheric humidity can widen or deepen the cracks.
Known as stress corrosion or subcritical crack growth (SCG), environmentally-enhanced cracking can degrade the mechanical strength of a glass structure. As a result, the glass becomes prone to further damage, raising safety concerns for high-rise buildings.
To better understand SCG, a research team from Pusan National University South Korea’s Busan city explored water-promoted cracking behavior on glass surfaces. While past studies have focused on how quickly a crack lengthens or wides on annealed glass, their study was the first to compare the effects of water on crack propagation between annealed and tempered glass.
Using a Vickers indenter, an instrument for testing the hardness of a material, the researchers produced artificial microcracks on a glass surface and exposed the samples to atmospheric humidity and water. Strikingly, water-induced SCG in annealed glass made the cracks significantly longer compared to that of tempered glass.
Then, immersing the samples in water for 24 hours led to the formation of lateral cracks in tempered glass, suggesting signs of water intrusion. Meanwhile, the annealed glass showed radial cracks, which typically indicate high stresses at a central point from which the fractures extend outward. As water seeps into the cracks, it dissolves the chemical bonds holding the glass network together, degrading the strength of the structure.
While the study provides new insights into how water further damages a cracked glass, the researchers highlight the need for further investigation into the mechanisms behind the varying cracking behaviors. They hope their findings can help glass designers and engineers devise interventions to minimize shattering of the glass exteriors.
“With an increase in typhoon and storm frequencies due to global warming, we need to find out new ways to protect the exterior of glass windows,” said corresponding author Professor Park Sang-Hu.
The article can be found at: Kim & Park (2021). Vickers crack extension and residual fracture strength of annealed and thermally tempered glass in water.
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Source: Pusan National University; Photo: MaxWdhs/Pixabay.
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