Tracking the cracking

To become indestructible, glass must first be destroyed. Super-strong glass comes only from crack and break analysis.

To become indestructible, glass must first be destroyed. Super-strong glass comes only from crack and break analysis.

Glass has a remarkably high internal strength. Its weak points are small cracks on the surface or edges. These micro-defects, caused by production or handling, spread inward as mechanical stress increases, leading to sudden fractures in the brittle material.

More strength through ion exchange

Investigating this process has already led to successful increases in glass strength. Chemical tempering by means of ion exchange produces a compressive stress in the glass surface. This prevents cracks from propagation, making glasses more break-resistant. This method and others like it have led to the development of ultra-thin, high-strength glasses that can even be bent – innovative materials paving the way to the future of electronics, medicine and energy.

In his quest to strengthen glass, Dr. Sheldon M. Wiederhorn uses an element everyone knows: water. When water is introduced to quartz glass at temperatures of 200 degrees Celsius, the volume expands and ultimately strengthens the material. For decades, the American scientist has pioneered research in the field of crack formation and propagation. His work is fundamental in predicting such mechanical properties of glass – and in shifting its physical limits. In 2016, he and his colleagues Prof. Satoshi Yoshida and Dr. Jean-Pierre Guin received the 14th Otto Schott Research Prize in Sheffield, England, for their groundbreaking achievements in the field of glass strength.

Wide variety of analytic methods

While fundamental research looks deep into glass’s atomic nano- and microstructures, the analytics laboratories of industrial companies such as SCHOTT are also focusing on practical applications at the macro level. A comprehensive methodological repertoire is available to determine glass strength, hardness and wear, as well as fracture analysis (fractography) – from standardized stress tests and specially developed, application-specific tests to stereomicroscopic recognition and interpretation of characteristic fracture patterns. “Our analyses are reminiscent of forensic work – with a high level of clarification,” says a grinning Dr. Florian Maurer, SCHOTT Senior Scientist for strength and fractography.

Internal and external customers stand to benefit. For example, a numerical simulation can virtually model load distribution to improve the geometry and strength of pharmaceutical vials. Cutting technique analysis helps optimize the edge quality of glass microsheets. Ball drop and ring-on-ring tests measure the surface strength of glass and glass-ceramics. “The focus is always ultimately on root causes and probabilities of failure, forecasts on lifetime and reliability, consultation and support for better products and processes,” summarizes Dr. Maurer.

Even Dr. Wiederhorn, who also visited SCHOTT’s analytics laboratories in Mainz after receiving the Otto Schott Award, was impressed by the performance power: “Worlds truly lay between the methodology of yesterday and today. It is fascinating how precisely SCHOTT can measure cracks and crack growth in glass and evaluate it in such depth.” Research and practice, it seems, have a common goal: to better understand the nature of crack generation in glass, edging slowly closer to super-strength.

Fracture analyses of glass are
reminiscent of forensic work.”Dr. Florian Maurer, SCHOTT Senior Scientist

February 22nd, 2017


William James
Advanced Optics
SCHOTT North America, Inc.