Using Controlled Defects in Glass to Assess Strength

Brittle fractures are formed when a flaw is propagated to the point it exceeds the critical crack length for a given material, causing catastrophic failure almost immediately at that particular point. Similar brittle-fracture behavior is exhibited by glass that is used in an energy saving exterior glazing or in a touchscreen device. The probability of failure occurring in a piece of glass is correlated to the probability of a flaw of critical crack length existing in a zone of the glass under stress. The failure probability depends not only on the amount of stress or load applied to the piece of glass, but also on the glass flaw distribution.

Improving the Resistance to Glass Failure

To enhance the durability of the glass used in these types of critical applications, research should be carried out to;

1. Decrease the rate of sub-critical crack growth
2. Increase the critical crack length
3. Restrict the propagation of a crack that may otherwise cause a catastrophic failure

For this purpose, various approaches are being studied:

• Coatings
• Microstructural and/or processing changes
• Compositional modifications

Research Tools Available

A process of providing controlled defects in glass (Figure 1) can be employed to help the research and evaluation of methods to enhance the glass fracture resistance. The effect of different treatments can be assessed by introducing known defects into glass samples of reasonable statistical size (for instance 10) and fracturing them under familiar, controlled conditions.

Figure 1. Creating controlled defects in glass.

Bruker’s UMT, featuring a standard diamond tip such as a Rockwell indenter, can be employed to impart scratches of repeatable and precise depth and length under servo-feedback controlled conditions. Following this, a 3-point bend fixture (Figure 2) can also be mounted on the UMT to fracture the glass under controlled conditions.

Figure 2. 3-point bend fixture for glass testing.

This information has been sourced, reviewed and adapted from materials provided by Bruker Nano Surfaces.

For more information on this source, please visit Bruker Nano Surfaces.