What controls the strength of glasses What can be done to en

What controls the strength of glasses? What can be done to enhance the strength of silicate glasses? What controls the strength of thermoset polymers? What can be done to enhance their strength?

Solution

The strength of glasses is primarily controlled by the size and distribution of defects in the material. Unlike ductile materials, that undergo ductile fracture even when small defects are present, brittle materials such as glass are highly susceptible to fracture due to stress concentrations created by flaws.

The silicate glasses become mechanically weaker when heat-treated in the presence of water-vapor. However, it can be made strong if heat-treated while held under a sub-critical tensile stress at a temperature far below the glass transition temperature. This added strength is attributed to the formation of a compressive stress layer on the surface of the glass, created by a surface stress relaxation process that occurs while being held under the tensile stress.