https://doi.org/10.1351/goldbook.12769
Quantity characterising the fragility or the strength of a glass at a given temperature \[m = \left (\frac{\rm{d} \log_{10} \tau}{{\rm{d}} (T_{\rm{g}}/T)} \right)_{T = T_{\rm{g}}}\] \(\tau\) = relaxation time [\(\pu{s}\)]; \(T_{\rm{g}}\) = glass-transition temperature [\(\pu{K}\)]; \(T\) = temperature [\(\pu{K}\)].
Notes:
- The value of the fragility index depends on the thermal history of the glass.
- The values of \(m\) range from \(m \approx 16\) for a very strong glass to \(m \approx 250\) for a very fragile glass.