Stress corrosion and droplets formation in calcium phosphate and calcium alumino-phosphate glasses

Subcritical crack growth and crack closure are analysed using the double cleavage drilled compression method, in two calcium phosphate-based glasses. The measurements of the crack velocity as a function of temperature, from ambient to 250 °C, are reported for two different relative humidity levels. Studied glasses present unusual trends characterized by a non-gradual shift of V–K I curves versus temperature. Moreover, when the load is released and crack closes, expulsion of a “liquid-like” phase is observed forming droplets along the crack path. These droplets are only formed at certain temperatures, but both under high and low water humidity. They evolve towards residues when temperature is decreased.