Failure strains of commercial silica, soda-lime-silicate, and E-glass fibres were measured using two-point bending in room temperature humid air. Humidity dependence and dynamic fatigue behaviour were studied, and the fatigue reaction orders in terms of humidity were determined. In the humidity range tested (~0.1% to ~100%), the dynamic fatigue parameters for silica and E-glass are found to be greater in lower humidity, whereas the fatigue parameters for soda-lime-silicate is independent of humidity. The humidity dependence of failure strains for all three glasses was more pronounced in high humidity (~10 to ~100%) than in low humidity (~0.1 to ~10%), indicating that the reaction order decreases with decreasing humidity. These observations were correlated with the different structures of the glasses and their corresponding fatigue mechanisms.
