The effects of fatigue and weathering on the failure behavior of commercial soda-lime-silicate glass

The principle objective of this research is to advance our understanding of the effects of humid conditions on the strength and susceptibility to fatigue of soda-lime silicate (SLS) glass. The two-point bend method was used to evaluate the fatigue characteristics and the degradation of failure strain of fibers drawn from melts of commercial soda-lime silicate glass and exposed to various environmental conditions. Soda lime silicate glasses from two commercial products but with similar nominal compositions were examined. One glass had pristine failure strains about 10% greater than the other, but both had similar fatigue parameters. The fatigue parameter increased from 16 to 25 when SLS glass was exposed to 80% relative humidity (RH), 50°C conditions for 28 days, indicating a decrease in susceptibility to fatigue. However, failure strains decreased by 80%. These results were attributed to changes in the glass surface due to the preferential leaching of alkali ions during weathering. The dealkalized surface was less susceptible to fatigue effects, but the damage induced to these surfaces reduced failure strain. Weathering SLS fibers in 10%RH, 50°C conditions for over 30 days, however, did not change the fatigue parameter, nor did it significantly reduce failure strain. In fact, failure strain increased by about 10% over the first three days of weathering in these conditions. Similar results were also observed for fibers weathered in 40%RH at 50°C and 25°C and were attributed to the dealkalization of the glass surface without the subsequent creation of damage sites that were created after exposure to 50°C/80% RH air --Abstract, page iii