MOISTURE ASSISTED SLOW CRACK EXTENSION IN GLASS PLATES.
NAVAL RESEARCH LAB WASHINGTON D C
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Exploratory studies of moisture assisted stable slow crack extension in a 4mm thickness plate glass were made. It was found that satisfactory control of crack orientation could be obtained using a double cantilever type specimen if the total angle bisected by the crack was as large as 90 degrees. No side grooves or guiding scratches were required or used. Trials were made at room temperature using 50 percent relative humidity, dessicated air, and saturated air. The moist test results were difficult to interpret. The remaining results suggest that, for a fixed stress level near the crack, the water assisted crack speed is nearly proportional to the water content of the air. The restricted mobility of water molecules between glass surfaces less than 50 A apart is the dominating influence controlling shape of the response curves crack speed as a function of stress field force. The crack speed magnitude and the leveling of crack speed prior to onset of fast fracture are closely related to compositional and structural aspects of the glass. Author
- Ceramics, Refractories and Glass