Influence of crack geometry and loading mode on fracture and fatigue of soda-lime-silica glass

Fracture toughness and cyclic fatigue resistance of soda-lime-silica glass in water environments are studied in this work. Novel sandwiched beam (SB) specimens are used to measure the fracture toughness in mode I, mode II and mixed mode loading. Both SB samples and Vickers indented bars are used for the analysis of cyclic fatigue resistance in mode I and II. Values of K IC=0·74 MPam1/2 and KIIC=0·64 MPam1/2 were obtained. Results for mixed mode fracture show that failure in soda-lime-silica glass can be described by the maximum normal stress criterion. Therefore, defect propagation is controlled by the near crack tip stress field. Cyclic fatigue tests furnish similar results for the crack geometry in mode I loading. Comparison of experimental results with predictions based on the typical power law for sub-critical crack growth in glass shows that cyclic fatigue resistance is also related to the typical stress corrosion mechanism for glasses in contact with a humid environment resulting in lifetime becoming longer under alternating loads (R=-1) than under pulsed stress (R=0). Cyclic fatigue resistance is also larger under mode II than under mode I. Fractographic analysis of samples subjected to cyclic loads shows that crack propagation driven by an oscillating load is characterised by rib marks attributed to arrest of the crack front when the load decreases below zero or below the fatigue limit in each cycle.