DEFORMATION OF SODALIME GLASS UNDER REPEATED INDENTATION

Fracture mechanics studies on glass by indentation techniques have bec ome predominant in recent times. Several techniques have been adopted to initiate crack in the material followed by repeated indentation at the same spot for crack growth and fatigue studies. However glass subj ected to to repeated indentation at a point prior to crack initiation at a subcritical loads phenomenological to metal fatigue was not syste matically investigated. Experiment was conducted to initiate cracks on normal sodalime glass by repeated indentation at a single point with different subcritical (0.1 N, 0.15 N, 0.25 N, 0.50 N, 1.0 N) loads. Ex periment was discontinued the moment crack was observed to occur. The length of diagonals were found to increase with each indentation leadi ng to crack initiation. This observation was analysed considering the plastic component and the residual force developed during each indenta tion cycle and a model has been developed to correlate the contributio n of cumulative residual stress for crack initiation.