REPEATED INDENTATION EFFECT ON LEAD ALKALI AND SODALTME GLASS UNDER SUBCRITICAL LOADS PRIOR TO CRACK INITIATION

摘要

Fatigue related fracture studies on brittle materials has become predominant in recent time due to large application of such materials in different areas encountering fluctuating stresses. Among several method adopted for fatigue studies, indentation is one of them. Unlike the conventional method involved in initiating a crack with a critical load followed by repeated indentation at the same spot for crack growth and fatigue studies, this study was carried out with Vicker's indentation on lead alkali and sodalime glass to initiate cracks by repeated indentation at a singular point with subcritical loads of 0.1N, 0.15N, 0.25N, 0.50N and 1.0N. The diagonal length was measured after five consecutive cycles. The observed increase in the diagonal lengths to a limit when surface crack initiated was attributed to the increase in the plastic deformation with repeated cycling, The initiation of the surface cracks was attributed due to the accumulation of residual stress in each cycle thereby exceeding the fracture stress of glass.