| In general, the compressive strength of brittle materials such as glass, ceramic, rock, etc. is much higher than their tensile strength. If brittle materials fail according to a maximum tensile stress criterion, it is a fair question to ask how these materials can fail when subjected to uniaxial compressive stress and why the compressive strength is so high. This question was answered by A. A. Griffith many years ago (1924) by postulating the presence of narrow hair line cracks. While the Griffith theory of crack initiation is in good qualitative agreement with experiment, it is in poor quantitative agreement. This dissertation introduces a new approach to the brittle fracture of materials based on defects in the form of small circular voids and stress concentrations associated with them.; The indentation fracture of brittle materials is also discussed and applications to the cutting of brittle materials considered. The advantages of the sharp glass cutting wheel are identified and discussed in terms of the behavior of brittle materials. A sharp wheel indenter which involves a low friction force and produces deep median cracks beneath the indenter is applied to silicon wafer scribing to eliminate undesired surface damage such as chevron and lateral vent cracks. From the standpoint of crack control in brittle material scribing, a promising new method referred to as the 'negative friction method' is introduced which leads to the scribing of glass and silicon wafers with far less damage of defect formation during scribing. |
