Abstract
An estimation is carried out to determine a length of downward extension of a crack and an upper limit of depth of cut preventing its extension in orthogonal cutting of ceramics. Fracture mechanics is applied to solve a crack extension problem in the elasto-plastic tensile stress field which initiates and grows to some extent in a work by the tool progress. Two different values in fracture toughness of a work are used depending upon levels of pre-existed crack sizes which are appropriate for determining the length of the crack extension and the upper limit of depth of cut respectively. Estimated values of the length of the crack extension and the upper limit of depth of cut in various ceramics are very different from each other : the lengths of the crack extension in glass ceramics (Macor) and ZrO2 are considerably smaller than those in soda-lime glass, SiC and Al2O3, and the upper limit of depth of cut in Macor is extremely large (e.g. 14 μm in Macor and 1μm in SiC). The estimation concerning both the length of the crack extension in various depths of cut and the upper limit of depth of cut in Macor is confirmed to be valid by experiments.
