Abstract
Growth rate of surface microcracks given by machining has a great influence on the life of ceramics with extremely low toughness.
In this paper, the steady state growth rate of cracks in ceramics (Al2O3, Si3N4, SiC) under repeated bending and tensile loads in vacuum were examined using scanning electron microscopy.
Major results obtained are as follows.
1) Growth rate of cracks in the second region showed good correspondence to stress intensity factor range in all ceramics tested.
2) Power law for crack growth was recognized in ceramics, too. Exponent m for the ceramics was nearly equal to that for metals under a repeated tensile condition and was one order of magnitude lower than that for metals under a repeated bending condition.
3) Exponent m was larger in case of a repeated tensile load and coefficient C was larger in case of a repeated bending load for the Al2O3 ceramic.
4) Growth rate of cracks in the second region was influenced greatly by glass phase at the grain boundaries.
