U. Ramamurty, RETARDATION OF FATIGUE-CRACK GROWTH IN CERAMICS BY GLASSY LIGAMENTS -A RATIONALIZATION, Journal of the American Ceramic Society, 79(4), 1996, pp. 945-952
In high-temperature fatigue crack growth (FCG) experiments on ceramic
materials containing amorphous grain boundary phases, the crack growth
rates under cyclic loads were observed to be lower than those predict
ed solely on the basis of crack growth velocities measured under stati
c loads, In this paper, a rationalization was offered for such a behav
ior by means of a phenomenological glass-bridging model which takes th
e relaxation behavior of glass into account, In ceramics which exhibit
subcritical crack growth through cavitation ahead of the crack tip, t
he maximum stress intensity factor of the fatigue cycle required to in
itiate FCG was observed to be always greater than or equal to the thre
shold stress intensity factor for crack growth under sustained far-fie
ld loads. This trend was also explained with the aid of the glass-brid
ging model and invoking the equivalence between bridging and damage zo
nes, The elevated temperature FCG behavior of nitride-based ceramics w
hich exhibit grain bridging in the wake during crack propagation was d
iscussed and contrasted with oxide-based ceramics which show glass bri
dging.