Crack-location-dependent R-curve behavior in Si 3N 4

Abstract

The rising crack resistance ( R-curve) behavior in a hot-pressed Si 3N 4 with an elongated grain structure was studied by observing the stable growth of annealed indentation-induced cracks during the bending test. The experimental data corresponding to each individual crack were analyzed according to an exponential function proposed by Ramachandran and Shetty. [Ramachandran, N. and Shetty D. K., Rising crack growth-resistance ( R-curve) behaviour of toughened alumina and silicon nitride. J. Am. Ceram. Soc., 1991, 74, 2634–2641]. It was found that the measured R-curve is strongly dependent on the crack location. Due mainly to the existence of a microstructural driving force for crack growth, all cracks may start to propagate at nearly the same level of the applied stress intensity. During the subsequent stable growth, however, the variations of crack resistance with crack extension may be different for different cracks located in different sites of the surface of material. The effect of the random orientation of the elongated grains within the material on the interaction between the bridging grain and the propagating crack was suggested to be the main cause of the crack-location-dependence of the measured R-curve behavior.