A numerical simulation of the R-curve behavior in microcracking materials

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Abstract
We propose several models for crack propagation in ceramic materials with microcrack formation and coalescence. The models differ in the relative time scales involved in the internal relaxation processes and the external loading rate. We find that when the external loading rate is very high, a rising R-curve is obtained. For slow external loading, the results depend upon the relative rate of the different internal relaxation processes and upon the distribution of the critical stresses needed to form the microcracks. In this regime, the existence of a rising R-curve behavior is found to be primarily due to microcrack shielding.