Finite element analysis of the splitting and cylinderization processes of damage microcracks

A two-dimensional finite element method is applied to analyse the splitting and cylinderization processes of a damage microcrack during healing. These processes are controlled by surface diffusion. The cross section of the da mage microcrack is assumed to be an ellipsoid and its aspect ratio is defin ed by the ratio of the major axis to the minor axis. Two models of microcra ck splitting are developed, namely a high-aspect ratio model and a grain-bo undary grooving model. The splitting processes based on the two models are simulated. A critical aspect ratio is predicted, below which the microcrack will directly evolve into a cylindrical pore channel if there is no other energetic mechanism to split the crack and above which two or more cylindri cal pore channels will be formed. Grain boundary grooving may split a micro crack when the crack aspect ratio is larger than a threshold value. The val ue of the threshold is predicted for a grain boundary perpendicular to the centre of crack surface. An approximate formula is given for predicting the critical grain boundary energy, at which the microcrack can be split, as a function of microcrack aspect ratio.