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 damage microcrack is assumed to be an ellipsoid and its aspect ratio is defined by the ratio of the major axis to the minor axis. Two models of microcrack splitting are developed, namely a high-aspect ratio model and a grain-boundary 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 cylindrical pore channels will be formed. Grain boundary grooving may split a microcrack when the crack aspect ratio is larger than a threshold value. The value 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.