Estimation of three-dimensional connectivity of internal defects in coatings using fractal analysis

The connectivity of a porous medium is an important topological characteristic, which indicates the extent to which internal defects (e,g,, porosity or micro/macrocracking) are connected, Up to now, connectivity has been studied by various stereological procedures based on the "net volume tangent counts" proposed by DeHoff and performed on pairs of consecutive sections of an interconnected structure. However, the drawbacks of these procedures are their use of invasive techniques and manual counting. Connectivity is here studied with fractal geometry instead of conventional Euclidean geometry, The porosity network of a thermal spray sample may be fractal, and so can be at least partly characterized by fractal dimension. Modifications in connectivity could be reflected in changes in the fractal dimension. if changes in the connectivity, as characterized by changes in fractal dimension, can be adequately demonstrated by the computerized analysis of confocal scanning laser microscope (CSLM) images, then the technique may provide a useful, noninvasive way of improving the characterization of thermal spray coatings. The study also seeks to show how connectivity differences affect the mechanical properties of the coating and whether fractal analysis is able to detect these changes in mechanical properties.