Measurement of Void Content and Distribution in Composite Materials through Digital Microscopy

The use of digital optical microscopy techniques to measure the volume fraction and spatial distribution of voids in composite materials manufactured by filament winding is presented and discussed. The volume fraction was measured using the usual technique of object measurement from several individual fields and using mosaic images formed by assembling low magnification fields. The results obtained were consistent showing the usefulness of the mosaic image approach that also provides a global view of the complex microstructure of the material. From the mosaic images contour maps of void number and void area fraction were generated providing a semi-quantitative evaluation of void distribution. Using the tessellation technique for neighborhood analysis the coefficient of variation of the distance between nearest neighboring voids was measured. This parameter allows a quantitative measure of void spatial distribution, revealing homogeneity or clustering of the void population.