QUANTIFICATION OF MICROCRACKING IN BRITTLE-MATRIX COMPOSITES

The mechanical properties of brittle-matrix composites are often closely coupled to the generation and propagation of many small cracks. However, the role of microcracking is complex and not well understood on a quantitative basis. Better understanding will require an ability to quantify the crack morphology and how that structure evolves. This paper describes techniques to classify, count and measure the length, spacing and orientation of microcracks. Digital image processing is applied to make the measurements, thereby providing time-effective, reproducible, statistically significant estimates of crack morphology. A key feature of the image processing strategy is to abstract the crack structure to a set of medial axis lines. Proper interpretation of the data requires an understanding of the measurement limitations which are related to size resolution, choice of processing parameters, specimen preparation, and use of sectional views. The techniques are illustrated by data drawn from a carbon-carbon composite laminate. The methods are adaptable to a wide range of materials, and can provide a rich, readily accessible, quantitative description of microcrack structure.