Measurement of yarn shape and nesting in plain-weave composites

The strong dependence of composite properties on fiber orientation suggests that the yarn shape of composites reinforced with woven cloth is an important microstructural feature. This paper develops methods of quantifying yarn shape. Two measures of yarn shape and one measure of cloth nesting are proposed, viz. inclination angle, crimp angle, and angle match. The measurements can also provide best-fit sinusoidal descriptions of yarn shape. Computer-aided image processing techniques are developed to make the measurements, providing statistically reliable data in a reasonable amount of time. Examples of yarn shape measures are given for a set of carbon/carbon composites reinforced with plain-weave cloth. The data illustrate the statistical variability of yarn shape, that sinusoidal descriptions of yarn shape may not be accurate, and that yarn shape can change significantly during laminate processing.