21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-3.3.2

QUANTITATIVE AND QUALITATIVE ASPECTS OF THE SHEAR-SENSITIVE LIQUID CRYSTAL COATING METHOD

Reda D. C., Wilder M. E.
NASA Ames Research Center, USA

Keywords: shear-sensitive, liquid crystal coating

When a shear-sensitive liquid crystal coating is applied to a planar surface and illuminated from the normal direction by white light, then observed from an oblique above-plane view angle, its color-change response to shear depends on both shear stress vector magnitude and the direction of the applied shear vector relative to the observer's in-plane line of sight. At any surface point, the maximum color change is always seen or measured when the local shear vector is aligned with, and directed away from, the observer; the magnitude of the color change at this vector/observer aligned orientation scales directly with shear stress magnitude. Conversely, any surface point exposed to a shear vector with a component directed toward the observer exhibits a non-color-change response, always characterized by a rusty red or brown color, independent of both shear magnitude and shear direction. Surface slope inclinations of±15 deg, measured relative to the planar-surface baseline, have been shown not to alter these fundamental characteristics. Based on this knowledge, full-surface shear stress vector visualization and measurement methodologies were formulated and successfully demonstrated. The present paper reviews the observations and measurements that led to the development of these methodologies and applications are discussed.

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