Remote Determination of the Two-Dimensional Diffusivity Tensor in Thin Plates

In metals and graphite-epoxy composites, the high-strength elements are also the prime thermal conductors. Flaws and failures in these elements are expected to produce anomalies in diffusivity. Most measurements of diffusivity in thin plates depend on thermal flow through the plate, and so are insensitive to these anomalies. In contrast, this technique depends on thermal flow parallel tc the plate faces, increasing the sensitivity to anomalies. patterns and thermal imagery, the diffusivity tensor is measured in a manner which is remote, noncontacting, and nonreliant on independent determinations of emissivity or thickness. The measurement is accomplished through analysis of thermal patterns evolving from heated lines with varying orientations. Also calculated is the rate of heat loss to the surroundings, a significant factor in thin plates. The work reported includes measurements in stainless steel and unidirectional graphite-epoxy composite material. Through the use of highly controlled heating