Pulsed Photothermal Radiometry for Measuring Subsurface Air Gap Thickness or Contact Thermal Resistance

摘要

The pulsed photothermal radiometry technique is applied to investigate a layered structure composed of an opaque film separated from a thick substrate by an airgap of thickness delta, or more generally, by a contact thermal resistance R. The PPTR signal shape at certain delay times from the excitation pulse is found to be very sensitive to the value of delta up to a few hundred microns in thickness. We show how the signal shape can be deconvoluted to give delta thus providing a quantitative non-destructive tool for delamination mapping. The present technique is also used to more generally quantify the value of R between a coating and a substrate; if we expect that R is related to adhesion strength (with R decreasing for better adhesion), the measurement of R also provides a new nondestructive detection method for adhesion strengths. Keywords: Layered structure; Airgap; Contact thermal resistance; Photothermal radiometry; Delamination; Coating; Thin film; Nondestructive testing; Reprints. (jhd)