<title>Ultrasound lock-in thermography: feasibilities and limitations</title>

TLDR

Conventional thermal wave imaging using optical excitation is sensitive to all thermal boundaries, whereas ultrasound energy deposition selectively heats regions with enhanced mechanical loss angle. The study investigates the applicability of ultrasound lock‑in thermography for maintenance and inspection. ULT detects defects by monitoring thermal waves emitted from areas of enhanced loss angle that absorb ultrasound. The authors demonstrate defect detection in thick composites, vertical cracks, and hidden corrosion, while also discussing limitations imposed by ultrasound use.

Abstract

Conventional thermal wave imaging methods based on optical excitation are sensitive to all thermal boundaries and structures. However, if ultrasound is used for energy deposition, areas of enhanced mechanical loss angle are heated up selectively. As defects are usually correlated with an enhanced loss angle, ultrasound lockin thermography (ULT) is a defect-selective NDE method. Thermal wave emission from defects is monitored that are activated by absorption of ultrasound. In this paper we investigate the applicability of ULT for maintenance and inspection. Examples are presented showing the detection of defects in thick composite materials, of vertical cracks in several materials, and of hidden corrosion. Limitations given by the use of ultrasound are also discussed.