Comparison between Microwave Infrared Thermography and CO<sub>2</sub> Laser Infrared Thermography in Defect Detection in Applications with CFRP

Abstract

This paper presents two infrared thermography methods with CO 2 Laser excitation and microwave excitation applied to defect detection in CFRP. The tests were conducted with two specimens, one with defect, and another one without defect. On two concrete plates 40 cm × 40 cm × 4.5 cm were reinforced by CFRP; the defects were made by the absence of adhesive on an area 10 cm × 10 cm. The specimens were heated by microwave, generated by a commercial magnetron of 2.45 GHz and guided by a pyramidal horn antenna, with a power of 360 W within 150 s. Another series of the tests was conducted with CO 2 Laser, wavelength 10.6 µm, by heating the samples with a power of 300 W within 40 s. An infrared camera sensitive to medium waves in range of 3-5 μm, with a detector of 320 × 256 matrix detector in InSb (Indium Antimonide), was used to record the thermograms. As a result, the CO 2 Laser excitation is better for the delamination detection in CFRP. This study opens interesting perspectives for inspecting other types of defects in materials sciences; the microwave excitation is suitable for the deep defects in the materials whereas the CO 2 Laser excitation is better for the defects near the surface of the materials.

An investigation and review into microwave thermography for NDT and SHM

“…Clearly, defect can be found in the middle of the sample. The absence of adhesive made it hotter than other area without defect [17]. …”

“…The antenna was placed in the 45° direction. Thermograms were recorded at 1 Hz by a computer, synchronized to the infrared camera, using the ALTAIR program [17]. The specimen was heated with a power of 360 W for 150 s. The tests on both samples (with defect, and without defect) had the same procedure.…”

“…Some scientists used the microwave thermography to detect mine and mine surrogate signatures [15,16]. Recently, microwave thermography has also been investigated in NDT and structural health monitoring (SHM) fields [17][18][19][20][21][22][23][24].…”

Detection of reinforcement bars in concrete slab by infrared thermography and microwaves excitation

“…Moreover, thermal stimulations applied from the external surface limit the auscultation depth or impose long-term tests. This paper aims to present the development of a new active infrared thermography method based on a microwave excitation system [3]. Compared to other sources traditionally used in active infrared thermography, the microwaves can propagate into the volume of a concrete element.…”

Principles and Applications of Microwave Testing for Woven and Non-Woven Carbon Fibre-Reinforced Polymer Composites: a Topical Review

“…Keo et al [53] used a commercial 2.45 GHz magnetron and an IR camera to detect a defect (absence of adhesive) in a CFRP plate. A 360 W microwave signal was applied to heat the sample for 150 s. It was found that the defect area was hotter than the non-defect area.…”