Nondestructive evaluation techniques using infrared and terahertz waves were employed to examine an aged violin and an inlaid dish. The results suggest that active thermography can rapidly reveal the general features of deterioration, while optical coherence tomography and THz imaging visualise cross-sectional images by scanning. These techniques are complementary and provide useful information for conservation planning.

In nondestructive evaluation (NDE), pulsed phase thermography (PPT) is a commonly used technique which relies on phase contrast to detect defects. This study presents a methodology to investigate how changes in signal processing and geometrical parameters affect phase contrast. Analytically simulated thermal signals are used to evaluate the phase contrast for varying sample thicknesses and defect sizes, relative to a fixed defect depth. To address the issue of spectral leakage, phase contrasts are recorded using both rectangular and Hamming windows before transformation into the frequency domain. A Gaussian process regression (GPR) modelling scheme is used to observe the relationship between phase contrast and geometrical parameters. The results suggest that both the choice of windowing function and geometrical factors can influence defect detection, offering insights to improve the reliability of PPT-based inspections.

Classical active thermographic testing of industrial goods has mostly been limited to generating 2D defect maps. While for surface or near-surface defect detection, this is a desired result, for deeply buried defects, a 3D reconstruction of the defect geometry is coveted. This general trend can also be well observed in widely used NDT methods (radio- graphy, ultrasonic testing), where the progression from 2D to 3D reconstruction methods has already made profound progress (CT, UT phased array transducers). Achieving a fully 3D defect reconstruction in active thermographic testing suffers heavily from the diffusive nature of thermal processes. One possible solution to deal with thermal diffusion is the application of the virtual wave concept, which, by solving an inverse problem, allows to extract the diffusiveness from the thermographic data in the post-processing stage. What is left follows propagating wave physics, enabling the usage of well-known algorithms from ultrasonic testing. In this work, we present our progress in the 3D reconstruction of deeply
buried defects using spatially structured laser heating in conjunction with applying the well-known total focusing method (TFM) in the virtual wave domain.

To replicate delaminations at the coupon and substructural scales, simulated defects are often introduced into test specimens; therefore, understanding their behaviour within the laminate is essential. Full-field imaging is employed to investigate the effects of artificial defects in Carbon Fibre Reinforced Polymer (CFRP) composites. Centre Crack Ply (CCP) specimens are used to evaluate the Mode II fracture toughness of laminated composites from a simple tensile test. Two batches of specimens are manufactured using IM7/8552. Artificial defects are introduced using a steel film insert of 5 µm thickness. For the first type of samples, the inserts were coated with Frekote release agent, while for the second type, the steel inserts were incorporated into the laminate without coating. Additionally, a third batch of specimens with a [0₄, 90]s lay-up is manufactured. Thermoelastic Stress Analysis (TSA) and Digital Image Correlation (DIC) are employed to obtain full-field temperature and displacement data from the tested samples. The inclusion of 90-degree plies enhances thermal contrast exploiting their anisotropic mechanical and thermal properties. First, the specimens are tested under monotonic loading to failure, with DIC used to capture strain distributions at damage initiation and failure. In addition, acoustic Emission is employed to evaluate damage initiation. Load drops provide an indirect evaluation of fracture toughness. Results show that full-field imaging is capable of establishing how the release agent and the lay-up configuration influence damage initiation and propagation. The non-adiabatic thermoelastic response is shown to be effective in observing subsurface damage. Finally, a novel approach to evaluate fracture toughness from the temperature increase at the failure event is proposed.

Sonic-IR method is an innovative approach to defect detection. Ultrasonic waves are input to the inspection object, and the frictional heat generated by friction with the defect interfaces is detected by an infrared camera. A notable advantage of this method is its superior detection ability to detect closure defects that are often missed by other inspection methods. However, the conventional Sonic-IR method pressing an ultrasonic transducer directly against the inspection object may cause deformation or surface damage, depending on the material and shape of the object.

As a method to solve this problem, the immersion Sonic-IR testing, in which ultrasonic waves are input to the inspection object through a water, has been proposed. However, this method has a problem in defect detectability because of the small frictional heat at the defects. Large-diameter bubbles in water are difficult to collapse, and also cause scattering and attenuation of ultrasonic waves. In contrast, small-diameter bubbles are easily collapsed so that cavitation, which is a source of vibrational energy, is likely to occur.

The objective of this study is to investigate the influences of dissolved oxygen and microbubbles on the sound pressure level in the water and heat generation at defects in order to improve the defect detectability of the immersion Sonic-IR testing.

Moisture in building materials, particularly in cultural heritage structures, can cause reduction of mechanical strength, decrease of indoor comfort and alteration of thermal properties, aesthetic decay, and even material loss. To non-invasively quantify moisture content in porous materials, Active Infrared Thermography was used. The method was applied in the laboratory on brick sample with different moisture contents, as well as on a reference stone sample with known thermophysical properties, to evaluate the thermal inertia as a function of water content using a comparative approach. A heat flux was applied to the sample using a lamp, and thermal inertia was derived from the absorbed heat, influenced by the material's absorption coefficient. An indirect optical calibration enables estimation of this coefficient without applying high-emissivity or high-absorption coatings, preserving the integrity of sensitive heritage materials.

Cold Spray Additive Manufacturing (CSAM) is a solid-state process increasingly used for structural repairs in aerospace and energy sectors. It enables the deposition of dense material at low temperatures by accelerating metal particles to supersonic velocities, thereby reducing thermal distortion. However, the structural integrity of CSAM repairs—particularly at the interface between the deposited layer and the substrate—remains a critical concern. Various post-treatments and characterisation methods have been explored to optimise performance. While X-Ray Computed Tomography (XCT) is effective for sub-surface inspection, it cannot be applied in-situ during mechanical testing. Digital Image Correlation (DIC), a surface-based method, also lacks sub-surface sensitivity. To address this, Infrared Thermography (IRT) was employed alongside DIC during tensile and fatigue testing of aluminium CSAM-repaired specimens. A cooled IRT camera operating at 200 FPS captured thermal data, with Lock-in processing subsequently applied in post-processing. IRT successfully detected early interfacial damage and enabled tracking of crack propagation, which was later confirmed through fracture surface analysis. This extended abstract presents findings from fatigue tests using IRT. Results from DIC and tensile tests will be discussed during the conference presentation.

We examined the effect of SiO₂ passivation on the parameters of mesa heterostructure InAs/InAsSbP photodiodes with a spectral responsivity 50% cut off at 3.5 µm at 295 K, specific to the InAs absorber layer. The R₀A product was found to increase by 30% after passivation of the devices of 113 µm in diameter, up to 0.9 Ωcm², while for those with a diameter of 1.13 mm, R₀A of 2.2 Ωcm² was achieved, with a value of D* > 3×10⁹ cmHz^1/2/W at the peak of the spectrum, 1 kHz, 0 V bias, 295 K. To the best of our knowledge, this is the highest R₀A value at room temperature reported to date for a photodiode with an InAs absorber.

Non-destructive testing and evaluation methods not only demand various experimental techniques but also adopts efficient post-processing approaches on the obtained experimental data to enhance the defect detection capabilities. Among these, widely used experimental techniques such as pulse compression favourable thermal wave imaging approaches and associated post-processing approaches gained significance due to their capabilities including remote, safe, wide-area inspection along with improved defect detection sensitivity and resolvability. In this work, experiments have been carried out on a glass fibre reinforced polymer material having flat bottom holes as to demonstrate the effectiveness of different pulse compression favourable thermal wave imaging approaches and their defect detection capabilities by considering the signal to noise ratio as a figure of merit. The results clearly indicate that the correlation (matched filter) based post-processing approach offers significantly superior defect detection capabilities compared to the widely used frequency-domain phase analysis-based data processing approach.

This paper presents an experimental study using test specimens to demon-strate that the filling status of concrete on the inner surface ofathick wall’s steel platescan be monitored on the outside using infrared cameras. In previous research, it wasfeasible to monitor the filling statusof concrete onthewallwith a steel plate thickness of10mmor lesson the outside using infrared camera.In this study, the steelplate thick-ness is increased from10mm to 22 mm and 32 mm.